6b (nervous coordination)

Question 1

what are nervous impulses?

Answer 1

chemical charges transmitted along a neurone
created by movement of sodium and potassium ions

Question 2

what is the resting potential membrane?

Answer 2

in a neurones resting state (not stimulated), outside of membrane is + compared to inside as there are more + charges outside

causes membrane to be polarised to there is a potential difference/ voltage (diff in charge) across it

Question 3

what is the voltage across a membrane at rest (resting potential)?

Answer 3

-70mV

Question 4

how is the resting potential created and maintained?

Answer 4

• sodium potassium pumps move sodium ions out of neurone but membrane isnt permeable to sodium ions so they cant diffuse back in
• creates a sodium ion electrochemical gradient because there are more + Na ions outside cell than in
• sodium potassium pumps also move potassium ions into the neurone
• when cells at rest, most potassium ion channels are open so the membrane is permeable to potassium ions so some diffuse back out through the channels
• even though + ions are moving in and out of cell, more move out than in so outside of cell is + charged compared to inside

Question 5

how do sodium potassium pumps maintain resting pot?

Answer 5

use active transport to move 3 sodium ions out of neurone for every 2 potassium ions moved in
ATP is required

Question 6

how do potassium ion channels maintain resting pot?

Answer 6

allow facilitated diffusion of potassium ions out of neurone, down conc grad

Question 7

what is action potential?

Answer 7

when a neurone is stimulated, sodium ion channels open
if stimulus big enough, triggers a rapid change in pot diff
causes cell membrane to depolarise

Question 8

describe graph of action potential

Answer 8

see poster or page 89

Question 9

what are the steps of action potential?

Answer 9

stimulus- excites cell membrane causing sodium ion channels to open. membrane more permeable to Na so Na+ ions so they diffuse into neurone down Na+ electrochemical gradient. inside of neurone becomes less -

depolarisation- if pot diff reaches threshold (55mV), more Na+ channels open so more Na+ diffuse into neurone

repolarisation- at around +30mV, Na+ channels close and K+ channels open so membrane more permeable to K so more K+ diffuse out of neurone down K+ conc grad. starts to get membrane back to resting pot

hyperpolarisation- K+ channels slow to close so slight overshoot where too many K+ ions diffuse out of neurone. pot diff becomes more - than resting pot (-70mV)

resting potential- ion channels are reset. sodium-potassium pump returns membrane to resting pot by pumping Na+ out and K+ in, maintains resting pot until membrane is excited by another stimulus

Question 10

what is the refractory period?

Answer 10

neurone cell membrane cant be excited again straight after action pot as ion channels are recovering and cant be made to open- Na+ channels closed during repolarisation and K+ channels closed during hyperpolarisation

acts as time delay between action potentials so they dont overlap. also limits frequency of nerve impulses, and ensures action pots are unidirectional

Question 11

what are waves of depolarisation?

Answer 11

when action pot happens, some Na+ ions that enter diffuse sideways
causes Na+ ion channels in next region to open and Na+ diffuse into that part
causes a wave of depolarisation which moves away from parts of membrane in refractory period as these parts cant fire an action pot

Question 12

what is the all-or-nothing principle

Answer 12

once threshold reached, action pot will always fire with same change in voltage no matter how big the stimulus is

if threshold isnt reached, action pot wont fire

bigger stimulus wont cause bigger action pot but will cause them to fire more frequently

Question 13

what 3 factors affect speed of conduction of action pots?

Answer 13

myelination
axon diameter
temperature

Question 14

how does myelination affect speed of conduction?
what saltatory conduction?

Answer 14

myelinated neurones have a myelin sheath which is an electrical insulator

in peripheral nervous system, sheath is made of schwann cells which have nodes of ranvier between them (bare membrane). sodium ion channels are concentrated at the nodes of ranvier

saltatory conduction
in myelinated neurones, depolarisation only happens at nodes of ranvier. neurones cytoplasm conducts enough electrical charge to depolarise next node so impulse jumps from node to node- this is very fast.
in non-myelinated neurones, impulse travels as a wave along whole length of axon membrane so you got depolarisation along whole length- slower

Question 15

how does axon diameter affect speed of conduction?

Answer 15

action pots conducted quicker along axons with bigger diameters as theres 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 16

how does temperature affect speed of conduction?

Answer 16

increases w temp as ions diffuse faster
speed only increases up to 40c then proteins begin to denature

Question 17

what is a synapse?
structure?

Answer 17

the junction between one neurone and another neurone or between a neurone and an effector eg muscle or gland cell

the gap between cells is the synaptic cleft

the presynaptic neurone has a swelling called the presynaptic knob which contains synaptic vesicles that are filled with neurotransmitters

Question 18

what is the effect of an action potential?

Answer 18

action pot reaches end of neurone, it causes neurotransmitters to be released into synaptic cleft

they diffuse across to postsynaptic membrane and bind to specific receptors

when neurotransmitters bind to receptors they might trigger an action pot, cause muscle contraction/ secretion of a hormone

neurotransmitters removed from cleft- hydrolysed by enzymes so broken down and products taken back to presynaptic neurone so responses don’t keep happening

Question 19

why are impulses unidirectional?

Answer 19

receptors are only on postsynaptic membranes
refractory period

Question 20

what is acetylcholine?

Answer 20

a type of neurotransmitter which binds to cholinergic receptors
synapses that use acetylcholine are called cholinergic synapses

Question 21

how is a nerve impulse transmitted across a cholinergic synapse?

Answer 21

1. action pot arrives at synaptic knob of presynaptic neurone. action pot stimulates voltage gated calcium ion channels in the presynaptic neurone to open. Ca2+ diffuse into synaptic knob (then pumped out afterwards by active transport)
2. influx of Ca2+ into synaptic knob causes synaptic vesicles to fuse w presynaptic membrane. vesicles release acetylcholine into synaptic cleft by exocytosis
3. ACh diffuses across synaptic cleft and binds to specific cholinergic receptors on postsynaptic membrane. causes sodium ion channels in postsynaptic neurone to open. influx of sodium ions into postsynaptic membrane causes depolarisation. action pot on postsynaptic membrane is generated if the threshold is reached. ACh is removed from synaptic cleft so response doesnt keep happening. its broken down by acetylcholinase and products are re-absorbed by presynaptic neurone and used to make more ACh

Question 22

what are excitatory neurotransmitters?
example

Answer 22

neurotransmitters that depolarise the postsynaptic membrane making it fire an action potential if the threshold is reached
eg acetyl choline at cholinergic synapses in CNS and at neuromuscular junctions

Question 23

what are inhibitory neurotransmitters?
example

Answer 23

neurotransmitters that hyperpolarise the postsynaptic membrane (make pot diff more negative), preventing it from firing an action pot
eg GABA and acetylcholine at cholinergic synapses in the heart

Question 24

what is an inhibitory synapse?

Answer 24

a synapse where inhibitory neurotransmitters are released from the presynaptic membrane following an action potential

Question 25

what is summation?

Answer 25

where the effect of neurotransmitters released from many neurones (one one thats stimulated lots in short period of time is added together it means synapses accurately process information, finely tuning the response.

Question 26

what are the 2 types of summation?

Answer 26

spatial summation and temporal summation

Question 27

what is spatial summation?

Answer 27

where 2 or more presynaptic neurones release their neurotransmitters at the same time onto the same postsynaptic neurone small amount of neurotransmitter released from each of these neurones can be enough altogether to reach the threshold in the postsynaptic neurone and trigger an action pot if some neurones release an inhibitory neurotransmitter, then total effect of all neurotransmitters might be no action potential

Question 28

what is temporal summation?

Answer 28

where 2 or more nerve impulses arrive in quick succession from the presynaptic neurone. makes action pot more likely to fire as more neurotransmitter is released into synaptic cleft

Question 29

what is a neuromuscular junction?

Answer 29

specialised cholinergic synapse between motor neurone and muscle cell use the neurotransmitter acetylcholine which binds to cholinergic receptors called nicotinic cholinergic receptors

Question 30

what is acetylcholinesterase?

Answer 30

enzyme that breaks down ACh in the synaptic cleft

Question 31

differences between neuromuscular junctions and cholinergic synapses

Answer 31

at neuromuscular junctions: - postsynaptic membrane has lots of folds that form clefts which store AChE - postsynaptic membrane has more receptors than other synapses - ACh is always excitatory, so when neurone fires action pot, it normally triggers a response in a muscle cell

Question 32

what are agonist drugs? eg

Answer 32

drugs that are the same shape as the neurotransmitters so mimic their action at receptors. results in more receptors being activated eg nicotine mimics acetylcholine so binds to nicotinic cholinergic receptors in the brain

Question 33

what are antagonistic drugs? eg

Answer 33

drugs that block receptors so they cant be activated by neurotransmitters results in fewer (if any) receptors being activated eg curare blocks effects of acetylcholine by blocking nicotinic cholinergic receptors at neuromuscular junctions so muscle cells cant be stimulated.

Question 34

what do drugs other than agonistic and antagonistic drugs do?

Answer 34

some inhibit enzymes that break down neurotransmitters so there are more neurotransmitters in the synaptic cleft to bind to receptors and theyre there for longer some stimulate release of neurotransmitters from presynaptic neurone so more receptors are activated some inhibit release of neurotransmitters from the presynaptic neurone so fewer receptors are activated

Question 35

what are the 3 types of muscle?

Answer 35

smooth muscle- contracts wo conscious control. found in walls of internal organs apart from heart cardiac muscle- contracts wo conscious control but is only found in heart skeletal muscle- type of muscle used to move eg biceps and triceps

Question 36

what are tendons and ligaments?

Answer 36

tendon- attach muscles to bones ligaments- attach bones to bones

Question 37

what are antagonistic pairs?

Answer 37

muscles that work together to move a bone contracting muscle is agonist and relaxing is antagonist need antagonistic pairs as muscles can only pull, cant push

Question 38

describe the structure of skeletal muscle

Answer 38

made of bundles of muscle fibres. the cell membrane of muscles fibres is called sarcolemma. bits of sarcolemma fold inwards across muscle fibres and stick into sarcoplasm (muscle cytoplasm) these folds are transverse tubules and they help to spread electrical impulses throughout sarcoplasm so reach all parts of muscle fibre sarcoplasmic reticulum run through the sarcoplasm. this stores and releases calcium ions that are needed for muscle contraction. muscle fibres have lots of mitochondria to provide ATP for contraction. they are multinucleate (many nuclei), have lots of myofibrils which are made up of proteins and are highly specialised for contraction

Question 39

what are myofibrils?

Answer 39

contain bundles of thick and thin myofilaments that move past each other to make muscles contract. thick myofilaments are made of protein myosin thin myofilaments made of protein actin myofibrils have dark bands- myosin and some overlapping actin, and light bands- actin only myofibrils are made of sarcomeres which have an m line and a h zone

Question 40

what are A bands?

Answer 40

the dArk bands in myofibrils that contain myosin and some overlapping actin only one that stays the sAme length

Question 41

what is the Z line?

Answer 41

the end of a sarcomere

Question 42

what is the M line?

Answer 42

the middle of each sarcomere- the middle of the myosin filaments

Question 43

what is the H zone?

Answer 43

around the M line only contains myosin filaments

Question 44

what are I bands?

Answer 44

the lIght bands in myofibrils that contain only actin

Question 45

what is the sliding filament theory?

Answer 45

- bulbous heads of myosin form cross-bridges with actin by attaching to binding sites on actin and flexing in unison, pulling actin filaments along myosin filaments - they become detached using ATP as a source of energy to return to original angle and reattach further along filaments - repeated 100x/s

Question 46

evidence for sliding filament theory

Answer 46

myofibrils appear darker where actin and myosin overlap appear lighter where they dont overlap there should be more overlap in contracted muscle if theory correct

Question 47

myosin filaments

Answer 47

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

Question 48

actin filaments

Answer 48

have binding sites for myosin heads called actin-myosin binding sites tropomyosin is found between actin filaments- helps myofilaments move past each other

Question 49

describe the sliding filament theory

Answer 49

1. action pot reaches muscle and response is stimulated 2. Ca2+ enter and cause tropomyosin to move and uncover binding sites 3. whilst ADP attached to myosin head, it can bind to binding site on actin to form cross bridge 4. angle created in cross bridge creates tension so actin filament is pulled and slides along myosin- ADP released 5. ATP can then bind to myosin head causing shape change so detaches from actin 6. ATPase in sarcoplasm is activated by Ca2+ to hydrolyse ATP on myosin head into ADP and release enough energy for myosin head to return to og position 7. process repeats whilst Ca2+ remains high (whilst muscle remain stimulated)

Question 50

what happens when a muscle returns to resting state?

Answer 50

Ca2+ leave binding sites and are actively transported back into sarcoplasmic reticulum causes tropomyosin to return, so block anti-myosin binding sites. muscles arent contracted because no myosin heads are attached to actin filaments (so no actin-myosin cross bridges). actin filaments slide back to relaxed position, which lengthens sarcomere

Question 51

what is energy used for in muscle contraction

Answer 51

energy needed for the return movement of myosin heads that causes actin filaments to slide the return of Ca2+ back into sarcoplasmic reticulum occurs via active transport

Question 52

how is ATP generated so exercise can continue (3 ways)

Answer 52

1. aerobic respiration most ATP generated through oxidative phosphorylation in mitochondria. aerobic resp only works when theres oxygen so its good for long periods of low intensity research 2. anaerobic respiration ATP is made rapidly by glycolysis. end product of glycolysis is pyruvate which is converted to lactate fermentation. lactate can quickly build up in muscles and cause muscle fatigue. anaerobic resp is good for short periods of hard exercise 3. ATP-phosphocreatine ATP made by phosphorylating ADP- adding phosphate group taken from PCr. (ADP +PCr -> ATP + Cr) PCr is stored inside cells and ATP-PCr system generates ATP very quickly. PCr runs out after few secs so is used during short bursts of vigorous exercise. ATP-PCr system is anaerobic and alactic (doesnt form lactate) some creatine gets broken down into creatinine which is removed from body via kidneys. creatinine levels higher in people who exercise reg and have high muscle mass. high creatinine levels may indicate kidney damage

Question 53

what are slow twitch muscle fibres?

Answer 53

contract slowly and work for long period of time wo getting tired good for endurance activities high proportions in back and calf muscles as they maintain posture energy released slowly through aerobic resp. lots of mitochondria and blood vessels to supply muscle w oxygen. mitochondria found mainly near edge of muscle fibres so short diffusion pathway for oxygen rich in myoglobin (red-coloured protein that stores oxygen, so red colour)

Question 54

what are fast twitch muscle fibres?

Answer 54

contract very quickly but also get tired quickly so good for short bursts of speed and power. high proportions found in muscles used for fast movement eg arms, legs, eyes energy released through anaerobic resp using glycogen. also have stores of PCr so energy can be generated very quickly when needed few mitochondria and blood vessels. not much myoglobin either, so cant store much oxygen, so white colour

Question 55

how are slow twitch muscle fibres adapted?

Answer 55

large store of myoglobin- stores oxygen rich supply of blood vessels- deliver oxygen and glucose for aerobic resp numerous mitochondria- produce ATP

Question 56

how are fast twitch muscle fibres adapted?

Answer 56

thicker, more numerous filaments high conc of glycogen high conc of enzymes involved in anaerobic resp- provide ATP rapidly store of phosphocreatine- rapidly generate ATP from ADP in aerobic conditions so provide energy for muscle contraction

Question 57

what is tropomyosin?

Answer 57

forms long thin threads that are wound around actin filaments

Question 58

compare and contrast neuromuscular junctions and cholinergic synapses

Answer 58

neuromuscular junctions: - unidirectional - only excitatory - connects motor neurone to muscles - end point for action pot - acetylcholine binds to receptors on muscle fibre membranes cholinergic synapses: - unidirectional - excitatory or inhibitory - connect 2 neurones - new action pot generated in next neurone - acetylcholine binds to receptors on post-synaptic membrane of a neurone