UNIT5 RUN FOR YOUR LIFE CELLULAR RESPIRATION
metabolism This refer to all the reactions that take place p lace in a cell/ types of metabolism reactions and examples i) Catabolism:- This is the breakdown of complex molecules to simple ones.g respiration, deamination(removal of the amino-group from the amino-acid). ii) Anabolism:- These are reactions which form complex molecules from simple molecules e.g photosynthesis synthesis, lipid synthesis
metabolic pathways and examples -
These are sequence of enzyme en zyme controlled reactions with the formation of intermediate compounds e.g glycolysis, Krebs cycle,etc
structure of the ATP molecule
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It consists of an organic base that is Adenine which is joined to a pentose sugar(ribose)
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Which inturn is linked to 3 organic phosphor-anhydride bonds.
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Which can be broken by hydrolysis to give out free energy. Phosphoanhydride bonds
P Adenine
P
P
Ribose
importance of ATP -
It provides energy to perform mechanical work (by movement of muscles/spindle fibres), cell movement(e.g. cilia,WBC, sperms).
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It is also required during active transport e.g. uptake of salt by roots, uptake of digested food from the villi, uptake of mineral salts and glucose in the PCT
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It is required during synthesis of macro-molecules e.g. proteins.
ATP formation
It is formed when ADP combines with an inorganic phosphate and energy is derived from respiration to form ATP. C6H12O6+6O2
6CO2+6H2O+Energy
ADP + P+ Energy
AT P
Cellular respiration
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This is the oxidation of food molecules e.g. e. g. glucose in order to obtain free energy.
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It consists of chemical reactions which can be grouped into three stages:i.
Glycolysis
ii. Kreb Kreb’’s Cycl Cyclee iii. Electron Electron transport transport system/oxidat system/oxidative ive phosphorylation phosphorylation glyclosis -
This is the breakdown of glucose through a series of reactions to form pyruvate (pyruvic acid)
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It takes place in the cytoplasm of the cell.
Describe glycolysis
The glucose molecule is phosphorylated using ATP (Pump Priming) and this forms glucose-6 phosphate which;
i.
Acti Activa vate tess the the gluc glucos osee mol molec ecul ulee
ii. ii.
It make makess the the molec molecule ule larg largee and hence hence cannot cannot move move out of the the cell cell..
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The glucose -6- phosphate is then converted to fructose -6- phosphate.
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The fructose -6- phosphate is then phosphorylated phospho rylated to form fructose -1,6- diphosphate.
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This is then broken down into two molecules of glyceraldehydes -3- phosphate.
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This glyceraldehydes -3- phosphate is then conv erted to pyruvate (2 molecules of 3 carbon atoms each)
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In addition 2 hydrogen atoms 2H are released and at the same time the reactions are exothermic and energy is released which is enough to convert 2 ADP molecules into 2ATP molecules by each glyceraldehydes glyceraldehydes -3- phosphate
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Hence the net production of ATP during glycolysis is 2(4-2)
Flow chart of glycolysis
Glucose
Glucose -6- phosphate
Fructose -6- phosphate
Fructose -1-,-6- diphosphate
(2m) glyceraldhide -3- phosphate(3c)
(2m) pyruvate(3c)
2ATP formed x2=4 3ATP formed x 2=6
Net ATP formed = 6+4-2= 8ATP
Controlling
glycolysis
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When energy demands are high h igh then the rate of glycolysis also increases and vice versa
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Enzymes controlling the reaction e.g. phosphofructokinase p hosphofructokinase for pump priming are inhibited by high levels of ATP and citrate.
Structure of mitochondria
Kreb’s cycle -
Q
This is the process by which the pyruvate is broken down in the presence of oxygen to give co2 and hydrogen atoms. It takes place in the matrix of the mitochondria.
Describe the Kreb’s cycle?
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The pyruvate is converted into a two carbon called acetyl co. enzyme A and in the process CO2 is released with the help of decarboxylase enzyme. - At the same time two hydrogen atoms are released with the help of dehydrogenase enzyme. - A (4C) acid (oxalo acetate) combines with acetyl co. enzyme A to form a (6C) acid called citrate. - The (6C) acid (citrate)is then converted to a (5C) acid with removal of CO 2 and,2 hydrogen atoms - The 5c acid is converted to 4c acid (succinate) with removal of co2 ,2hydrogen atoms and 1ATP molecule is formed. - The (4c) acid succinate is converted to another (4c) acid called malate with the removal of 2 hydrogen atoms. - The malate is then converted to oxalo acetate with the removal of two hydrogen atoms. The flow chart. Link reaction (2m) pyruvate
Electron transport system (ETS)
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This is the means by which energy inform of hydrogen atoms from the Kreb’s cycle as well as the glycolysis are converted to ATP. The hydrogen atoms are attached to carriers which are progressively at lower energy levels.
Main carriers involved in the electron transport system i) Co enzymes i.e. NAD and FAD both of which act as hydrogen acceptors for the hydrogen released from the Kreb’s cycle. NAD: - Nicotine amide - Adenine - Dinucleotide
ii) iii) iv)
FAD: - Flavine - Adenine - Dinucleotide Cytochromes:- they are protein pigments with iron group like haemoglobin and they receive electrons from NAD/FAD. Cytochrome oxidase :-it is an enzyme that receives the electrons from the cytochromes. Oxygen: - this is the final hydrogen acceptor in the chain and it is reduced by hydrogen and water is formed.
ATP molecules formed during electron transport system NB: 3 ATP molecules are formed when two hydrogen atoms pass through the carriers
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It takes place in the cristae / inner membrane of the mitochondria. - As the hydrogen atoms are passed on from one carrier to another, the energy released is used to make ATP. - Initially hydrogen atoms are passed along the chain up to FAD after which they split into electrons and protons. - Only the electrons pass through the carriers i.e. the cytochrome - At the end of the chain protons and electrons recombine to form hydrogen atoms which combine with oxygen to form water. - The enzymes cytochrome oxidase catalyses the transfer of hydrogen to oxygen and it can be inhibited by cyanide. - Formation of ATP through oxidation by hydrogen atoms is called oxidative phosphorylation. Oxidative phosphorylation - It is the process by which ATP molecules are formed when electrons are transferred along the carriers to oxygen whereby they become oxidized and at the same time a phosphate is added to ADP (phosphorylation) - ATP molecules are formed when one molecule of glucose is fully oxidized - During glycolysis a net of8ATP’s are formed - From pyruvate i.e link reaction and kreb’s cycle a total of 30ATP’s is formed. Therefore net production of ATP IS 30 + 8 38 ATPs NB – The hydrogen atoms from glycolysis are taken up by NAD which then moves to the mitochondria - 1 ATP molecule is required to actively transport the reduced NAD into the mitochondria. Hence 2ATP molecules are used to actively transport NAD into the mitochondria. Therefore net production of ATP = 38-2 36 ATP
chemiosmotic theory - The protons enter the intermembrane space actively (energy is used) while the electrons pass along cytochromes within the inner-membrane - The protons flow back to the matrix through the stalked particles due to their concentration gradient (the membrane is not permeable to the protons and hence they pass through the stalked particles) - This flow combines ADP and phosphate forming ATP in the presence of the enzyme ATP synthase. pyruvate in the absence of oxygen in animals as well as plants - In animals the pyruvate combines with hydrogen from reduced NAD and is converted to lactate (lactic acid)
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when oxygen becomes available it can be broken down to provide energy. In plants carbondioxide is removed from pyruvate farming ethanol which then combines with hydrogen atoms from reduced NAD and is converted to ethanol.
NB: In anaerobic respiration one glucose molecule will give rise to 2ATPs but when it undergoes aerobic respiration 36ATPs are formed. To investigate the rate of respiration - Take a manometer and introduce a coloured liquid. - This is connected to a test-tube that contains i) Living organisms at the bottom e.g germinating seeds. ii) A wire gauze which is a short distance above the living organisms holding sodalime iii) A tap which is supposed to adjust the levels of the liquid in the manometer at the beginning. - The test-tube is then immersed in a water bath (to maintain a constant temperature as respiration is affected by temperature) - Living organisms undergo respiration and the carbon dioxide given out is absorbed by soda lime (NAOH). - The volume of Co2 given out will be indicated by the rise of the liquid in the manometer - The volume of Co2 is given by
MUSCLES AND MOVEMENT Types of muscles i) Striated / skeletal / voluntary muscles - They are attached to the skeleton and they bring about movement
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They are under the control of will When observed under the microscope thy appear to be striated e.g biceps, triceps
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Smooth / unstriated / involuntary muscles: They are not striated They are not attached to the skeleton They are found in the gut and they help in peristalsis They are also found in the blood vessels e.g arteries and veins They contract and fatigue slowly
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Cardiac muscles They are found in the heart They are striated and the muscle fibres are joined by cross-connections They contract spontaneously and they do not fatigue.
ii)
iii)
l The fine structure of a striated muscles
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The muscle block is made up of the muscle fibres Each muscle fibre is made up of many myofibrils Each myofibril consists of light and dark bonds alternating The dark band (A-band) has a comparatively light region in the middle referred to as H-zone Running across the middle of the A-band is a dark line that is m-membrane Transversing the middle of the light band (I-band) is an even darker line known as the z-line. The region of a myofibril from one z-line to the next is known as sarcomere (this is the single contractile unit of the muscle) The myofibril is composed of two types of filaments i.e thick and thin. The thick filaments consist of proteins called myosin while the thin have got actin proteins. The thick filaments are confirmed to the dark bond while the thin filaments in between the thick filament into dark band. The segments on either side of A-band are particularly dark as they contain both thick and thin filaments. The H-zone consists of the thick filaments only an d that is why they are lighter than the two ends of the dark band. The cross section of the different parts is as shown below
A
B
Actin only
Myosin
C
Actin & myosin
Reaction of muscle fibres to stimuli. i) All or nothing response. - This means that if the stimulus is below a certain level, nothing happens, but if it is above the threshold level, the muscle fibre twitches (contracts) ii) Summation - This is when two stimuli are close enough together and the contractions (twitches) are so close that there is no relaxing and lengthening between them.
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iv)
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This gives the appearance of a single large contraction (twitch) and it is called summation.pg 142
Tetanus When a series of rapid stimuli is given, the muscle fibre becomes fully contracted and as short possible and it remains in the state and this is known as tetanus
NB. The muscle fibre cant remain in this condition as it eventually fatigue because the supplies of ATP and calcium are depleted. Types of skeletal muscles and the differences i) Slow twitch muscle fibres - They contract slowly and stay in tetanus for a long time.
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They are normally used to maintain body posture They have a rich blood supply. They have a lot of mitochondria and plenty of myoglobin (it has a high affinity for oxygen compared to haemoglobin and it also stores oxygen. This avoids anaerobic respiration. These muscles are known as oxidative or red muscle fibres (due to blood supply and high of myglobin and hence are deep red in colour) Glucose is the main source of energy.
ii)
Fast twitch muscle fibres - They contract very rapidly and hence they are for sudden, rapid burst of activity - They function anaerobically - They fatigue quickly - They have very few blood vessels, low levels of myoglobin, small number of mitochondria and hence they are paler in colour. - They contain glycogen stores as well as creative phosphate which can be used to form ATP from ADP - They are also known as white muscle fibres or glycolytics - There are known as white muscle fibres or glycolytics - There are more myofibrils packed as they The contractions of the skeletal muscles in terms of sliding filament theory
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Contraction occurs due to the thick and thin filaments sliding between each other.
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The thin filaments in each light bond are held together by transverse membrane referred to as z-membrane.
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The thick filaments are held by a membrane i.e M- membrane and thus are expected to slide as a unit.
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When the muscle is fully relaxed(stretched),the light band a nd H-zone become long.
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the dark ends of the dark band are relatively short.
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When contracted the light band and the H-zone become shorter and the dark ends become longer.pg 321 fa
Stretched/contracted
NB: when actin and myosin are extracted and mixed together nothing happens but if ATP is added they form actomyosin and contracts. hence the process must be an active one.
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This process involves formation of’bridges’ between actin and myosin which are then broken down during contraction.
The structure of actin and myosin filaments in association with other protein molecules. i Myosin filaments:
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It consists of two linear twisted polypeptide chains each with a globular head which has ADP and inorganic phosphates molecules bound on to it.
ii.) Actin filament:-
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It consists of 3 different types of molecules 1. Actin polymers which are made up of the monomers 2. Tropomyosin:when in relaxed state it covers the myosin bonding sites. 3. Troponin: it is attached to the tropomyosin and it is made up of three sub-units a) That which binds to actin b) That which binds with the tropomyosin c) The one which binds with calcium ions(Ca2+)
The role of actin, myosin, troponin, calcium ions,ATP and ATPase during skeletal muscle contraction?
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the myosin head (globular)have ADP and an inorganic phosphate bound to it.
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Calcium ions binds to the troponin molecules and their shape changes and they pull on tropomyosin molecules they are attached to
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The tropomyosin therefore moves away from myosin binding sites which become exposed.
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The myosin heads bind to the actin forming an actomyosin bridge.
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The ADP and inorganic phosphate are released from the myosin head
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The myosin changes shape with its head bending forward moving the action filament about 10nm along the myosin filament and therefore shortening the sarcomere.
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Free ATP binds/attaches to the head causing another shape change in myosin so that the binding of the head to the actin filament is broken.
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This activates ATpase in the myosin head which also requires calcium ions to work.
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The ATP is hydrolysed providing energy to return the myosin head to its original position i.e attached with ADP and Pi,ready to repeat the process.
Tissues of the skeletal system:1. Bone
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It is a strong,hard tissue which is the basis of the skeleton and it is made up of bone cells which are embedded in a matrix of collagen and calcium salts.
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2 Cartilage
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This is a hard but elastic tissue found between the bonds in the joints and covering the articulating (movement where the bones meet) surfaces of the bones.
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It is made up of cells called chondrocytes.
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It withstands compression forces and it is a good shock absorber.
Types of cartilage
i.
Hyaline:-
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They are found at the end of the bones
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They are also found in the nose,air passage ways and parts of the ear.
ii. White fibrous cartilage:-
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They have great tensile strengths but less flexible
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It forms the intervertebral discs and it is found between bones in the joints.
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Tendon -
It is a tissue which joins a muscle to a bone and it is made up of almost entirely white fibrous tissues.
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It is relatively inelastic (cant stretch)
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It provide alittle shock absorption if the joint is subjected to a sudden stretch.NB// if tendons stretch a lot,then much of the work done by the muscles will be wasted as they would stretch the tendons without moving the bones.
Ligaments
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They hold bones together in the correct alignment both around the joint as capsules and within the joint itself.
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They are elastic to allow the bones of the joint to move when necessary.
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They are made up of yellow elastic tissues which provides strength and elasticity.
Joint and examples
A joint is where two or more joints meet and articulate.e.g i. -
This joint is found at the hips and shoulders,and they show movement in all planes e.g shoulder ,hips ii.
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Ball and socket joint:-
Hinge joint:-
They show movement in only one plane and hence the movement is restricted.g elbow,joint,knee joint. NB//:-A membrane surrounding the cartilage produces synovial fluid which ensures friction free movement. Pg 332 fa
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How movement is brought about in organisms pg 333 fa
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It is brought about by the action of muscles on bones.
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Each of the skeletal muscles is attached by tendons to two different bones spanning at least one joint.
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When a muscle contracts it exerts a pull on the bone.
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When they relax they do not exert a corresponding push but they stop contracting and they become capable of pulled to their original shape.
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Thus the muscle of the skeleton are found in pairs.one pulls the muscle back to the original position.
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Since they work in direct opposition to each other then they are referred to as antagonistic pairs.
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NB//:-flexor muscles pulls back the bones(tibia-fibula)while the extensor muscles pulls the bones(tibia-fibula)forward
THE HEART,ENERGY AND EXERCISE Myogenic
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The beating of the heart is due to self exciting and therefore it originates from the heart itself and such a stimulation is referred to as myogenic
Intrinsic rhythimicity
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In the early embryo the cells hich are destined to become the heart begin contracting rhythymically long before the actual organ forms and hence they are said to have intristic rhythimicity.
Sketch and label the parts of the heart concerned with electrical activity o f the heart Pg 172 fa
How the cardiac cycle is co-ordinated by the electrical excitations
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On the walls of the right atrium there are special muscles known as sino-atrialnode(SAN) and are referred to as the pacemaker.
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They produce electrical excitations which are spread across the atria(auricles) causing them to contract(atrial systole)
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These excitations stimulate the AVN which is along the septum(line of symmetry of the heart)within the ventricles.
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The excitations are transmitted from AVN through the bundle of HIS(purkyne tissue)into the walls of the ventricles and thereby resulting in their contraction(ventricular systole)and the process is repeated NB//:-the speed at which the excitation spreads through the heart ensures that atria have stopped contracting before the ventricles start.
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The changes in electrical excitations of the heart are measured using an electrocardiogram(ECG) pg 153
Why is the ECG used,placed on the surface of the skin?
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This is because the rhythm of the heart results to spread of a wave of electrical activity(depolarization)through special tissues in the heart.
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This electrical activity causes tiny electrical charges on the surface of the skin.
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An ECG measures these changes that are found on the surface of the skin.
What is the importance of ECG?
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It indicates different heart conditions and thus it monitors patients with heart diseases(CVDS)as they tend to have different ECG patterns
1. Events of the heart beat on the ECG pg 153
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The curve P represents the spread of impulses from the SAN across the atria.
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The curve Q,R,S represent the spread of impulses through the purkyne tissues and over the ventricle.
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The curve T represents the diastole.
Using the ECG below calculate the rate of the heart beat for this individual
Breathing rhythms fa pg115
Components of lung volumes
Tidal volume(TV) -
It is the volume of air that one takes in and out at rest and it is about 500cm3
Inspiratory reserve volume(IRV) -
This is the volume of air that is forcefully taken in after the normal breathing in at rest and it is about 3000cm3
Expiratory reserve volume(ERV)
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It is the extra-volume of air that is given out after normal expiration and it is about 1000cm3
Vital capacity
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It is the sum of TV,IRV and ERV
Residue volume -
this is the volume of air that remains in the lungs after expiratory reserve volume. 1500cm3
Ventilation rate
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This is the measure of the volume of air that is breathed in a minute Ventilation rate=tidal volume x frequency of inspiration per minute Ventilation rate-------------dm/min
How the rate of ventilation is controlled by the respiratory center in the brain (involves negative feedback)
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There are chemoreceptors in the carotid artery and in the aorta which detects the change in concentration of co2 in the blood
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When the co2 concentration increases/decreases the chemoreceptors are stimulated and they send an impulse to the medulla oblongata/respiratory center/ventilation center i.e in the inspiratory center
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The inspiratory center sends impulses to the external intercostals muscles and the diaghphragm mscles which contracts and therefore b rings about inspiration and the volume of the lungs increases.
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Stretch receptors are stimulated which send impulses to the medulla obolongata and switches on the expiratory center but switches off the inspiratory centre.
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The expiratory centre sends impulses to the external intercostals muscles and the diaphragm muscles which relaxes and expiration takes place.
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The volume of the lungs decreases and the stretch receptors are stimulated and an impulse is send to the medulla oblongatai.e inspiratory center which is switched on and the expiratory centre which is switched off.
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The cycle is repeated.
Diagram ex.bk.
Homeostasis
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This is the mantainance of a constant internal environment of the body regardless of the external or internal conditions.
Receptor This is a specialized cell,tissue,an organ which detects changes in the body or the external environment
Effector This is a cell,organ or tissue which responds to a stimulation by the motor nerves and works to reverse a change or increases it.
A sketch diagram showing the principle of negative feedback in maintaining systems within narrow limits.(ex.bk.)Pg 154
Negative feedback system.
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It is a system enabling the body to maintain a condition within a narrow range.e.g if one factor goes up the system changes to bring it down and vice vasa
Positive feedback system.
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It is a system enabling the body to change conditions(increase the effect which was triggered by the response)e,g if one factor goes up the system changes to increase the effect(i.e body mechanism is unable to bring a situation back to normal)
Cardial volume.
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This is the volume of blood pumped out at each heartbeat.
Cardiac output and its importance.
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It refers to the total volume of blood that is pumped in a minute. Cardiac output(dm3/min)= cardiac volume(dm3)xheart rate(beats/min)
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When cardiac rate is high it provides more oxygen and glucose at a higher rate to the tissues especially during exercise.
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It heps in the removal of metabolic waste products such as co2,lactic acid
Heart rate control
(a) By nervous system
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Cardiovascular control centre is found in the medulla oblongata and it controls the rate of the heart beat.
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Chemical and stretch receptors in the lining o f the blood vessels and chambers of the heart sends impulses to the cardiovascular control center once stimulated.
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The nervous control of the heart is by the autonomic nervous system(involuntary) which is divided into two:i.
Sympathetic nervous system which speeds up the rate of the heart beat i.e it is excitatory
ii.
Parasympathetic nervous system which slows down the rate of the heart beat i.e it is inhibitory
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Impulses from the sympathetic nerve from the cardiovascular control center stimulates the SAN and thus increasing the frequency of the signals from the pacemaker and the heart beats more quickly.
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Impulse from parasympathetic nerves inhibit SAN and therefore slows down the rate of the heartbeat
(b)By hormones
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When one is stressed the hormones adrenaline is produced
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This affects the SAN by speedind up the excitation and hence increasing the rate of the heart beat.
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This supplies oxygen,glucose,etc to the muscles,brain,etc and one is able to fight,flee or fly
Heart response when one participates in an exercise
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It involves a negative feedback response to the pressure of blood in the circulatory system.
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As the atria fills with blood(as more blood than usual returns to the heart)due to the squizzing of the big muscles of the legs and arms.
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The stretch receptors in the muscle walls of the heart responds to the stretching by sending enough impulses along the sympathetic nerve to the SAN causing an increase in the heart rate
Baroreceptors involvement in the feedback control of the heart
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Baroreceptors are sensors that are sensitive to pressure
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They are found in the sinuses of the carotid arteries in the neck.
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As the blood pressure in the arteries increases e.g. at the end of an exercise the baroreceptors are stretched.
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They send impulses to the cardialvascular control centre.
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This center then sends impulses through the parasympathetic nerves to slow down the heart rate and widening of the blood vessels(vasodilation) and therefore lowering the blood pressure
TEMPERATURE CONTROL AND EXERCISE Low critical temperature This is the temperature at which the normal thermoregulatory measures to conserve heat are no longer enough and therefore the metabolic rate increases to produce heat(this helps to maintain the core temperature) Low lethal temperature
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This is the temperature below which the chemical reactions of the body can no longer take place fast enough to maintain life and this results to death.
High critical temperature -
This is the point beyond which if the external temperature continues to increase,metabolic rate starts to go up with reactions doubling their rate for every 10oc rise in temperature,hence,positive feedback occurs at high metabolism i.e means more heat production which can lead to death. NB//:- Death usually occurs when the core temperature reaches about 42oc as the enzymes become denatured
Parts of the skin involved in maintaining the core body temperature i.
cold receptors,
ii.
Warm receptors
iii.
Sweat glands
iv.
Erector muscles
Superficial blood capillaries
v.
1. Describe how the core body temperature is maintained constant?
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During thermoregulation two types of receptors are involved i.
Receptors I the skin which detect change in the external temperature(cold and warm receptors)
ii.
Receptors in the brain situated in the hypothalamus which detects temperature in the blood
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When the temperature increases the heat loss center is activated and the heat gain centre is inhibited through nervous communication.
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This inturn,through the autonomic nervous system(involuntary)sends impulses to the effectors such as:i.
Hair erector muscle:- the muscle relaxes and this makes the hair to lie flat o the skin surface and therefore no air will be trapped and hence heat is easily lost to the surrounding by radiation,convention,conduction
ii.
Vasodilation:-
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The sphinicter muscles of the superficial arterioles relax and therefore more blood flows into these capillaries dilating them
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Less blood flows through the deeper shunt vessels pg 165
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As more blood passes near the surface,temperature gradient between the body surface and the environment becomes steeper and heat is lost by conduction,convention and radiation. iii.
Sweating
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The sweatgland becomes active producing more sweat which is removed onto the body surface through the sweat duct.
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The body(skin) provides latent heat of vapourisation and therefore sweat gains the heat and evaporates while the body loses heat. iv.
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Panting
Musclesof the diagphragm and the ribcage may cause panting especially in dogs thus heatloss increases and temperature lowers.
NB//(i)-(iv) are negative feedback mechanisms
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When temperature falls the same receptors are involved.
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The heat gain center is activated which sends impulses to the effectors through autonomic nervous system i.
Vasoconstriction
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The sphincter muscles of the superficial arterioles contract and little blood flows near the skin surface while more flows through the deeper shunt vessels.
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Temperature gradient between the body surface and the environment is less and hence less heat is lost by conduction,convention and radiation. ii.
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The impulse from the heat gain centre stimulates involuntary muscles which begin to contract and relax alternatively and this raises the amount of heat released in metabolism(respiration) iii.
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Adrenaline medulla glands
It brings about production of adrenaline which converts glycogen into glucose which can be used for respiration and therefore more heat is generated. iv.
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Shivering
Erector muscles
They contract causing the hair to stand and trapping a layer of air and being a bad conductor of heat it prevents heat loss. NB// :in human goose pimples are the ones which are formed but standing of hair is evidence in other mammals. v.
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Sweating:-
Sweat glands become inactive,hence no sweat and latend heat of vaporization is conserved. NB/- the response of skin receptors have effects on animal behavior e,g if it is hot some animals may seek for shade or not engage in an activity Animals living in cold areas develop a thick layer of fat which acts as insulator against heat loss. HEAT EXERCISE AND SPORT
Effects of too little exercises
i.
Obesity
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Studies show a strong correlation between levels of exercise in a population and obesity.
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This is because exercise uses up energy.
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The balance between the energy you take in and the energy used can be maintained by regular exercise tends to lead to an excess of energy intake which the body stores as fat and therefefore resulting to obesity. ii.
Diabetes
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There are two forms of diabetes i.e type I and type 11
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Type two developes later in life beyond 40 years. This is due to lack of enough Insulin or the body cells may not respond to insulin that one makes.
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Analysis by the international obesity task force, etc suggest that obesity is a major risk of type II diabetes NB//:- A study done to 3234 overweight people with signs of type II diabetes maintained regular exercise program for about 3 years and reduced the risk of getting type II diabetes by 58%. iii.
Coronary heart diease(CHD)
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Men who increase their level of physical activity have 23% lower mortality than their counterparts who do not exercise.
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Main cause of the death’s is CVDs Effects of too much exercise
a. Suppression of immune system
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Moderate exercise benefits the immune system as the nu mber of upper respiratory tract infection reduces.
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However,athletes in heavy training programmes have shown an increase in respiratory tract infections.
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A theoretical causal link graph is as shown below pg 170
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Analysis of blood from the athletes shows that moderate exercise increases the number of T-killer cells which recognize and destroy pathogens and hence the reduction in respiratory tract infections.
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Intensive exercise lowers the number and activity of T.killers cells,B cells and T. helper cells.
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This reduces the efficiency of the immune system,therefore offering a causal(direct link)mechanism for the impact of intense exercise.
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The psychological build up due to competition causes stress which leads to the production of adrenaline that suppresses inflammation and therefore reducing anti body production.
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Thus it is difficult to determine whether it is stress or exercise that affects the immune system sometimes. Possible explanations for the observed infection rates in athletes
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The participants are in close proximity in the early stages of marathon and hence cold viruses could spread easily.
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Athletes travel wide using aircrafts while alot of people meet a t sporting events and thus increasing chances of transmission. b. Wear and tear on joints 1. Structure of a joint pg 332 fa
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The end of the bones are surrounded by a cartilage which absorbs shock.
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On the surface of the cartilage is the synovial membrane which secretes or produces synovial fluid which reduces friction and therefore allows free movement of the joints.
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Osteo-athritis though not necessarily from excess exercise can cause joint problems.
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The cartilage which reduces friction and cushions the joint becomes roughened and eroded.
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The bone end thickens and the synovial membrane makes more fluid causing the joints to swell and at the same time one experience the pain.
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The cartilage wears away completely and the bone ends meet.
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The bones wear away and thus changing the joint shape and causing severe pain.
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Osteo-athiritis in young people causes swelling of the fluid sacs(synovial cavity) which cushions the joint.
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The swelling presses against other tissues causing inflammation and pain.
How medical technology enables those with injuries and disabilities to participate in sports
i.
Rice
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If diagnosis shows one or more sprained ligaments with no fractured bones then one is given treatment for soft tissue injury between 24-28hrs i.e RICE(rest,ice,compression,elavation)and taking anti-inflammatory pain killers.
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This is done to reduce heat,swelling and protect the joint from further joint damage.
-
If the ligaments are completely raptured the treatment involves a cast to prevent the ankles from moving for about two weeks while compressing and massage continues to reduce any remaining swelling. ii.
Keyhole surgery(arthroscopic menisectomy)
-
The knee has two menisci(cartilage cushions) which are for shock absorption as well as for protecting the underlying bone
-
If MRI scan(magnetic resonance image)formed by combining x-rayed sections of the body to produce a 3d image shows tear to the cartilage then an operation known a keyhole surgery is done to remove the torn part.
-
In this case a fibre optic tube with a small camera and light attached to look inside the knee.
-
Small surgical instruments can be inserted to cut away the torn area and remove it.
-
This is done through a very small incision(cut)around the knee
-
This takes about 10 days with good physiotherapy and the player can continue playing.
-
Before this method,the knee used to be opened up and the whole cartilage removed.
-
Recovery time took months and and at times leads to osteo-athritis and knee joint replacement as the knee were no longer covered by cartilage. ACL
-
It refers to the anterior cruciate ligament and it keeps the knee joint in place.
-
If damaged,then further injuries are likely to happen and the joint may be destroyed.
Forms of ACL treatment
i.
Resting and no surgery
ii.
Reconstructive surgery which involves several techniques e.g i)
Using the patients own patella or hamstring tendons
ii)
Allograft i.e a donated tissue from someone who has died.
(iii) Knee joint replacement using prosthetics:-
-
Prosthetics are artificial replacement for an extension of a body part.
-
It helps the patient to escape pain and disability due to arthritic damage
-
Athletes with permanent disabilities can compete more efficiently at all levels
-
The end of the femur(thigh bone)is replaced with a metal prosthesis while the end of the tibia(shin bone)is replaced by a combination of metal and plastic.
-
Such patients can participate in moderate excercises
2. Limitations of prosthetics
-
Some sports e.g skiing,horse riding.etc are discouraged due to high chances of damaging the knee joint.
-
The joints wear out more quickly if exercises are done frequently
-
The metal and plastic parts may wear loose to the bone they are attached to.
-
Bits of wearing off at the joints may cause inflammation.
PERFORMANCE ENHANCING DRUGS
-
WADA
-
It refers to world anti doping agency which is a body that oversees the battle against the use of performance enhancing substances and techniques.
-
It decides which substance /techniques to be banned
Main groups of substances that have been completely banned
i. -
These are mainly the male sex hormone i.e testosterone that are used for building muscle mass and performance ii.
-
Hormones
They have specific effects e.g erythropoietin(EPO) which stimulates the formation of RBC,growth hormones which affect the muscle growth iii.
-
Anabolic steroids
Beta-2- agonistics
They dilate the bronchioles allowing more air into the lungs NB// Athletes with asthma are allowed to take a certain dose from inhalers iv.
-
Athletes have blood diffusion of their own b lood removed months earlier or donated earlier or artificial oxygen carrying compounds v.
-
Blood doping
Gene doping
These are attempts to change the genetic make up of the cells in order to enhance athletic performance vi.
Diuretics
-
Athletes have to provide urine samples for drug testing.
-
Excess urination eliminates traces of illegal substances before they can be tested . vii.
-
Hormone- agonistics
These are chemicals which mask or change the action of another hormone.
How the performance enhancing drugs work/How genes can be switched on and off by transcription factor including hormones Pg180
1
i.
Anabolic steroids
-
They are closely related to the male sex hormone testosterone
-
The steroid hormones as well as the natural testosterone are able to pass through the cell surface surface membrane.
-
The steroids combine with receptor molecules and they are carried into the nucleus through the nucleus pores where they modify the gene expression(switching on of genes that were previously switched off)
-
The hormone /receptor complex acts as a transcription factor
-
It binds to the DNA switching on particular genes linked to protein synthesis.
-
This changes the MRNA produced which in turn affects the type and numbers of proteins produced including enzymes
-
The hormone stimulates protein synthesis forming.
with bigger and stronger muscles
- NB//:testosterone is broken down in the body and therefore artificial hormones are normally used(because no enzymes that can breakdown the bonds between nadrolone) Disadvantages of anabolic steroids
-
It disrupts normal hormone production and hence it is linked to infertility.
-
There are problems in the menstrual cycle i.e becoming very irregular
-
A drop in sperm production in men and this may lead to impotence
-
They lead to high blood pressure and heart attack
-
Liver damage
-
It raises the level of aggression ii.
Erythropoietin(EPO)
-
It is a peptide hormone which acts as a DNA transcription factor and therefore it switches on a certain gene.
-
This results in the production of enzymes needed for the synthesis of more RBC.
-
They bind to a receptor in the cell surface membrane
-
The membrane bound complex activates a second messenger in the cytoplasm and triggers a protein kinase cascade(this involves activation of several proteins u ntil the final product enters the nucleus and acts as a transcription factor)
-
Erythropoietin is a naturally occuring hormone and popular with athletes and cyclists where it is commonly used. Limitations of erythropoietin
-
-
An excess of RBC thickens the blood and can lead to stroke and heart attack.
Ethical positions relating to whether use of performance enhancing substances is acceptable i)
Creatine phosphate
- Not all substances enhancing performance are banned e,g creatine -
It is naturally found in the muscles as creatine phosphate
-
It is obtained directly from the diet and the body can as well synthesise(make it)
-
Athletes take creatine as supplement and thus increasing their stores and help them when short bursts of high intensity of exercise are n eeded.
-
Hence it is acceptable as a nutritional supplement and not as a drug
- NB// it can cause high blood pressure and kidney damage. ii)
Erythropoietin
-
Use of this hormone to increase RBC is banned.
-
Donating and storing blood to transfuse back to our system just before competition to increase oxygen carrying capacity of blood is also banned.
-
But it is legal for an athlete to train for weeks at high altitude where the body naturally increases RBC to carry more oxygen which is triggered by natural extra erythropoietin secretion.
Completely banned(other substances) 1. Stimulants-increase the heart rate and make you more alert e.g caffeine,cocaine,et.c 2. Narcotics-powerful painkillers e.g heroine and morphine which allows athletes to ignore pain and compete harder Banned in some sports 1. Beta blockers
-
These are drugs which make the heart beat more slowly and reduce any response to adrenaline such as trembling.they are used by athletes who need a very steady head
and are banned in 17 different sports including shooting,darts,gymnastics and the helm in a sailing boat. THE NERVOUS SYSTEM Ex. Bk. Pg 26
Simple systems that make up the nervous system. i.
-
The central nervous system It consists of the brain and the spinal cord.
ii.
Peripheral nervous system
-
It consists of sensory and motor neurons into somatic nervous system(voluntary) and autonomic nervous system(involuntary)
-
The autonomic nervous system is further divided into sympathetic nervous system(which involves spinal nerves only)and parasympathetic nervous system which involves cranial and spinal nerves
Neurones -
Nerves
These are individual cells and each one has a long nerve fibre which carriers the nerve impulse.
-
These are bundles of nerve fibres which are in three groups i)
Motor nerves-they consist of motor fibres
ii)
Sensory nerves-They consist of sensory fibres
iii) Mixed nerves- they consist of motor and sensory fibres
Neuroglia and an example
-
These are cells which provide structural and metabolic support to the neurons e.g Schwann cells
Sketch and label the structure of motor neurone.Fa bk.
1. Describe the structure of the neurons
-
Each neurone consists of the following features
i)
-
Cell body
It contains the nucleus surrounded by granular cytoplasm referred to as Nissl’s granules which consist of R.E.R where the proteins are madei.e the neurotransmitter substances ii)
Cytoplasmic processes/projection a) Dendrites
-
They are highly branched(this increases the surface area for sensitivity)and they carry impulses from receptors and adjacent neurons to the cell body.
-
(b) Axons
It conducts impulses away from the cell body to other neurons or effectors Schwann cells
They are found on the surface on he axon at equal intervals and that from a layer that keep wrapping the axon which is referred to as the myelin sheath. Function of the myelin sheath It insulates the neurons
It allows fast transmission of impulses by making them jump from one node of Ranvier to the next and this is known as saltatory conduction Nb: myelinated axons conduct impulses faster than in one myelinated axons of the same diameter. Name 3 types of neurons depending on the arrangement of dendrites and axons? i.
Multipolar neurones
They have many dendrites branching from the cell body e.g motor neuron. ii.
Bipolar neurons
They have only a single Dendron which arises directly from the cell body opposite the axon. That act as receptors for the senses of site smell etc examples relay neurons.
iii.
Pseudo unipolar neurons
They have a single Dendron with which the axon branches from a common stem called the cell body i.e the cell body is on the side connected via a small branch e.g sensory neurone. Differences between motor and sensory neurone Motor a) Transmits impulses from CNS to effectors e.g muscles
Sensory Transmits impulses from receptors to the CNS
The axons is short b) The axon is long
c) Dendron is very short
Dendron is long
They are pseudo unipolar d) They are multi-polar
e) Cell body at the terminal end Cell body along the middle.
Factors that affects the speed of impulse in neurones i.
The presence or absence of myelins sheath mylinated nerve fibres can transmit impulses much faster than unmyelinated nerve fibres.
ii.
Diameter of the nerve fibres- the thick the fibre the more rapidly impulses are transmitted along ( this is because there is a large surface area fro the exchange of ions between inside and outside the axons membranes)
Terms used in nervous system. •
Polarized : in this case the membranes of the axons on is said to be polarized when the outside has positive ions and inside has negative.
•
•
•
Depolarized this is when the membranes has positive ions inside and negative ions to the outside ( when an impulse is passing)
repolarized – out side is positive and inside is negative after an impulses has passed.
Hyper polarized – this is when the inside of the membranes is excessively negative or the outside is excessively positive.
Resting potential
This is the potential difference maintained by a neurons when not transmitting an impulse (70mv) Action potential
This is the potential difference maintained by a neurones when an impulse is passing through a neurons ( + 40 mv) Ions and their distribution which enables a neuron to maintain resting potential •
•
•
•
The resting potential is due to the difference in concentration of ions across the axo n membranes. The ions include Na+, K+ , CL- and organic anions eg coo Na+ are much greater outside than inside while K+ are much greater inside than outside. Cl- are more concentrated outside than inside while inside ther are cooHow distribution is maintained
•
The organic ions i.e coo- have no gates ( channels) and hence they remain inside throughout.
•
A few K+ move out by diffusion but some remain as they are attached by coo- inwards and since the inside is negatively charges they are repelled.
•
Na+ concentrated is high outside but the permeability for it is low ( few channels)
•
Any sodium ions that enter are captured by ions pump and expelled to the outside. What happens in the neurone when an impulse passes through it?
•
•
More Na+ channels open and therefore enters in Na+ enter faster then they are pumped out by the ions pump.
•
The permeability of the membranes to Na+ decreases as the channels close.
•
This is followed by an increase in permeability of K+ as more channels open.
•
This allows K+ ions to flow out and the potential difference inside decreases to its negative value.
•
K+ channels remains open and there is a slight K+ overshoot which causes the membrane potential to become slightly lower than its normal resting value ( - 70Mv)
•
This is known as hyperpolarisation
•
During the passage of the nerve impulse the axons has gained Na+ and lost K+ ions.
•
These ions are re-exchanged by Na-K pumps which actively pump Na+ out and K+ inside.
Stimulus threshold: •
This is the point at which sufficient Na channels open for rush of Na+ into the axons to be greater than the outflow of K+ ions
Nb: once the threshold has been reached the action potential occurs regardless of the stimulus intensity. •
•
This is the period of time following an action potential when nerve fibre cannot be re stimulated at all.
Relative refractory period
This is the time during refractory period when the axon can be restimulated only if the stimulus is stronger than usual (the threshold is much higher) Synapse
This is a gap that is found between one neurons and the next. Sketch and label the fine details of a synapse Ex bk pg 31
How an impulses passes across the synapse •
When the action potential reaches the synaptic knob calcium channels open and therefore Ca 2+ move in.
•
This causes the synaptic vesicle to move towards the presynaptic membranes.
•
They fuse with it and then breaks open and by exocytosis the acetylcholine ( transmitter substance ) is released
•
Acetylcholine diffuses through the synaptic cleft onto the receptor on the post synaptic membranes.
•
This causes the membranes to become permeable to Na+ and hence causing depolarization.
•
This causes a change in the potential difference across the membrane and excitatory post synaptic potential (EPSP) is formed.
•
Suffucient EPSP exceeds the threshold value and an action potential is set up which is transmitted along the post synaptic neuron.
NB in some cases the neurotransmitter has opposite effects whereby different ions channel open allowing inward movement of negative ions and therefore an inhibitory post synaptic potential (IPSP) results.
The post synaptic membrane then produces an enzyme referred to as acetyl cholinesterase which breaks down acetyl choline which then diffuses back into the synoptic knob. Energy from the mitochondria combines them together forming acetyl choline which goes back into the synaptic vesicles and can be used again. Different forms of transmitter substances a) Acetyl choline
It is synthesized in the synaptic knob and the nerves which use it as their transmitter substance are called cholinergic nerves. b) Nor adrenaline
It is mainly found in the sympathetic nervous system and the nerves which use it as their transmitter are referred to as adrenergic nerves. c) Dopamine
It is only found within the CNS How drugs/poison affect the synapse a) Nicotine
It has similar effects to acetylcholine (it mimics) at the synapse by hav ing an excitatory effects on the post synaptic neuron. In large concentration nicotine can block transmission after initial transmission. b) Curare
It is used on arrow tips by the Sothern America Red Indians It interferes with the action of acetyl choline and stops depolarization of the synaptic membrane and this therefore causes paralysis as the muscles can no longer be stimulated by the nerve. c) Organo phosphorous compounds e.g weed killers, insecticide, nerve gases.
They inactivate cholinesterase at the post synaptic membrane thus preventing breakdown of acetyl choline. This prolongs the effects of acetylcholine as it is no t broken down and the nerves fire continuously and the muscles are sent to tetanus. Evidence that transmission across the synapse is chemical and not electrical
1.) By use of electron microscope the synaptic cleft has been found to be 20nm which is too wide for an impulse/action potential to jump across. 2.) Electron micrographs taken after a nerve has been strongly stimulated for sometime shows lack of synaptic vesicles and this is an evidence that all the transmitter substance has been used up. 3.) A variety of drugs/poison interfere with the working of synapse showing that the substance that are transmitted are chemicals.
INTERACTION BETWEEN NEURONES: Spatial summation pg 210
This refers to when two or more synaptic kno bs are stimulated and releases neurotransmitter substance at the same time onto the same post synaptic membranes and therefore triggering an action potential which would not have been achieved by a single synaptic knob.
Temporal summation
This refers to when impulses are received in pre-synaptic knob in quick succession and the rapid repeated release of neurotransmitter triggers an action potential in the post synaptic nerve fibre.
It involves facilitation whereby the first impulse does not trigger a response but makes it easier for the passages of the next impulse. Accommodation / fatigue This is the process by which the response is lost as all the neurotransmitter substance is discharged from the vesicles of the synapse as result of repeated stimulation. The response returns once more when the transmitter is synthesized.
The two types of sensory receptors that are found invertebrates in terms of receiving stimulus and converting it into an impulse
a) Prim Primar ary y rece recept ptor ors. s. This is when a simple sensory receptor where a stimulus result directly in an action potential in the nerve fibre of the neurons e.g e .g pressure receptors in the skin. b) Secondary receptors.
This involves a sensory receptor cell which responds to a particular stimulus and then synapses with a sensory neuron triggering an action potential in that nerve fibre which carried ca rried the impulse to the CNS. Receptors.
The different forms of sensory receptors a) Exteroceptors: They respond to stimuli outside the body. b) Interoceptors: They respond to stimuli inside the body c) Chemoreceptors: They are sensitive to chemical stimuli eg smell, taste, PH, etc... d) Mechanoreceptors: They are sensitive to mechanical stimuli eg movement, pressure, tension, etc… e) Proprioceptors: They are sensitive to the relative position of the skeleton and the degree of muscle contraction and therefore they maintain posture.
How receptors work i.
They work by forming generator current cu rrent which is a small current that is set up in a receptor on reception of stimuli due to the movement of Na+ into the receptor.
ii. ii.
Generat Generator or potent potential ial-- this this is what what is prod produce uced d in respons responsee to gener generato atorr current current in in the sensory receptor cells.
NB Small stimuli result to a small generator potential potential while large stimulus results to large generator potential and therefore generator potential does not obey all or nothing law. The above can be summarized as follows. Stimulus potential
local change in permeability action potential.
generator current
generator
Convergence and its importance
This is when several sensory receptors synapse with a single neurons. It is important as it is an adaption of increasing sensitivity of a sensory system to a low level e.g in the retina cells (rods) Adaptation and its importance
This refers to when a sensory receptor is exp osed to a steady stimulus whereby it shows gradual g radual decline in the generator potential produced and hence the action potential in the sensory neuron becomes less frequent and may eventually stop. This is known as adaptation. Its importance is that it prevents the nervous systems from carrying unnecessary impulses and therefore frees the CNS from irrelevant information e.g. i.
Unpleasant smell rapidly becomes tolerant.
ii. ii.
Hot Hot bath bath feel feel comfo comfort rtabl ablee aft after er some someti time me
THE EYE ex. Pg 35. Photoreceptors in the retina
Rods Cones The structure of the retina fa bk.
It is made up of 3 layer of cells. a) Out Outermo ermost st photore photorecept ceptor or layer layer
It contained rods and cones which are partly embedded in the pigmented epithelial cells of the choroid. b) Inter Interme media diate te middle middle layer layer
It consist of bi-polar neurons which have synapses with rods ad cones in the photoreceptor p hotoreceptor layer and also with the ganglia cells ce lls in the inner layer. c) The inner layer called called the internal internal surface surface layer layer which which contains contains the ganglia ganglia cells cells and axons of the optic nerve. Structure of a rod cell pg 35
a) Ribo ibosome some::
It is the site for protein sysnthesis i.e the pigments (rhodopsin) b) Mitochondria It provides energy in form of ATP for protein synthesis c) Cilia
They flick to and fro and therefore helps in the movement of rhodopsin into the outer segment (membranes) d) Memb embranes
They provide a large surface area for the attachment of the pigment (rhodopsin) and also provide a large area for trapping light from the objects. Transducers
These are structures which can convert one form of energy into another eg and rods convert light energy into electrical energy of the nerve impulse
Pigments that are found in the rods and cones •
Rhodopsin in the rods
•
Iodopsin in the cones How light energy is converted into electrical energy in the impulse
•
Rhodospsin consist of a protein that is called opsin (combination of a lipid and protein) which is combined with retinal which is derivative of vitamin A
•
Retinal can exist exist in two forms forms a) Cis retinal
b) Trans-retinal •
•
•
•
•
In the dark it is all in the Cis form Light (photons) from an object causes Cis retinal to change to trans retinal which has a different shape and can no longer bind tightly to the opsin and hence breaks down into retinal and opsin and this is known as bleaching. Bleaching of rhodopsin changes the permeability of the cell membranes of the rod cell to sodium ions which are normally very permeable p ermeable and now becomes less permeable. However sodium pump continues to work at the some rate pumping Na+ out of the cell. This increase the negativity inside the rod cell. Hence an action potential is generated which causes an impulse to be transmitted along the bipolar neurons.
NB: the initial stimulus in the rod cell causes hyper polarization instead of depolarization depolarization as the outer segment has a decrease in permeability to Na+ while in the inner segment Na+ are being pumped out by active transport and the rod cell become increasingly negatively charged. This hyper polarization is what is known a s generator potential. Why one see darkness temporarily when one enters into a room from a brightly lit area •
•
Rhodopsin breaks down rapidly in bright light and hence there is not much of it stored in the rods. Therefore rhodopsin has to be resynthesized using energy from a ATP to convert the trans-retinal back to as Cis retinal but this takes time and therefore one sees unclear/blurred images
•
Due to this the rods are almost entirely bleached and no longer respond to dim light and the eye is said to be light adapted
•
When the rods of the eye have recovered after a period in the dark, all the rhodopsin will be fully reformed and the eye will be more sensitive to dim light and the eye is said to show dark adaption.
Q
difference between rods and cones
Rods •
•
Cones The outer segment is cylindrical The membranous vesicles are not formed from the infolding of the outer membranes
•
•
The outer segment is cone shaped Membranes vesicle are formed from the infolding of the outer membranes
• •
•
They are sensitive to light of low intensity The rods contain a visual pigment known as rhodopsin
•
•
•
Not sensitive to light of low intensity They contain the visual pigment iodipsin which is thought to occur in 3 different forms a) Responding to red light
•
b) Responding to blue light
c) Responding to green light According to trichromatic theory of colour vision, different colour are[received by the degree of stimulation of each type of cone by the light reflected from the objects. •
•
They are Many rods well distributed in the retina but none in the fovea
Do not from accurate images as several rods synapse with one bipolar cell
COORDINATION AT WORK: Reflexes
•
•
There are fewer cones in the retina but a very high concentration of cones in the fovea. They from more accurate images as each cone synapse with one bipolar cell.
•
These are fast, fixed, unconscious responses to a particular stimulus
NB: if they involve the brain than they are called cranial reflexes. The role of iris as an effector and its importance •
•
•
It consist of two sets of muscles i.e circular and radial. It controls the amount of light entering the eye e.g in bright light the radial muscles relax while the circular muscles contract and this reduced the size of the pupil which in turn reduces the amount of light entering the eye which would otherwise damage the delicate rods and cones by over stimulating them. The opposite takes place in dim light.
Q Explain how the nervous system or organism can cause effectors to respond as exemplified by pupil dilation / contraction or describe the pupils reflex action?Pg 219 •
Light enters one or both of the eyes at the same time
•
Light falling on the sensory cells of the retina causes impulses to travel along the optic nerve to the brain.
•
The brighter the light, the bigger the frequency of action potentials
•
This is detected by the control centre in the mid-brain
•
•
•
•
•
Impulses then travel along two neurones to further control centre of which is for the other eye The nerve impulse then synapses which branches of the parasympathetic cranial nerve ( occulomotor nerve) which transmit the impulses to the iris Effectors are stimulated i.e the radial muscles relax, circular muscles contract and the pupil reduced in size. If frequency of action potentials from the retina falls (light level d rops) then the impulses from the control centre along sympathetic nerves to the iris causes circular muscles to relax and radial muscles to contract. This negative feedback system controls the amount of light entering the eye.
NB Adrenaline hormones produced during stress causes the pupil to widen ensuring that one can use all the available light to see as well as possible.
Pupil dilates when you see someone you like or physically attracted but constricts when you see someone you don’t like or not attracted. Reflex arc •
This is the path followed by an impulse from the receptor to effector.
•
Stimulus
Receptor
Synapse
Sensory Neurons Via Dorsal Root
Relay Neurons
Neurons Via Ventral Roots
Synapse
Motor
Effectors
SENSITIVITY IN PLANT Stimulus to which plants respond a) Light •
Its direction
•
Intensity of light ( stomata close or open)
•
Length of daylight ( affect flowering) b) Gravity c) Temperature d) Touch
e) Chemicals
NB Different parts of the same plant may react differently to the same stimulus e.g shoots and roots to light. How Plant grow pg 38 ex bk
•
Growth is a permanent increase in size of an organism or part of it.
•
It is normally brought about by sell division cell elongation etc
•
The main areas of cell division and elongation in plant are known as meristems.
•
These are areas just behind the tip of a root or shoot.
•
•
These are the main areas of growth in plant and they are sensitive to chemicals messages produced in response to a variety of stimulus These chemicals messages seems to make it easier for cellulose cell wall to be stretched.
Effects of light . Importance of light to plants
a) To provide energy for photosynthesis ( to excite the electrons) b) It is required as a stimulus before germination can occur ( BREAKING dormancy) c) It controls the opening and closing of the stomata. d) It affects the time of flowering in many plants depending on the day length ( photoperiod) e) It is required in the formation of chlorophyll
f) It influences the direction of plant growth e.g if a plant is in the dark and there is light coming in a given direction. Effects of darkness to plant a) Plant grow rapidly using up the food reserved. b) The plant appear yellowish white as chlorophyll does not develop c) The stem elongate more rapidly than normal and they are thin and fragile.
d) The leaves remain small and the tips of the stem remain in hooked position. Such plants are said to have etiolated
e) Once the plant reaches the light, growth slows down and the leaved turn green as chlorophyll is formed
Effect of far red and red wavelength on germination of lettuce seeds •
Batches of seeds were soaked in the dark.
•
They were exposed to alternating periods of red and far red light.
•
The germination percentage was then determined No germination x 100 Total no. of seeds
•
Each period of exposure to light lasted for 5 minutes.
•
The following were the results
Treatment
% germination
Red
70
Red/ far red
6
Red / far red/ red
74
Red/far red/ red/ far red
6
•
From the above the wavelength of light to which the seeds were last exposed has the greatest effects on % germination
•
Red light (600-700mm) promotes germination while far red (720-760mm) inhibits germination
•
If the seeds were exposed to red light for 5 minutes followed by another 5 minutes of far red light is cancelled by that of far red light.
•
From this experiment the scientist hypothesized that a plant pigment reacts with the different types of light and in turn affects the response of the plant.
•
This pigment was isolated from plants and it is called phytochrome.
Phytochrome and its effects
•
They are blue green pigments and are present in very small quantities in the leaves / plumule
•
Their colour is masked by chrolophyl
•
It exists in two inter convertible forms i.e Pr and PFR
•
PR is also known as P660 as it absorbs light of wavelength 660mm
•
PFR is also known as P720 as it absorbs light of wavelength 730 nm.
•
When Pr absorbs red light it is converted to PFR.
•
When PFR absorbs far red light it is converted to Pr.
•
Exposure to natural daylight on a sunny day is equivalent to exposure to red light and thus there will be more PFR to Pr in plant.
•
•
•
PFR is converted slowly to Pr in the dark. presence of phytochromes may stimulate the production of other growth regulate plant hormones which bring about the response to light. i.e Plant hormones eg auxins
How phytochromes are involved I etiolation •
In the dark there is plenty of PR but no PFR
•
Thus PFR seems to inhibit the lengthening of the internodes ( Pr promoted lengthening of internodes)
•
It stimulated both the formation of chlorophyll and expansion of leaves.
•
Thus without PFR internodes grow but the leaves do not and no chlorophyll is formed
•
PFR
_
germination takes place
Critical day length0
This is the length of day light which appears to be needed to trigger flowering in plants ( it is approximately 14 hrs) Long day plants
These are plant which flower when the no. of hrs of daylight exceeds the critical value ( 14hrs) eg cabbage, wheat, spinach etc.
Short day plants
These are plants which flower when the day length is below critical value ( 14hrs) eg beans, tobacco, strawberry etc Day neutral plants
Flowering is not affected by daylength eg tomato, maize, cucumber etc Sketch a graph to show the % of pant that flower against daylength of the 3 types of plant named above. Pg 41 ex
How flowering is related to the length of the dark period ; show this with the help of bar diagrams
Roles of the phytochrome during flowering in longday plants and short day plants
1 The daylength is long i.e more than 14hrs and the night is short. The PR obtained during the day is converted to PFR PFR is slowly converted to PR during the night.
Since the night is short the PFR concentration left would be high This is the cause of flowering in LDP (LDP required high concentration of PFR for flowering) 2) Exposing long day plant to a short period of darkness during the day has no effect on the flowering as the conversion of PFR to PR is slow. 3) The night is long and much of the PFR is converted to PR and therefore only small amount would be left and hence flowering in SDP requires low concentration of PFR.
4) The night is interrupted with light (PR) •
This is immediately converted to PFR and hence there is an increase in PFR which results to flowering in LDP
From the above it can be concluded that the length of the period of darkness is the environment cue or factor affecting flowering and not the daylength. photoperiod detection •
It takes place in the leaves of the plant where florigen (hormones) is made in response to changing levels of phytochromes (PR and PFR)
•
It is carried in the plant transport system to the flower buds.
evidence for transportation of florigens •
•
If the whole plant is kept in the dark apart from one leaf exposed to the appropriate periods of light and dark flowering occurs as normal but if kept in total darkenss no flowering takes place. If a photo periodically exposed leaf is removed immediately after the stimuli, it does not flower but if removed after a few hrs it flowers.
3) If two or more plants are grafted together and only one leaf is exposed to appropriate light patterns, then all the plants will flower.
Florigen formation •
•
When a leaf is exposed to a given amount of light and dark a particular form of MRNA is produced in the leaf. This MRNA is linked to a gene associated with flowering ( the FT gene or flowering locus)
•
The MRNA can move from one cell to another through the transport tissues and then through the plasmodesmata to the apex of the shoot where other genes associated with flowering are activated and thus FT MRNA looks as if it is the florigen
Role of phytochromes and florigen in flowering plant pg 42 ex. Bk
TROPIC RESPONSES IN PLANTS tropism and examples
This is the growth movement of the plant or part of it towards or away from a stimulus e.g a) Phototropism
This is the growth movement of a plant / shoot towards light from one direction and this allows absorption of maximum light for photosynthesis. b) Geotropism
This is the growth movement towards the force of gravity. Root show positive geotropism and helps them to obtain mineral salts and water from the soil. c) Chemotropism
This is the growth movement towards or away from chemicals eg growth of pollen tube towards the embryo sac. d) Thigmotropism
This is the growth movement due to touch stimuli. experiment to show positive phototropism •
A potted plant is placed in a box with an opening on top of one side.
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Light rays are allowed to pass through the hole from one side (unilateral light)
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After a few days the shoot of the plant bends towards the source of light and thus showing positive phototropism
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A control experiment is done using a clinostat i.e the potted plant is placed on a clinostat which rotates (I revolution per hour) and hence all the part of the shoot are exposed to light equally.
experiments to show that bending of a shoot depends on some chemicals substances. (messages)
A variety of experiments can be done, some of which includes the following
a) A shoot of a plant is grown in the dark
b) If the tip is removed decapitated)
c) A tip of the shoot is removed (decapitated) and then replaced again.
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From the three experiments it can be concluded that the tip of the shoot exerts an influence on the region of growing cells behind it
d) A razor blade is inserted to the shoot behind the tip as shown below.
e) A tip of a shoot growing in the dark is removed and placed on an agar block and left fro several hours. •
The agar block is then placed on the cut end of the shoot.
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A chemical is produced at the shoot tip which diffuses into the agar block and then diffuses into the rest of the shoot stimulation normal growth.
f) A tip of the shoot growing in the dark is decapitated and placed on agar.
After several hours the block is placed asymmetrically on the decapitated shoot.
NB all the above experiments are referred to as went bioassay Unilateral light and phototropism: effect of unilateral light to the shoot tip ( chemical substance)
A tip of the shoot is cut and placed on an agar block which is divided. After sum hours the blocks were placed on some decapitated tips asymmetrically.
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From all the above experiments the message that is the chemical substance is the plant hormone ( plant growth, substance) i.e auxins
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Auxins are powerful growth stimulants and effective in very low concentrations eg indole acetic acid (IAA)
Draw a diagram to show the shoot as it would appear after several hours?
Q
describe the mechanism that caused the change you have drawn.
How auxins work •
IAA is made in the tip of the shoots
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It diffuses back to the area of cell elongation
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The molecules if IAA binds to specific receptors on the cell surface membranes activating the active pumping of hydrogen ions into the cytoplasm
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This concentration of hydrogen ions provides the optimum PH for the enzymes which break the bonds between adjacent cellulose micro fibris and hence keeps the walls flexible. The cell absorbs water by osmosis and the flexible cell wall stretched allowing the cell wall to expand. As the cell matures IAA is destroyed by enzymes, the PH of the cell wall rises and the bond formed between the cellulose micro fibrils. The cell walls becomes rigid and can no longer expand.
NB light causes auxins to move to the dark side where concentration increases. This then stimulated cell elongation on the dark side and hence moe growth takes palce resulting to bending of the shoot towards light. •
Research shows a link between phytochromones and bith geotropism and phototropism eg phototropism in very young shoots can not take palce until phytochromones have been activated Compare and contrast the mechanism of coordination in plant and animals
Animals •
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Chemicals control is relatively slow but long lasting The hormones are carried around the body by plasma in the circulatory system. E.g. (adh – pituitary gland – kidney – nephron – collecting duct) or (adrenaline – adrenaline gland – heart ) Hormones move into the target cell by diffusion and they are picked up by receptors sites on the cell membranes. They control growth and sexual maturity response to stress and blood sugar levels e.g adrenaline, testosterones , estrogen
Plant •
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They work in very low concentration e.g. florigen responsible for flowering in plant Hormones move in the transport system of plant i.e. phloem and by diffusion between cells
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They allow long term response to environmental changes.
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Chemicals control is often linked to changes involving the growth of an organism
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Hormones can be used as control mechanism such as negative feedback system eg auxins (IAA) florigen, gibberellins
NB plants do not have electrical coordination but animals have which consist of nervous system with conducting nerve cells. •
it controls rapid response to stimuli eg reflexes
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it allows coordination of many nervous inputs allowing learning to take place.
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Sometimes it has long term changes related to memory.
Give the differences between coordination in plants and animals. Plants
Animals
THE BRAIN Describing the simple structure of the simple nervous system of the vertebrates •
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It develops as a hollow tube of nervous tissue that forms the spinal cord. It contains grey matter made up of the neurons cells bodies and white matter insisting of the nerve fibres. At the anterior end of the vertebral embryo the tube swells forming the fore brain, mid and hind brain. Depending on the animal the forebrain folds back over the entire brain with specific functions concerned with major senses. location and the functions of the different parts of the brain
a) Cerebrum / cerebral hemisphere •
It is found in the fore brain.
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It is made up of almost entirely the grey matter as it consist of nerve cell bodies dendrites and synapses.
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The cerebral cortex is a thin layer but it is highly folded to give a large surface area.
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The left and the right cerebral hemispheres are connected by axons ( white matter known as corpus collasum)
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The left side of the cerebrum controls the right side of the body and vice versa.
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It is divided into a number of lobes as explained on the next page.
a) Frontal lobe •
It is concerned with emotional response planning ahead reasoning, decision making etc.
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It is the conscious areas of the brain which combines information from several parts of the cortex to develop ideas.
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It is linked to ones personality
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It contains the primary motor cortex of the brain which controls body movements.
b) Temporal lobe •
It is involved in processing auditory information i.e sound recognizing , hearing speech. Etc.
c) Occipital lobe ( visual cortex. •
It process visual information i.e seeing shape recognition colour vision etc.
d) Parietal lobe •
It is associated with some aspects of memory and recognition
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It is the area concerned with the ability to calculated with movement and sensation.
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It is concerned with the ability to orientate oneself in space.
ii) Hypothalamus •
It is located in the fore brain
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It coordinates autonomic nervous system.
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It concerned with thermoregulation of the bod y.
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It control hormone secretion by the pituitary gland.
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It controls many basis drives e.g. thirst ( osmo regulation,) hunger, aggression and reproductive behaviour.
iii) Cerebellum •
It is found in the hind brain
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It coordinates smooth movement.
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It uses information from the muscles and the posture.
iv) Medullar oblongata •
It is found in the hind brain and it contains reflex centres which controls function such as heart rate, blood pressure, breathing rate, coughing, sneezing, swallowing , peristalsis etc.
How the brain works evidence of how the brain works
There are a number of sources which can be used i.
Animal studies
There are number of approaches. a) By observing now the brain develops and then placing obstacles in the way of that development. b) By damaging or removing areas of the brain and observe the effects on its behaviour e.g. cerebral hemisphere from dogs, monkeys etc. c) Observation of normal behaviour and learning can be made compared with post mortem change in the brain.
NB it is not ethical to use animals as some communities attach value to animal.
However , the results obtained are used to improve human life, especially people affected by brain diseases and damage. ii.
Studying Human Brain.
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Experiment interfering with or damaging the brain are not carried out since it not ethical.
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However, it can be done when brain surgery patient have allowed their brain to be artificially stimulated.
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Conscious patient describe the sensations relating to the stimulation and this has shown that certain areas of the brain are association with particular function. A lot of information is from situation where parts of the brain are damaged or missing from birth or as a result of illness. Diseases affecting the brain can cause serious problems to people affected but can help scientist to know now the health brain and hence possible treatment
iii.
Medical imaging technology (MIT)
a) X – rays •
They are used for taking images of hard tissues e.g. bones and hence they are less useful for producing images of soft tissues like the brain.
b) Computerized tomography (CT Scan) •
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It allows scientist and doctors to see the inside of the body e.g. through the head. It involves thousands of tiny beams of x-rays passed through an area of the body. E.g. head
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Each bean is reduced in strength (attenuated) by density of the tissue it passes through.
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X rays which make it through are detected and measured.
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All of the data are put together in a computer to produce a cross section image of a thin slice through the body
NB some special dyes are injected into the blood or tissues to make a particular area x-ray opaque so that they show more clearly in the scan. A CT scan identifies i.
Major structure in the brain e.g. cerebrum
ii.
Detects problems such as brain tumours
iii.
Bleeding in the brain ( strokes)
iv.
Swelling of arteries in the brain ( aneurism)
The images formed are like photographs and hence cannot show how areas of the brain are used, however evidence from CT scan images are linked to observed changes in behaviour and can indicate importance of certain areas of the brain. C
magnetic resonance imaging (MRI- scan) •
They produce images using magnetic fields and radio waves with much finer details than Ct scans of the soft tissue.
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This removes the risks of damages from the X-rays that are used in CT scan.
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Hydrogen atoms are the most commonly imaged element because.
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Much of the body is made up of water
ii.
Hydrogen atoms produce strong MRI signals
The signals produce are analyzed by a computer and used to produce an image. How MRI scan is produced
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The patient is placed in a strong magnetic field and all the protons CH+ are aligned before this the protons spin at random. A pulse of rf (radio frequency) magnetic field o scillations is applied and this causes the protons to rotate in place.
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The rf pulse is then turned off
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The protons still rotate in phase and induce MRI signal.
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The signal is amplified and analyzed and by this time protons start to return to normal
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An image of the respond differently to the magnetic field depending on the amount of water in the structure or tissue.
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Hence distinct regions of the brain can be recognized in the image.
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Thin sections of the body are usually examined and they produce 2D MRI scans.
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The computer can put these sections together to produce a 3D image. MRI produce very detailed images which give doctors a great deal of information when compared to CT scan.
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D
It is used to diagnose brain injuries, stroke, tumours and infection of the brain or the spinal cord. By showing up areas of damage in the brain very clearly it has enabled doctors to make links between the structures in the brain and pattern of behaviour seen in their patients functional magnetic resonance imaging (FMRI).
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It makes it possible to watch the different areas o f the brain in action while people carry out different tasks e.g. FMRI monitors the uptake of oxygen in different parts of the brain Deoxyhaemoglobin absorbs the radio waves signals and later re emits it while oxyhaemoglobin does not.
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Action active area of the brain has a high blood flow and more oxyhemoglobin is delivered to supply the active cell with oxygen and thus areas of the brain absorb but re emit less energy than less active areas.
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FMRI give an extremely spatially image of the brain.
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It is used to investigate normal brain structure and functions
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Currently researchers are looking at ways of using FMRI to diagnose diseases eg early signs of strike and onset of Alzheimer
drawbacks of FMRI
a) It is a noisy procedure and some people find it very stressful b) It is carried out with the patient head remaining completely still as nay movement reduced accuracy of the image. QEEG ( Qualified Electro Encephalography) •
It is a device used in brain mapping techniques.
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It is uses sensors attached to the outside of the skull to measure the activity of the brain as the patient carried out different activity.
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This allows scientists to build up map indicating which areas are used in different activities and skills.
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Its major disadvantage is that it is not as spatially accurate in the brain as FMRI
NATURE AND NURTURE IN BRAIN DEVELOPMENT factors that affect brain development
i) Genes that are inherited (nature) ii) Getting the right environmental stimuli (nurture) critical windows
- These are periods of time during which vital natural connections are made in the brain in response to a specific stimuli. - Absence of such stimuli ensures that the right pathways are not developed normally. NB. This has been investigated using the development of the visual cortex in animals such as monkeys, ferrets. how the visual cortex (capacities) develop due to nature
During foetus development axons from light sensitive cells in the retina grow to the thalamus (next to hypothalamus) where synopses are developed in a regular way resulting to an orderly arrangement of neurons in the visual cortex. •
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Stained sections of the visual cortex show columns of cells called acular dominance. Neighbouring columns of cells receive input from the same area of the retina in the left eye and the right eye. •
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These columns are already present in the visual cortex at birth and this is as a result of genotype (nature)
evidence that columns are present at birth •
Two scientists i.e Crowley and katz injected new born ferrets with radio active traces in the eyes.
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They moved from one eye and were found in specific bands in the visual cortex.
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This shows that ocular dominance columns are present at birth.
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Other scientists i.e Horton and Hocking delivered three foetal monkeys by caesarian section and 8 days before gestation period (time from conception / fertilization to birth)
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They were kep completely in the dark throughout in their lives.
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A radioactive tracer was injected into the right eye of each monkey one day after they were delivered.
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A week later sections of the visual cortex were prepared and they showed ocular dominance columns.
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The above experiments of H & H showed that they are present at birth and hence genetically inherited (nature)
how the visual cortex / capacities are affected by the environment Nurture / Critical window •
Kittens and monkeys are used as they have visual cortex similar to humans
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Some experiments were done by Hobal and Weisel regarding critical window for the development of visual cortex.
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They stitched shut (satured) one or both of the eyes of the infant kittens and monkeys.
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The age when satured and deprived off vision, and the length of time they remained closed was varied.
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Some other animals were reared in the dark and in the light environments and the effects of these treatments on visual cortex were measured and the results were as follows.
i) Kittens whose eyelids were satured at 1 weak old (before the eyes had opened) could see perfectly well with their open eye (other eye)
After one to three months the closed eye was opened and the other eye stitched. The kittens were blind as they banged into things a fell off steps and tables. The eye showed no physical signs of blindness but, recording from the visual cortex showed very few cells were firing nerve impulses. •
The same results were obtained with monkeys.
ii) When one eyelid is closed in a cat of 4 months which could see normally until then had no effect on recordings made in the visual cortex.
iii) In kittens the period of susceptibility is between 4 – 5 weeks after birth.
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Closing an eye for 3 – 4 days has a profound effect on the number of neurons which fire in the linked areas of visual cortex.
iv) Critical period for development of visual cortex in monkeys is between 6 – 8 weeks after birth. How the visual cortex develop after birth •
In a new born kitten, monkey or humans, there is considerable overlap between the dendrites and synapses of axons in different columns.
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In adults there is less overlap and this suggests the change is due to the visual experience.
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Axons compete for target cells in the visual cortex.
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Action potential passes along the axon and arrive at a target cell where they release the neurotransmitter substance from the synapse.
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If another neurone also synapses with the same target cell but no impulses pass along it then no transmitter substance is released and eventually synapses not firing will be weakened and destroyed. This reduces the no. of unwanted axons and synapses and makes sure messages / impulses are carried efficiently to exactly where they are required
methods used to compare the contribution of nature and nurture to brain development. •
Research has been carried out on primates and thus increasing the likelihood that humans will have a similar critical window when external stimuli are crucial.
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Information from experiments done on kitten and monkeys may be unethical on human beings, hence the need for more evidence to compare the relative inference/ conclusion of nature and nurture is needed which is normally done indirectly e.g.
i) Individuals with damaged brain.
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It is thought that neuron connections of the cortex that controls voluntary movement speech and reasoning became fixed after a certain stage. After brain damage due to stroke, accidents etc there is a current evidence suggesting new connections may be made which by pass the damaged area with a different part of the brain taking over the function.
ii) Using new born babies
1. Observations made by doctors when treating new born babies shared more light on the interaction of nature and nurture on brain development e.g babies born with cataract (cloudly lenses which limit the amount of light reaching the lens) in one or both eyes.
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If removed when the child is very young, sight develops normally but if surgery is left until the child is older, sight cannot be restored suggesting that a critical cortex in humans and this pattern also reflects the development seen in young monkeys and kittens hence confirming the usefulness of that research.
2. Another study shows that babies as young as 2 days recognize the difference between a living biological organism and a non-biological movement.
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Using light patterns recorded from joints and random light patterns, new born infants show that they could discriminate between the two different patterns of motion.
They preferred biological movements ( as they kept their attention much longer and looked much longer at biological display which were the right way up that up than upside down.
The biological movement shown to infants was from chicken. This biological movement discrimination has been in a number of animals like chicks, cats, monkeys, pigeons, apes, dolphins etc and thus showing in brain development nature appears to be important.
3. Further research suggests.
i) Genetic tendency towards face recognition ii) There is a critical window of brain development when we learn to distinguish human faces from others •
As babies gain experience of looking at faces, one area of the cerebral cortex becomes sensitive to the types of faces they see most but lose ability to distinguish less familiar types of faces such as monkeys.
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Further experiments show younger babies are better than older ones at recognizing faces of different monkeys but all babies could distinguish between different human faces.
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Thus there seems to be some level of critical window around 6 months of age when ability to recognize faces narrows down.
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Adults who work with monkeys and apes soon learn to distinguish them by their face alone.
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All this shows interaction between nature and nurture in development of different parts of the brain.
iii) Twin studies and face recognition •
Using FMRI, the activity of the visual cortex of 24 sets of fraternal and identical twins was measured.
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The twins were presented with several sets of images e.g houses, letters strung together and people’s faces.
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Scrambled images that could not be recognized were used as base line measurement (control).
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Analysis of the brain activity patterns from the identical twins were more similar that those from fraternal twins when looking at faces and places.
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Response patterns to words and letters show little difference between the two types of twins.
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The results suggest a strong genetic basis for response to faces and places but less genetic link for words/letters and therefore stronger environmental impact (nurture)
iv) Cross cultural studies -
When objects less than 30cm away from the eye are observed then the same object is seen from two different angles.
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In the visual cortex two images are super-imposed to give a 3D images.
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Far objects will not show a 3D
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The brain therefore uses other clues from the surrounding and past experience to give you the depth of perception.
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Hence one can tell the difference between a cow that is far away and the toy cow nearby.
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The images of the cows may be much the same size but other close and life experience means that you know one animal is big and far away and the other is big and close to you.
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The clues and cues (factors) used for depth perception are unconscious and we depend on them during challenges such as optical illusions.
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This is when differences between people raised in different cultures emerge suggesting that brain development that gives us distance perception is due to our environment (nurture) examples
i) Muller – Lyer illusion: Many people in UK see line Y longer although they are the same length with X.
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Zulu people (South Africa) rarely misjudge length o f lines and this is due to cultural differences.
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In UK people live in carpentered world full of straight lines, right angles, corners and rectangular buildings.
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Hence, line and angles are interpreted as if they belong to a rectangular room as this is the pattern laid down as the brain develops and hence, Y looks larger that X.
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Zulu people have circular culture where their homes are circular and there are few straight roads and lines.
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These scientists believe they do not have ‘hard wired’ interpretation of line patterns and hence they rarely misjudge, and therefore, perception of distance is strongly affected by environmental experiences.
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Other scientists have put forward a hypothesis that difference in perception are due to differing levels of retinal pigmentation which in turn affects the ability to detect contours.
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People with heavier retinal pigmentation are less good at detecting contours and so are less likely to be illusioned.
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This would explain the Zulu ability to judge the length of the line correctly.
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Other studies back up the idea of critical window when depth perception develops.
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For example, in a study it was found that very young children from most cultures find it difficult to judge distances in a picture.
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They would be likely to say that the boy was pointing to the tractor.
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By the age of 11 most European children interpreted distance cues (factors) correctly.
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Some 11 years old African children from particular cultures and non-literate adults from Europe or Africa are less likely to pick up due the cues to the perspective of the picture due to probably lack of experience.
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This therefore suggests that visual depth perceptions are learned as the brain develops if the right environmental cues are in place.
LEARNING AND MEMORY types of behaviour i) Innate or species characteristic behavior
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It is a large collection of responses which are usually seen in every member of a particular species.
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Behavior is not learned and hence it is a genetically determined response to a particular stimulus.
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It occurs as specific nerve pathways are laid down in the embryo from the instructions of the DNA.
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Examples are courtship behavior, territorial display etc.
- Nature is completely dominant in the development of these neuro pathways in the brain -
It is important to non-vertebrates which are normally short lived and have no time to learn by trial and error if they have to successively complete their lifecycle.
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Invertebrates instinctive behavior is important in young ones which have no time to learn trial and error while in adults ready made responses to a given situation leaves higher areas of the brain free for more complex learned behavior
ii) Learned behavior (Individual Characteristics)
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Learned behaviours occurs due to experience e.g a child touching a hot oven door whereby the hand is withdrawn rapidly due to reflex.
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The child is unlikely to touch the oven door again.
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Learned behavior can be classified into the following groups.
1. Habituation: This is learning to ignore a stimulus and make no response when the stimulus is repeated many times with no apparent reward or punishment associated with it e.g.
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Humans living near railway lines or road links sleep without constant awakening in response to noise stimuli.
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The way the birds learn to ignore scare crow.
2. Conditioned reflexes
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This is the association of a particular stimuli with an existing unco nditional reflex e.g Parlor’s dogs – during lunch time he would first ring the bell and provide the dogs with food which made them to salivate.
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One day the bell rang but no food was provided but the dogs still salivated.
3. Trial and error operant learning. -
This is learning which occurs when a piece of behaviour is either rewarded or punished and therefore becomes more or less frequent as a result.
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If the animal associates the outcome of a behaviour, it is likely to be repeated.
4. Imprinting -
This is the learning which occurs in young animals when they identify and relate strongly to another organism usually the parent.
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If no parent is available, other large moving objects can be identified with.
5. Exploratory (latent) learning
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This is the learning which takes place when an individual explores new surroundings or experience without immediate punishment or reward.
6. Insight learning
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This is the learning based on thought and reasoning which often involves problem solving.
HABITUATION how animals including humans can learn habituation
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This experiment is done using nermatode worms or the giant sea slug A plysia.
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A plysia breathes using gills that are found in a cavity on the upper side of the body with water pass through.
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The water is expelled through a siphon tube at one end
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If this siphon is touched, the whole gill is withdrawn into the cavity as a defence mechanism.
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Sea slugs live in the sea and water current constantly sitmulate the siphon and thus animals learn by habituation not to withdrawn gills due to water current/waves.
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A plysia can be reared in the laboratory where there are no waves of water movement.
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Under these conditions the siphon was stimulated with a jet of water and the gills were withdrawn and thus the animal habituated.
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This was retained over time showing that it was not a case of accommodation.
mechanism of Aplysia experience
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The neurons involved in gill reflex were identified and investigations carried out.
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It was noted that the calcium channels are in the presynaptic membrane and the synapse becomes less responsive with repeated stimulations.
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Hence, fewer calcium ion channels open and fewer calcium ions cross into the pre synaptic knob and thus fewer vesicles move to the presynaptic membrane discharging neurotransmitter substance.
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Less transmitter substance binds to the receptors on the pa st synaptic membrane and the post synaptic excitatory potential (PSEP) is not high enough to trigger an action potential and hence there is no response.
Humans
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It is an important form of short or long term learning e.g if you visit someone living near a railway line, the first few times a train passes, one would be aw are due to the noise produced.
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After a few hours you will no longer notice the train i.e you become habituated.
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If you don’t visit again for sometime your awareness of the trains passing will be re-instated but you will habituate more rapidly on your second visit.
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New born babies have a number of startle reflexes which habituate as the baby matures and are lost completely e.g more reflex where a baby arches and throws its arms up and out in a grasping movement if it is startled or its head is lowered suddenly.
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These responses fade away in a normal baby within 8 weeks of birth allowing them to interact more calmly with the world around them.
NB. Modern research suggests that one of the problems for people affected by schizophrenia may be that they do not habituate as readily as other people.
BRAINS, GENOME AND MEDICINE neurotransmitter substances found in the brain
NB. Imbalance of this neurotransmitter substances can result in both mental and physical symptoms.
Why is it difficult to treat diseases caused by imbalances o f transmitter substances?
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It means getting the drugs across the blood brain barrier
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The barriers are formed by endothelial cells lining c apillaries of the brain as they are tightly joined
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This makes it difficult for bacteria to cross to the brain cells.
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However, it is also difficult to get therapeutic drugs into the brain.
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Drugs affecting the brain are usually active at the synapse and they target various stages in synaptic transmission.
stages at the synapse affected by drugs (either by curing a problem or causing one) 1) Neurotransmitter synthesis and storage in the vesicles 2) During the release of the transmitter substance 3) In the neurotransmitter receptor binding site 4) During the process of re uptake of constituents of transmitter substance 5) Breakdown of transmitter substance.
effects of parkinson’s disease that is brought about by dopamine. -
It involves loss of nerve cells in an area of the mid brain known as substantia nigra
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These cell produce dopamine and their axons spread through out the frontal cortex, spinal cord and so on and hence they are concerned with the control and coordination of movement.
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These nerve cell die and motor control is gradually lost
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For along time the brain compensates for the loss
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It mainly develops in people of 50 years though it can appear in young people
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The causes are not clear although in young people there appears to be a strong genetic link although it is very rare
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In common parkinson’s disease genetic link is much weaker and other factors e.g toxins, herbicides and pesticides seem to play a part.
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Symptoms don’t show until around 80% of their dopamine producing cells are dead
symptoms of parkinson’s diseases (due to falling levels of dopamine) include:
i) tremor (shaking) : which usually starts in one hand; the forst symptom for around 70% of the affected people ii) slowness of movement: i.e. it is hard to get started to a movement, and the movement take longer to perform. iii) stiffness (rigidity) of muscles: whereby one finds it difficult to turn over in bed or stand up after sitting.
As the disease progresses other problem arises e.g. poor balance, difficulty in walking, problem with sleeping, speech breathing and depression.
It mainly develops in people over 50 years though it can appear in young people.
Causes are not clear although in young people though very rare there appears to be a strong genetic link. In common Parkinson’s disease genetic link is much weaker and other factors e.g. toxins, herbicides, pesticides, seems to play a part.
What are the effects of drugs on synaptic transmission in treatment of Parkinson’s disease.
Currently there is no cure for Parkinson’s disease bu t some drugs ease or delay the symptoms by replacing the natural dopamine in the brain or allow the body to make the best use of the dopamine it still produces -
Treatment of the symptoms include:
i) Levodopa (l-dopa)
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Dopamine cannot cross the blood brain barrier thus cannot be used to treat Parkinson’s symptoms
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However L-dopa is a precursor of dopamine which can cross the barrier
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It makes the remaining cells to make as many much dopamine as possible.
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This relieves stiffness and slowness of movement, but finally becomes less effective as brain cells continue to die
ii) Dopamine agonists
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These chemicals bind to dopamine receptors in brain synapses and mimic effect of dopamine
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They are used at the beginning of the disease when they are most effective.
iii) MAOB inhibitors (monoaminoxidase B)
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MAOB is an enzyme which breaks down dopamine in the brain synapses.
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MAOB inhibitors inhibit the enzyme reducing the destruction of any little dopamine that is made.
Other ways of curing Parkinson’s
i) Gene therapy:
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Although Parkinson’s disease is not a genetic disease, scientists are investigating the possibility of inserting healthy genes in the affected cell by:
a) Adding genes to prevent the dopamine producing cells of mid brain from dying b) Adding genes to enhance the levels of dopamine production in the remaining cells.
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However there are major problems in delivering healthy genes to cells of midbrain and safety must be of prime concern.
ii) Stem cells therapy:
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This aims at providing cure for Parkinson’s disease rather than therapy to relieve symptoms.
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The embryonic stem cells are likely to replace the falling dopamine producing cells.
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Current research using mouse models are promising but are ethical issues of using embryonic cell remains
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There is a risk in using stem cells that is uncontrolled growth and hence cancer may result.
Note: As scientists stimulate embryonic stem cells to become dopamine producing cells, this will give them a chance to develop more effective drug therapies.
How does depression come about?
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Causes of depression are complex and are not fully understood, but one cause may be problems with neurotransmitter substance i.e. serotonin in the brain.
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Serotonin is the transmitter substance in a group of cells in the brain stem which have axons spreading into cortex, cerebellum and spinal cord.
