Unit 3.6 Organisms respond to changes in their natural and external environment

Question 1

what are receptors? and effectors?

Answer 1

they detect stimuli, they can be cells or proteins on cell surface membranes.
effectors are cells that bring about a response to a stimulus, to produce an effect

Question 2

what are the three neurones?

Answer 2

1- sensory = transmits electrical impulses from receptors to the CNS
2- motor = transmits electrical impulses from CNS to effectors
3- relay = transmit electrical impulses between sensory neurones and motor neurones

Question 3

describe the path of an stimulus?

Answer 3

its detected by receptor cells and an electrical impulse is sent along a sensory neurone. when the impulse reaches the end of a neurone, neurotransmitters send an impulse. the CNS processes the info and send impulses along the motor neurone

Question 4

what does the autonomic system divide into?

Answer 4

the sympathetic nervous system and the parasympathetic system

Question 5

what is a reflex?

Answer 5

its where the body responds to a stimulus without making a conscious decision to respond, info travels really fast from receptors to effectors.

Question 6

what are the advantages to reflexes?

Answer 6

• simple reflexes help organisms to protect the body because they’re rapid
• neurotransmitters are quickly removed, so their response is short lived
• when an impulse reaches the end of a neurone, neurotransmitters are secreted directly onto target cells

Question 7

what is a tropism?

Answer 7

the response of a plant to a dirrectional stimulus. plants respond to stimuli by regulating their growth.

• a positive tropism is growth towards towards the stimulus
• a negative tropism is growth away from the stimulus

Question 8

what is phototropism?

Answer 8

the growth of a plant in response to light.

• shoots are positively phototropic and grow towards light.
• roots are negatively phototropic and grow from light

Question 9

what is gravitropism?

Answer 9

the growth of a plant in response to gravity.

• shoots are negatively gravitropic and grow upwards
• roots are positively gravtropic and grow downwards

Question 10

what do plants respond to?

Answer 10

they respond to directional stimuli using specific growth factors - these are hormones - chemicals that speed up or slow down plant growth. they are produced in the growing regions of the plant and they move to where they’re needed in the other parts of the plant

Question 11

what are growth factors?

Answer 11

they are auxins that stimulate the growth of shoots by cell elongation, where the cell walls become loose and stretchy so the cell gets longer. high concentration of auxins inhibit growth in roots

Question 12

what is Indoleacetic acid (IAA)?

Answer 12

its an auxin that’s produced in the tips of the shoots in flowering plants. IAA is moved around the plant to control tropisms, it moves by diffusion and active transport over short distances and via the phloem over long distances.
= this results in different parts of the plant having diff concentrations of IAA

Question 13

how does IAA concentration affect phototropism?

Answer 13

• it increases on the shaded side, cells elongate and the shoot bends towards light.
• in the root the IAA increases on the shaded side also, growth is inhibited so the root bends away from light

Question 14

how does IAA concentration affect gravitropism?

Answer 14

• in shoots, it increases on the lower side so cells elongate and it grows upwards
• in roots, it increases in concentration of the lower side so growth is inhibited and it grows downwards

Question 15

what happens when a receptor is in its resting state?

Answer 15

there’s a difference in charge between the inside and the outside of the cell, this is generated by ion pumps and ion channels, there is a voltage across membranes due to it
- the potential difference when a cell is at rest is called resting potential

Question 16

what happens when a stimulus is detected?

Answer 16

the cell membrane becomes excited and becomes more permeable, allowing more ions to move in and out of the cell, altering the potential difference.
- the change in potential difference due to a stimulus is the generator potential

Question 17

what is an action potential?

Answer 17

if the generator potential is big enough it will generate an action potential which is an electrical impulse along a neurone.
- an action potential is only triggered if the generator potential reaches a certain level called the threshold level.

Question 18

what is the pacinian corpuscle?

Answer 18

they are mechanoreceptors, that detect mechanical stimuli eg pressure and vibrations and they are found in the skin

Question 19

decribe the pacinian corpuscle?

Answer 19

it contains the end of a sensory neurone, a sensory nerve ending. the sensory nerve ending is wrapped in loads of layers of connective tissue called lamellae.

Question 20

what happens when the pacinian corpuscle is stimulated?

Answer 20

1- when pressure is applied, it becomes deformed and the membrane around its neurone becomes streched
2- this streching widens the sodium channels in the membrane and sodium ions diffuse into the neurone
3- the influx of sodium ions changes the potential of the membrane, it becomes depolarised, producing a generator potential
4- this creates an action potential that passes along the neurone to the CNS

Question 21

how does the process of electrical activity start in the heart?

Answer 21

it starts in the sanatrial node (SAN), which is in the wall of the right atrium. the SAN sets the rhythem of the heartbeat by sending all regular waves of electrical activity to the atrial walls
- this causes the right and left atria to contract at the same time

Question 22

what prevents the electrical activity from being passed?

Answer 22

a band of non-conducting collagen tissue prevents the waves of electrical activity from being passed directly from the atria to the ventricles. these waves are passed from the SAN to the atrioventricular node AVN

Question 23

what is the AVN responsible for?

Answer 23

passing the waves of electrical activity onto the bundle of His. there’s a slight delay before the AVN reacts, to make sure the atria have emptied before the ventricles contract

Question 24

what is the bundle of His?

Answer 24

its a group of muscle fibres responsible for conducting the waves of electrical activity between the ventricles to the apex of the heart. the bundle splits into finer muscle fibres in the right and left ventricle walls, called the purkyne tissue

Question 25

what does the purkyne tissue do?

Answer 25

it carries the waves of electrical activity into the muscular walls of the right and left ventricles, causing them to contract simultaneously from the bottom up

Question 26

what does the SAN do?

Answer 26

generates electrical impulses that cause the cardiac muscle to contract. the rate at which the SAN fires is unconsciously controlled by a part of the brain called the medulla oblongata

Question 27

what are baroreceptors?

Answer 27

they are pressure receptors in the aorta and carotid arteries

Question 28

what are chemoreceptors?

Answer 28

they are chemical receptors in the aorta carotid arteries and the medulla. they monitor the oxygen level in the blood and also carbon dioxide and pH

Question 29

what happens when there is high blood pressure?

Answer 29

baroreceptors detect high blood pressure. impulses are sent to the medulla, which sends impulses along parasympathetic neurones. these secrete acetylcholine (a neurotransmitter, which binds to receptors on the SAN. the effector is the cardiac muscle and slows the heart rate down to reduce blood pressure back to normal

Question 30

what happens when there is low blood pressure?

Answer 30

baroreceptors detect low blood pressure. impulses are sent to the medulla, which sends impulses along the sympathetic neurones. these secrete noadrenaline which binds to the receptors on the SAN. the effector is the cardiac muscle and speeds up the heart rate to increase blood pressure back to normal

Question 31

what happens when there is high blood O2, low CO2 and high pH levels?

Answer 31

chemoreceptors detect chemical changes in the blood. impulses are sent to the medulla which sends impulses along the parasympathetic neurones. these secrete acetylcholine, which binds to receptors on the SAN. the effector is the cardiac muscle and decreases the heart rate to return O2, CO2, and pH levels back to normal.

Question 32

what happens when there is low blood O2, high CO2 and low pH levels?

Answer 32

chemoreceptors detect chemical changes in the blood. impulses are sent to the medulla which sends impulses along the sympathetic neurones. these secrete noadrenaline, which binds to receptors on the SAN. the effector is the cardiac muscle and increases the heart rate to return O2, CO2, and pH levels back to normal.

Question 33

what is the outside of the membrane like of a neurone?

Answer 33

it is positively charged compared to the muscle, this is because there are more positive ions outside the cell than inside. the membrane is polarised where there’s a potential difference. the voltage at resting potential is 70mV.

Question 34

what is the resting potential created and maintained by?

Answer 34

the sodium potassium pumps and potassium ion channels

Question 35

what does the sodium potassium pump do?

Answer 35

it uses transport to move sodium ions out of the neurone, but the membrane isn’t permeable to sodium ions, so they can’t diffuse back in. this creates a sodium ion electrochemical gradient, because there are more positive sodium ions outside than inside the cell.

Question 36

after an action potential why can’t a neurone cell membrane be excited again?

Answer 36

it cant be excited again straight away because the ion channels are recovering and they can’t be made to open. Sodium ion channels are closed during repolarisation and potassium ion channels are closed during hyperpolarisation. this period of recovery is the refractory period

Question 37

where does light enter?

Answer 37

through the pupil. the amount of light that enters is controlled by the muscles of the iris. light rays are focused by the lens onto the retina, which lines the inside of the eye

Question 38

what does the retina contain?

Answer 38

photosensitive photoreceptor cells which detect light. the fovea is the area of the retina where lots of these are found. the nerve impulses from the photoreceptor cells are carried from the retina to the brain by the optic nerve, which is a bundle of neurones.

Question 39

what is the blind spot?

Answer 39

it is where the optic nerve leaves the eye, there aren’t any photoreceptor cells, so its not sensitive to light.

Question 40

what happens when light enters the eye? 1

Answer 40

it hits the photoreceptors and is absorbed by the light-sensitive optical pigments. light bleaches the pigments, causing a chemical change, and alternating the membrane permeability to sodium ions

Question 41

what happens when the generator potential is created in the eye? 2

Answer 41

if the generator potential created reaches the threshold, a nerve impulse is sent along a bipolar neurone, bipolar neurones connect photoreceptors to the optic nerve, which takes impulses to the brain

Question 42

what are rods?

Answer 42

they are mainly found in the peripheral parts of the brain, they give information in black and white (monochromatic vision)

Question 43

what are cones?

Answer 43

they are found together in the fovea and give information in colour (trichromatic vision). there are three types of cones, red sensitive, green sensitive and blue sensitive

Question 44

describe rods sensitivity to light?

Answer 44

rods are v sensitive to light. this is because many rods join one neurone so many weaker generator potentials combine to reach the threshold and trigger an action potential

Question 45

describe cones sensitivity to light?

Answer 45

cones are less sensitive than rods. this is because cones join one neurone so it takes more light to reach the threshold and trigger an action potential

Question 46

describe rods visual activity?

Answer 46

rods give low visual activity as many rods join the same neurone, which means light from two points close together can’t be told apart

Question 47

describe cones visual activity?

Answer 47

cones give high visual activity as cones are closer together and one cone joins to one neruone. when light from two points hits two cones, two action potentials (one from each cone) go to the brain - so you can distinguish two points that are close together as separate points

Question 48

what is a wave of depolarisation?

Answer 48

when an action potential happens, some of the Na+ions enter they diffuse sideways. this causes Na+ ion channels in the next region of the neurone to open. this is a wave of depolarisation. the wave moves away from the parts of the membrane in the refractory period as these parts cant fire an action potential

Question 49

what does the refractory period act as?

Answer 49

once an action potential has been created of an axon, there is a period afterwards when inward movement of Na ions is prevented as the sodium voltage-gated channels are closed. during this time its impossible for a further action potential to be generated. -> refractory period.

Question 50

what is the all or nothing response?

Answer 50

once the threshold is reached, an action potential will fire. if the threshold isnt reached, an action potential wont fire, this is the all or nothing nature. a bigger stimulus wont cause a bigger action potential, but it will cause them to fire more frequently as all action potentials fire with the same change in voltage.

Question 51

what is the myelin sheath?

Answer 51

its an electrical insulator. in the peripheral nervous system, the sheath is made up of a type of cell called a shwann cell.

Question 52

what is the nodes of ranvier?

Answer 52

betweem the schwann cell, there are tiny patches of bare membrane called the nodes of ranvier, this is where the sodium ion channels are concentrated.

Question 53

where does depolarisation occur in a myelinated neurone?

Answer 53

it only happens at the nodes of ranvier, where sodium ions can get through the membrane.

Question 54

what is saltatory conduction?

Answer 54

the neurone’s cytoplasm conducts enough electrical charge to depolarise the next node, so the impulse ‘jumps’ from node to node. this is saltatory conduction and is v fast

Question 55

where does an impulse travel in a non-myelinated neurone?

Answer 55

it travels as a wave along the whole length of the axon membrane. so you get depolarisation along the hole length of the neurone. this is slower that saltatory conduction

Question 56

how does axon diameter affect speed of conduction?

Answer 56

action potentials are conducted quicker along axons with bigger diameters as there’s less resistance to the flow of ions than in the cytoplasm of a smaller axon. with less resistance, depolarisation, reaches other parts of the neurone cell membrane quicker

Question 57

how does temperature affect speed of conduction?

Answer 57

the speed increases as the temperature increases too, because ions diffuse faster. the speed only increases up to 40 degrees, after this the proteins begin to denature and the speed decreases

Question 58

what is a synapse?

Answer 58

it is the junction between a neurone and another neurone or a effector and a neurone. the tiny gap between the the cells at a synapse is called the synaptic cleft.

Question 59

what is the presynaptic neurone?

Answer 59

it has a swelling called a synaptic knob. this contains neurotransmitters.
- when an action potential reaches the end of a nuerone, it causes a neurotransmitter to be released into the synaptic cleft, they diffuse across the post synaptic membrane and bind to specific receptors.

Question 60

what happens when neurotransmitters bind to receptors?

Answer 60

they might trigger an action potential. as the receptors are only on the postsynaptic membranes, synapses makes impulses unidirectional.

Question 61

why are neurotransmitters removed from the cleft?

Answer 61

so the response doesnt keep happening. they’re taken back into presynaptic neurone and broken down by enzymes

Question 62

what is part 1 of cholinergic synapse?

Answer 62

1- an action potential arrives at the synaptic knob of the presynaptic neurone. the action potential stimulates voltage gated calcium ion channels in the neurone to open. calcium ions diffuse into the synaptic knob

Question 63

what is part 2 of the cholinergic synapse?

Answer 63

2- the influx of calcium ions into the synaptic cleft causes the synaptic vesicles to move to the presynaptic membrane where they fuse with the membrane. the vesicles release the neurotransmitter acetylcholine (ACh) into the synaptic cleft in exocytosis.

Question 64

what is part 3 of the cholinergic synapse?

Answer 64

3- ACh diffuses across the synaptic cleft and binds to the specific cholinergic receprots on the postsynaptic membrane. this causes sodium ion channels in the postsynaptic neurone to open

Question 65

what is part 4 of the cholinergic synapse?

Answer 65

4- the influx of sodium ions into the postsynaptic membrane causes depolarisation. an action potential on the postsynaptic membrane is generated if the threshold is reached

Question 66

what is part 5 of the cholinergic synapse?

Answer 66

5- ACh is removed the synaptic cleft so the response doesn’t keep happening. it’s broken down by an enzyme called acetylcholinestrase (AChE) and the products re-absorbed by the presynaptic neurone and used to make more ACh.

Question 67

what are excitatory neurotransmitters?

Answer 67

they depolarise the postsynaptic membrane, making it fire an action potential if the threshold is reached.
- eg acetylcholine is an excitatory neurotransmitter at cholinergic synapses in the CNS - it binds to cholinergic receptors to cause an action potential

Question 68

what are inhibitory neurotrasnmitters?

Answer 68

they hyperpolarise the postsynaptic membrane (make the pd more negative), preventing it from firing an action potential.
- eg acetylchline is an inhibitory one at cholinergic synapses in the heart. when it binds to receptors there, it can cause k+ ion channels to open on the postsynaptic membrane, hyperpolarising it

Question 69

what happens when a stimulus is weak?

Answer 69

only a small amount of neurotransmitter will be released from a neuron into the synaptic cleft, this might not be enough to excite the postsynaptic membrane to the threshold level and stimulate an action potential.

Question 70

what is summation?

Answer 70

it is where the effect of a neurotransmitter released from many neurones is added together

Question 71

what is spatial summation?

Answer 71

in which a number of different presynaptic neurones together release enough neurotransmitter to exceed the threshold value of the postsynaptic neurone. they trigger a new action potential

Question 72

what happens if some of the neurones in spatial summation are release inhibitory transmitters?

Answer 72

the inhibitory transmitters are negative so the total effect of all the neurotransmitters might be no action potential.

Question 73

what is temporal summation?

Answer 73

in which a single presynaptic neurone releases neurotransmitter many times over a short period. if the concentration of neurotransmitter exceeds the threshold value of the postsynaptic neurone, then a new action potential is triggered.

Question 74

what is a neuromuscular junction?

Answer 74

its a synapse between a motor neurone and a muscle cell. neuromuscular junctions use the neurotransmitter acetylcholine which binds to cholinergic receptors called nicotinic cholinergic receptors.

Question 75

what do neuromuscular junctions have?

Answer 75

their postsynaptic membrane has lots of folds that form clefts. these clefts store the enzyme the break down ACh. it also has more receptors than other synapses

Question 76

what is ACh like at a neuromuscular junction?

Answer 76

it is always excitatory, so when a motor neurone fires an action potential, it normally triggers a response in a muscle cell,

Question 77

what are the first two ways drugs affect transmissions?

Answer 77

• some are the same shape as neurotransmitters so they mimic their action at receptors, so more receptors are activated
• some block receptors so they cant be activated by neurotransmitters, so fewer receptors are

Question 78

how do drugs affect enzymes in transmission?

Answer 78

• some inhibit the enzyme that breaks down the neurotransmitter, this means there are more transmitters in the synaptic cleft to bind to receptors and they’re there for longer

Question 79

how do drugs affect neurotransmitters in transmission?

Answer 79

• some stimulate the release of them from the phagocyte from the presynaptic neurone so more receptors are activated, whilst others inhibit the release if neurotransmitters from the presynaptic so fewer receptors are activated

Question 80

what is skeletal muscle?

Answer 80

its the type of muscle you use to move, they are attached to bones by tendons. ligaments attach other bones to bones, to hold them together

Question 81

what are atagonistic pairs?

Answer 81

muscles that work together to move a bone are atagonstic pairs. the contracting muscle is said to be the agonist and the relaxing muscle is called the antagonist

Question 82

what do pairs of skeletal muscle do?

Answer 82

they contract and relax to move bones at a joint. the bones of the skeleton are in-compressible (rigid) so they act as levers, giving the muscles something to pull against

Question 83

what are biceps and triceps?

Answer 83

the bones of your lower arm are attached to a bicep muscle and tricep muscle by tendons. the biceps and triceps work together to move your arm as one contracts the other relaxes

Question 84

what happens when your bicep contracts?

Answer 84

• when your bicep contracts your tricep relaxes. this pulls the bone so your arm flexes (bends) at the elbow, the bicep is the agonist and the triceps are the antagonist

Question 85

what happens when you tricep contracts?

Answer 85

when your tricep contracts your bicep relaxes. this pulls the bone so your extends (straightens) at the elbow. here, the triceps is the agonist and the biceps is the antagonist

Question 86

what are skeletal muscles made up of?

Answer 86

large bundles of long cell, called muscle fibres. the cell membrane of muscle fibres is called the sarcolema.

Question 87

whats the sarcoplasm?

Answer 87

its the muscle cell’s cytoplasm, where bits of sarcolema fold inwards across the muscle fibre and stick into the sarcoplasm. they fold and are called transverse T tubules and they help spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre

Question 88

what is the sarcoplasmic reticulum?

Answer 88

its a network of internal membranes that run through the sarcoplasm. it stores and releases calcium ions that are needed for muscle contraction.
- muscle fibres also have lots of mitochondria to provide the ATP that’s needed for muscle contraction

Question 89

what are myofibrils?

Answer 89

they are long, cylindrical organelles which are made up of proteins and are highly specialised for contraction. muscle fibres are also multinucleate

Question 90

what are the myofilaments that myofibrils contain?

Answer 90

• thick myofilaments, consisting of long rod shaped tails are made of protein called myosin
• thin myofilaments, consisting of two strands twisted around one another are made of protein called actin

Question 91

what do myofibrils look like under a microscope?

Answer 91

• dark bonds contain thick myosin filaments and light bands contain thin actin filaments. the thick bands are A-bands and the thin bands are called the I-bands

Question 92

what are sarcomeres?

Answer 92

myofibrils are made up of short units called sarcomeres. the ends of each sarcomere are marked with a z-line.

• in the middle of each sarcomere in on an M-line, which is the middle of the myosin.
• around the M-line is the H zone which only contains myosin filaments

Question 93

how do sarcomeres contract?

Answer 93

myosin and actin filaments slide over one another to make sarcomeres contract, the simultaneous contraction of sarcomeres means the myofibrils and muscle fibres contract, the sarcomeres return to their original length as the muscle relaxes

Question 94

what happens in contracted sarcomeres?

Answer 94

the A-band stays the same length, the I-band gets shorter and H-zones get shorter and sarcomeres get shorter

Question 95

what do myosin filaments have?

Answer 95

they have globular heads that are hinged, so they can move back and forth. each myosin head has a binding site for actin and binding site for ATP

Question 96

what do actin filaments have?

Answer 96

they have a binding sites for myosin heads, called actin-myosin binding sites. another protein called tropomyosin is found between actin filaments, it helps myofilaments move past each pther

Question 97

what happens in a resting (unstimulated) muscle?

Answer 97

the actin-myosin binding site is blocked by tropomyosin. therefore myofilaments cant’t slide past each other because the myosin heads can’t bind to the actin-mypsin binding site on the actin filaments

Question 98

what is part 1 of muscle contraction?

Answer 98

when an action potential from a motor neurone stimulates a muscle cell, it depolarises the sarcolemma. depolarisation spreads down the T-tubules to the sarcoplasmic reticulum which causes it to release stored calcium ions into the sarcoplasm

Question 99

what is part 2 of muscle contraction?

Answer 99

calcium ions bind to a protein attached to tropomyosin, causing the protein to change shape. this pulls the attached tropomyosin out of the actin-myosin binding site on the actin filament, which exposes the binding site, allowing the myosin head to bind

Question 100

what is part 3 of muscle contraction?

Answer 100

the bond formed when a myosin head binds to the actin filament is called the actin-myosin cross bridge. calcium ions also activate the enzyme ATP hydrolyse which hydrolyses ATP to provide energy needed for muscle contraction

Question 101

what is part 4 of muscle contraction?

Answer 101

the energy released from atp causes the myosin head to bend, which pulls the actin filament in a rowing action. another ATP molecule provides the energy to break the actin-myosin cross bridge, so the myosin head detaches from the actin filament after its moved

Question 102

what is part 5 of muscle contraction?

Answer 102

the myosin head then reattaches to a different binding site further along the actin filament. a new actin-myosin cross bridge is formed and the cycle is repeated, many cross bridges form and break, pulling the actin filament along, which shortens the sarcomere causing the muscle to contract

Question 103

what happens when muscles aren’t stimulated?

Answer 103

calcium ions leave their binding sites and are moved by active transport back into the sarcoplasmic reticulum using energy from the hydrolysis of ATP too. this causes the tropomypson molecules to move back so they block the actin-myosin binding sites again

Question 104

why aren’t muscles contracted?

Answer 104

no myosin heads are attached to actin filaments so there are no actin-myosin binding sites again. the actin filaments slide back to their relaxed position, which lengthened the sarcomere

Question 105

describe ATP in anaerobic respiration?

Answer 105

ATP is made rapidly by glycolysis. the end product of glycolysis is pyruvate, which is converted to latate by lactate fermentation. lactate can build up in th muscles and cause muscle fatigue. its good for short periods of hard exercise

Question 106

how is ATP made in the phosphocreatine system?

Answer 106

ATP is made by phosphorylating ADP, adding a phosphate group taken from PCr. PCr is stored inside cells and the ATP-PCr system generates ATP. PCr runs out after a few seconds so its used during short bursts of vigorous exercise. the atp-PCr system is anaerobic and its alactic, so doesn’t form lactate

Question 107

describe slow twitch muscle fibres?

Answer 107

1- muscle fibres that contract slowly
2- muscles you use for posture
3- good for endurance activities
4- cant work for a long time without getting tired
5- energy released slowly through aerobic respiration, lots of mitochondria and blood vessels supply O2
6- reddish in colour as they’re rich in myoglobin

Question 108

describe fast twitch muscle fibres?

Answer 108

1- muscle fibres that contract very quickly
2- muscles you use for fast movement
3- good for short bursts of speed and power
4- get tired very quickly
5- energy is released quickly through anaerobic respiration using glycogen, few blood vesserls and mitochondria
6- whitish in colour as they dont have much myoglobin

Question 109

what is taxis?

Answer 109

it is a simple response whose directions is determined by the direction of the stimulus. as a result, organisms respond directly to a environmental changes by moving its whole body either towards or away from a stimulus

Question 110

what is kinesis?

Answer 110

it is a form of response in which the organism does not move towards or away from a stimulus. instead it changes the speed at which it moves and the rate at which is changes direction.

Question 111

what are the two major divisions in the nervous system?

Answer 111

• the central nervous system CNS is made up of the brain and spinal cord
• the peripheral nervous system PNS is made up of pairs of nerves that originate from either the brain or the spinal cord

Question 112

what is the peripheral system divided into?

Answer 112

• sensory neurones = carry impulses from receptors towards the CNS
• motor neurones = carry impulses away from the CNS to the effectors

Question 113

what is the motor neurone system divided into?

Answer 113

• the voluntary nervous system which carries impulses to body muscles and is under voluntary (conscious) control
• the autonomic nervous system which carries impulses to glands, it is unvoluntary (subconscious)

Question 114

what is the sympathetic and parasympathetic nervous system?

Answer 114

• sympathetic stimulates effectors and so speeds up any activity.
• parasympathetic inhibits effectors and so slows down any activity.

Question 115

describe a neurone?

Answer 115

A. cell body - which contains the usual cell organelles
B. dendrons - extensions of the cell body which subdivide into smaller branched fibres called dendrites which carry impulses towards the body
C. axon - single long fibre that carries impulses away from the cell body
D. schwann cells - surround the axon protecting it and providing insulation.
E. myelin sheath - forms a covering to the axon and is made up of membranes of the schwann cells
F. nodes of ranvier - constrictions between adjacent schwann cells

Question 116

describe an action potential? 1

Answer 116

• at rest, some potassium voltage-gated channels are open but the sodium voltage-gated channels are closed
• the energy of the stimulus causes some sodium voltage-gated channels in the axon membrane to open and so Na+ ions diffuse through these channels along the gradient
• as the Na+ ions diffuse, more sodium ion channels open, causing a greater influx of sodium ions by diffusion

Question 117

describe an action potential? 2

Answer 117

• once the action potential of +40mV has ben established, the voltage gates on the sodium ion channels close and the gates on the potassium channel begin to open
• with some potassium voltage-gated channels open, the gradient causes more potassium ion channels to open, this means that more K+ ions diffuse out starting repolarisation of the axon
• the outward diffusion of these K+ ions causes a overshoot of the gradient, with the inside of the axon being more negative. the gates on the potassium ion channels now close and cause Na+ ions to be pumped out and K+ ions in.

Question 118

what happens when Na+ ions are pumped out and K+ ions are pumped in?

Answer 118

the resting potential of -65mV is re-established and the axon is said to be repolarised

Question 119

how is resting potential set?

Answer 119

• Na+ ions are actively transported OUT of the axon by the sodium potassium pumps
• K+ ions are actively transported INTO the axon by the sodium potassium pump
• the active transport of Na+ ions is greater than that of K+ ions, so 3 Na+ ions move out for every 2 K+ ions that move in
• the outward movement of Na ion is greater than inward movement of K ions. as a result, more Na ions are surrounding the axon than the cytoplasm and more K ions are in the cytoplasm than the axon. therefore creating a gradient
• the Na ions diffuse back into the axon while the K ions diffuse back out of the axon

Question 120

describe the passage of an action potential along an unmyelinated axon?

Answer 120

1- at rest the conc of Na ion outside the axon membrane is higher than the inside, and the K ions conc is higher inside than outside. the overall conc is more positive on the outside. the axon membrane is polarised.
2- a stimulus causes an influx Na ions which is the action potential and the membrane is depolarised
3- behind the region of depolarisation, the sodium voltage gated channels close and the K ones open. K ions leave the axon along the gradient and depolarisation moves along the membrane
4- the outward movement of K ions has continued, to the point that the axon membrane behind the action potential has returned to its original state (positive outside, negative inside) its been repolarised
5- re-polarisation of the axon allows Na ions to be actively transported out, returning the axon to its resting potential

Question 121

what is the purpose of the refractory period?

Answer 121

1- it ensures that action potentials only move in one direction only
2- it produces discrete impulses, so they’re separated
3- limits the number of action potentials

Question 122

what are the similarities and differences between neuromuscular junction and a synpase?

Answer 122

• they both have neurotransmitters that are transported by diffusion
• they both use enzymes to break down the transmitter
• in a NMJ only motor neurones are used, in a cholinergic synapse all neurones are involved
• a NMJ is only excitatory and a cholinergic synapse may be excitatory or inhibitory

Question 123

what is tropomyosin?

Answer 123

it forms long thin threads that are wound around actin filaments.

Question 124

what is the homeostasis?

Answer 124

its the maintenance of a relatively constant internal environment. it ensures that cells of the body are in an environment that meets their requirements and allows them to function despite external changes

Question 125

how can temperature affect homestasis?

Answer 125

enzymes that control the biochemical reactions within cells, are sensitive to temperature. if it is too high, enzymes may denature as molecules vibrate too much, breaking the hydrogen bonds that holds their shape. the shape of the active site changes, so it no longer works as a catalyst, the metabolic rate is less efficient. the same applies for pH.

Question 126

how does blood concentration affect water potential?

Answer 126

• if its too high, the water potential of blood is reduced to a point where water molecules molecules diffuse out of cells into the blood by osmosis. this can cause cells to shrivel and die
• of its too low, cells are unable out normal activities as there isn’t enough glucose for respiration to provide energy

Question 127

what is a feedback mechanism?

Answer 127

by which a receptor responds to a stimulus created by the change to the system brought by the effector

Question 128

what is negative feedback?

Answer 128

occurs when a direction from an optimum causes changes that result in an even greater deviation from the normal

Question 129

what are endotherms? and exotherms?

Answer 129

• endotherms are organisms that derive most their heat from the metabolic activities which take place inside their bodies
• exotherms are organisms that obtain a proportion of their heat from sources outside their bodies eg the environment

Question 130

what does homeostasis involve?

Answer 130

multiple negative feedback systems, for each thing being controlled. this is because having more than one mechanism gives more control over changes in your internal environment than just having one negative feedback mechanism. having multiple negative feedback mechanisms means you can actively increase or decrease a level so it returns to normal

Question 131

what is positive feedback?

Answer 131

it occurs when the feedback causes the corrective measures to remain ‘turned on’. in doing so, it causes to deviate more from the original level

Question 132

where does blood glucose come from?

Answer 132

1. directly from the diet in the form of glucose absorbed following hydrolysis of other carbohydrates
2. from the hydrolysis in the small intestine of glycogen in glycogenolysis in the liver and muscle cells
3. from glucaneogenesis which is the production of glucose from sources other than carbohydrates

Question 133

what are the beta cells of islets langerhans?

Answer 133

they are small and produce the hormone insulin, found in the pancreas. they have receptors that detect the stimulus of a rise in blood glucose concentration and respond by secreting insulin directly into the blood plasma, which lowers the concentration.

Question 134

describe the process of secreting insulin to lower blood glucose level?

Answer 134

1. almost all cells have specific glycoproteins receptors on their cell surface membrane that bind specifically with insulin molecules.
2. insulin brings a change in the tertiary structure of the glucose transport carries proteins, causing them to change shape and open allowing more glucose into the cells by facilitated diffusion.
3. there is an increase in the number of the carrier proteins responsible for glucose transport in the cell surface membrane. at low concentrations, the protein from which these channels are made is part of the membrane of vesicles.
4. a rise in insulin concentration results in these vesicles fusing with the membrane so increasing the number of glucose transport channels
5. insulin then activates the enzymes that convert glucose to glycogen and fat

Question 135

what other ways is blood glucose concentration lowered?

Answer 135

by increasing;
1- the rate of absorption of glucose into the cells eg muscle
2- the respiratory rate of cells which use up glucose therefore increasing uptake of it in the blood
3- the rate of conversion of glucose into glycogen
4- the rate of conversion of glucose to fate

Question 136

what are alpha cells of the islets of langerhans?

Answer 136

they are larger cells and secrete glucagon. they detect a fall in blood glucose concentration by secreting the hormone glucagon directly into the blood plasma, where it raises blood glucose concentration.

Question 137

describe the process of secreting glucagon to lower blood glucose concentration?

Answer 137

1- glucagon attaches to a specific receptor proteins on the cell membrane of liver cells
2- it then activates enzymes to convert to glycogen to glucose in glycogenolysis
3- it activates enzymes involved in the conversion of amino acids into glucose in glucaneogenesis

Question 138

what happens at times of excitement and stress?

Answer 138

adrenaline is produced by the adrenal glands that lie above the kidneys. it raises the blood glucose concentration by attaching to protein receptors on the cell membrane of target cells and activating enzymes that causes the breakdown of glycogen to glucose in the liver

Question 139

how do insulin and glycogen act?

Answer 139

they antagonistically as they act in the opposite directions. the system is self regulation through negative feedback. however the concentration of blood glucose is not constant and fluctuates around the optimum point. only when the concentration falls below optimum point is insulin secretion reduced leading a rise in blood glucose/

Question 140

describe the second messenger model?

Answer 140

1- adrenaline binds to a trans membrane protein receptor within the cell surface membrane of a liver cell
2- the binding of the adrenaline causes the protein to change shape on the inside of the membrane
3- the change of protein shape leads to the activation of an enzyme called adenyl cyclase. the activated adenyl converts ATP to cyclic AMP (cAMP)
4- the cAMP acts as a second messenger that binds to protein kinase enzyme, changing its shape and therefore activating it
5- the active protein kinase enzyme catalyses the conversion of glycogen to glucose which moves out of the liver cell by facilitated diffusion and into the blood, through protein channels

Question 141

what is glycogenesis?

Answer 141

the conversion of glucose into glycogen. when blood glucose concentration is higher than normal the liver removes glucose from the blood and converts it to glycogen

Question 142

what is glycogenolysis?

Answer 142

the breakdown of glycogen to glucose. when blood glucose concentration is lower than normal, the liver can convert stored glycogen back into glucose which diffuses into the blood to restore the normal level

Question 143

what is gluconeogenesis?

Answer 143

the production of glucose from sources other than carbohydrates. when its supply of glycogen is exhausted, the liver can produce glucose from non-carbohydrate sources eg glycerol and amino acids

Question 144

what is diabetes?

Answer 144

its a metabolic disorder caused by an inability to control blood glucose concentration due to the lack of hormone insulin or a loss of responsiveness to it.

Question 145

what is type I of diaetes?

Answer 145

its due to the body being unable to produce insulin. it may be the result of an auntoimmune response where the body’s immune system attacks its own cells, eg the B cells of the islets of langerhans

Question 146

how can you control type 1 diabetes?

Answer 146

using injections of insulin. it cannot be taken by mouth, as its a protein so would be digested. the does must be matched to the glucose intake. to ensure the correct dose, blood glucose concentration is monitored by using biosensors. by injecting insulin and managing their diet and exercise they can lead normal lives

Question 147

what is type 2 diabetes?

Answer 147

its normally due to glycoprotein receptors on body cells being lost of losing their responsiveness to insulin, however it can also be because they have inadequate supply of insulin from the pancreas. it usually develops in people over 40, but there are cases arising in teenagers due to poor diet

Question 148

how can you control type 2 diabetes?

Answer 148

by regulating the intake of carbohydrates in the diet and matching this to their intake of exercise

Question 149

what is osmoregulation?

Answer 149

it is the homeostatic control of the water potential in the blood. in mammals, there are two kidneys found at the back of the abdominal cavity, one on each side of the spinal cord

Question 150

describe the structure of a kidney?

Answer 150

1. fibrous capsule - an outer membrane that protects the kidney
2. cortex - a region made up of renal (Bownman’s) capsule, convulated tubules and blood vessels
3. medulla - region made up of the loop of Henle, collecting ducts and vessels
4. renal pelvis - a funnel-shaped cavity that collects urine into the ureter
5. ureter - a tube that carries urine to the bladder
6. renal vein - returns blood to the heart via the vena cava
7. renal artery - supplies the kidney with blood from the heart via the aorta

Question 151

describe the first 3 features of a nephron?

Answer 151

1. renal (bownman’s) capsule - the closed end at the start of a nephron. it is surrounded by a mass of blood capillaries known as the glomerulus. the inner layer of the capsule is made from podocytes
2. proximal convulated tubule - a series of loops surrounded by blood capillaries. its walls are made of epithelial cells which have microvilli
3. loop of Henle - a loop that extends from the cortex into the medulla of the kidney and back again. its surrounded by blood capillaries

Question 152

describe the other two features of a nephron?

Answer 152

4. distal convulated tubules - a series of loops surrounded by capillaries. its walls are made of epithelial cells, but its surrounded by fewer capillaries than the proximal tubule
5. collecting duct - a tube into which a number of distal convulated tubules from a number of nephrons empty. it is lined by epithelial cells and becomes increasingly wide as it empties into the pelvis of kidney

Question 153

what are the afferent arteriole and glomerulus?

Answer 153

1. the afferent arteriole is a vessel that arises from the renal artery and supplies the nephron with blood. the arteriole enters the renal capsule of the nephron where it forms the glomerulus
2. glomerulus - a many branched knot of capillaries from which fluid is forced out of the blood. the glomerulur capillaries recombine to form the efferent arteriole

Question 154

what are the efferent arteriole and the blood capillaries?

Answer 154

3. efferent arteriole - a vessel that leaves the renal capsule. it has a smaller diameter than the afferent arteriole and so causes an increase in blood pressure within the glomerulus. it carries blood away from the renal capsule and branches to from the blood capillaries

Question 155

describe stage A - the formation of glomerulur filtrate by ultrafiltration?

Answer 155

1. blood enters the kidney through the renal artery, which branches to give tiny arteries each of which enters a renal (Bownman’s) capusle of a nephron. this arteriole is the afferent arteriole and divides to give the glomerulus
2. the glomerular cappilaries merges to form the efferent capsule. the walls of the glomerulur capillaries are made up of epithelial cells with pores between them. as the diameter of the afferent arteriole is greater than the efferent arteriole, there’s a build up of hydrostatic pressure within the glomerulus.
3. as a result, water, glucose and ions are squeezed out of the capillary to form the glomerulur filtrate. blood cells and proteins cannot pass into the renal capsule as they’re too large
4. the inner layer of the renal capsule is made up of cells called podocytes, which have spaces between them which allows filtrate to pass beneath them
5. as a result, the hydrostatic pressure in the blood in the glomerulus is sufficient to overcome the resistance and so filtrate passes from the blood into the renal capsule.

Question 156

what is the movement of the filtrate out of the glomerulus is resisted by?

Answer 156

• capillary epithelial cells
• connective tissue and epithelial cells of the capillary
• epithelial cells of the renal capsule
• the hydrostatic pressure of the fluid in the renal capsule space
• the low water potential of blood in the glomerulus

Question 157

describe stage B - the reabsorption of glucose and water by the proximal convulated tubule?

Answer 157

1. sodium are actively transported out of the cells lining the proximal convulated tubule PCT, into the blood capillaries which carry them away. the sodium ion concentration of these cells are lowered
2. the ions diffuse down a concentration gradient from the lumen of the PCT into the epithelial lining cells through special carrier proteins by facilitated diffusion
3. these proteins are specific and carry another molecule in co-transport
4. the molecules which have been co-transported into the cells of the PCT then diffuse into the blood. as a result, all the glucose, most other molecules and water are reabsorbed

Question 158

what are the adaptations of the PCT to reabsorb substances?

Answer 158

• microvilli to have a large SA to reabsorb substances from the filtrate
• infoldings at their bases to give a large SA to transfer reabsorbed substances into capillaries
• a high density of mitochondria to provide ATP for active transport

Question 159

describe stage C - maintenance of a gradient of sodium ions by the loop of Henle? 1

Answer 159

1. sodium ions are actively transported out of the ascending limb of the loop of Henle using ATP. this creates a low water potential between the ascending and descending limb, the interstitial region
2. the thick walls of the ascending limb are impermeable to water but the walls of the descending limb are permeable to water so it passes out of the filtrate by osmosis into the interstitial space
   3- the water potential gradually lowers throughout the descending limb as water leaves. at the base of the ascending limb, Na+ ions diffuse out of the filtrate and as it moves up the limb, these ions are actively pumped out which develops a higher water potential
3. the collecting duct is permeable to water and so filtrate moves down it, water passes out of it by osmosis into the blood vessels
4. as water passes out of the filtrate its water potential is lowered, however the water potential is also lowered in the interstitial space and so water moves out by osmosis down the whole length of the duct, a gradient is maintained

Question 160

describe stage D - the distal convulated tubule DST?

Answer 160

1. the cells that make up the walls of the DCT have microvilli and many mitochondria that allow them to reabsorb material from the filtrate, by active transport
2. the main role of distal tubule is to make adjustments to the water and salts that are reabsorbed and to control pH of the blood by selecting which ions to reabsorb.
3. to achieve this, the permeability of its walls become altered under the influence of hormones

Question 161

describe stage E - the counter current multiplier?

Answer 161

1. the filtrate in the ascending and descending limbs travel in opposite directions
2. the filtrate in the collecting duct has a lower water potential and meets the interstitial fluid that has even lower water potential, a gradient is maintained
3. the longer the loop the greater the reabsorption of water due to the more time to establish a gradient

Question 162

what are the first 4 stages of loss in water potential?

Answer 162

1. osmoreceptors in the hypothalamus of the brain detect a fall in the water potential and water leaves the receptors by osmosis
2. due to this water loss the osmoreceptors cells shrink, a change that causes the hypothalamus to release ADH
3. the ADH passes to the posterior pituiary gland where its secreted. ADH passes in the blood to the kidneys, where it increases the permeability to water of the cell surface membrane of cells that make up the DCT and the collecting duct
4. specific protein receptors on the membrane of these cells bind to ADH molecules, leading to an acitvation of the enzyme called phosphorylase

Question 163

whare the last 4 stages of loss in water potential?

Answer 163

5. the activation of the enzyme causes vesicles within the cell to fuse to the membrane. these vesicles contain pieces of plasma membrane that have aquaporins and so they fuse with the membrane and the number of water channels increases, making the membrane more permeable to water
6. ADH increases the permeability of collecting duct to urea which passes out, lowering the water potential of fluid around the duct. more water then leaves the duct by osmosis down a gradeint and re-enters the blood
7. as the reabsorbed water came from the blood initially the water potential stays the same, the osmoreceptors also send nerve impulses to the thirst centre to encourage the person to drink
8. the receptors detect a rise in water potential, and reduces the release of ADH and the permeability of the collecting ducts to water and urea reverts to its former state

Question 164

describe the process of decreasing the water potential?

Answer 164

1. the osmoreceptors detect the rise in the water potential and increase the frequency of nerve impulses to the pituitary gland to reduce its release of ADH
2. less ADH via the blood, leads to a decrease in the permeability of the collecting ducts and urea
3. less water is reabsorbed into the blood from the duct, more dilute urine is produced and the water potential of blood falls
4. when the water potential of the blood has returned to normal, the osmoreceptors in the hypothalamus cause the pituitary to raise its ADH release back to normal levels

Question 165

how does a fall in solute concentration of the blood raise the water potential?

Answer 165

• large volumes of water being consumed

- salts used in metabolism or excreted not being replaced in the diet

Question 166

differences between hormonal and nervous system?

Answer 166

• communication is by chemicals in hormonal, but by nerve impulses in nervous
• transmission is by blood in hormonal, but by neurones in nervous
• hormones travel to all parts of the body (only target cells respond) in hormonal, nerve impulses travel to specific parts of body in nervous
• response in hormonal is slow and long-lasting, in nervous its rapid and short lived
• effect may be permanent and irreversible in hormonal and effect in temporary and reversible in nervous

Question 167

how does an inhibitory synapse work?

Answer 167

1- presynaptic neurone releases neurotransmitter that binds to chloride ion protein channels on postsynaptic membrane
2- neurotransmitter causes Cl- channels to open
2- Cl- ions move into postsynaptic neurone by facilitated diffusion
4- binding of transmitter causes opening of nearby K+ protein channels
5- K+ ions move out of postsynaptic neurone into synapse
6- combined effect of Cl- ions moving in and K+ ions moving out is to make the inside of the postsynaptic membrane more negative and the outside more positive
7- membrane potential increases to -80mv compared to usual resting of -65mV
8- this is hyperpolarisation and makes it less likely that a new action potential will be created because larger influx of Na+ ions needed to produce one