Nervous Co Ordination

Question 1

How is resting potential established? (6 marks)

Answer 1

1) Na+ actively transported out of axon membrane through Na+/K+ pump
2) K+ actively transported into axon membrane through Na+/K+ pump
3) greater active transport of Na+ as three Na+ moved out of axon membrane for ever 2K+ that move inside.
4) Electrochemical gradient created in axon membrane so more Na+ in tissue fluid outside axon than in axoplasm where there is a higher concentration of K+.
5) Na+ begin to diffuse back into axon whilst K+ diffuses out through their respective leak protein channels.
6) most K+ voltage gated channels are open, whilst ALL Na+ voltage gated channels are closed, therefore more negatively charged inside axon membrane and more positively charged outside, which generates membrane resting potential of -65mV, where membrane is polarised. Pump maintains and restores this conc gradient

Question 2

Purpose of Na+/K+ pump in resting potential?

Answer 2

Maintains and restores concentration gradient across axon membrane

Question 3

Describe and explain the three factors that affect speed of action potentials.

Answer 3

Myelin sheath - acts as an electrical insulator as there are no Na+ or K+ gates in this part of axon, creating a longer electrical circuit, hence saltatory conductions occur as depolarisation only occurs at nodes of ranvier which increases speed.

Diameter of axon - greater diameter, means less leakage of ions so faster speed of action potential

Temperature - affects rate of diffusion of ions, hence affects speed of impulses and therefore the speed and strength of muscle contractions - higher temperatures mean faster till denaturisation of proteins, the cells no conduction

Question 4

Ectotherms and relation to action potentials

Answer 4

Environment temperature = their body temperature and hence affects speed and strength of muscle contractions

Question 5

Why people with MS often have slow reaction times

Answer 5

Lack of myelinated sheaths

More time needed for depolarisation across a longer area of axon membrane due to lack of saltatory conduction

Question 6

How does saltatory conduction work?

Answer 6

Myelin sheaths have a lack of Na+/K+ gates so depolarisation only occurs at the nodes of ranvier
Hence longer electrical circuit present and action potential jumps from one node to another

Question 7

Describe and explain how action potential occurs. (8 points)

Answer 7

1) impulse passed between nodes of ranvier
2) At resting potential of -70mv Only K+ leak protein channels open and more K+ channel proteins than Na+ so membrane is more permeable to K+. Na+/K+ pump actively transports 3 Na+ out of axon membrane for every 2 K+ in. Hence maintains and restores concentration gradient with inside axon membrane being more negatively charged.
3) Stimuli causes some Na+ voltage gated channels to open, hence some influx of Na + into axon membrane.
4) if stimulus is not large enough, threshold is not reached, and no action potential is generated (all or nothing principle). If stimulus is large enough and threshold of -55mv is reached, then all Na + voltage gated channels open and influx of Na+ into axon membrane via FD, so depolarisation occurs and +40 mv of action potential is reached.
5) All Na+ voltage gated channels close at +40mv and all K+ voltage gated channels open
6) efflux of K+ out of axon via fd
7) hyperpolarisation occurs and K+ voltage gated channels close when -80mv/-90mv is reached
8) refractory period is over. Na+/K+ now becomes active and restores and maintains concentration gradient so resting potential of -70mv is again reached. Now that refractory period is over another action potential can occur.

Question 8

How is action potential generated (1 mark answer)

Answer 8

Sudden momentary increase in permeability of the axon membrane

Question 9

Define refractory period

Answer 9

No Inward movement of Na+ into axon because Na+ bolted gated channels are closed

Question 10

3 purposes of the refractory period

Answer 10

• ensures action potentials are propagated in one direction only as action potentials can only be passed from active to resting regions; not in a region in the refractory period so action potential does not spread in both directions.
• produces discrete impulses, due to refractory period action potential can not be formed immediately after first one so ensures action potentials are separate
• limits the number of action potentials… because action potentials are separate it limits the number of action potentials that can be passed along an axon in a given time so limits the strength of stimulus that can be detected

Question 11

Very strong stimulus wave graph

Answer 11

Large amplitude

Quick frequency

Question 12

Neurotransmitters that are excitatory and hence related to which ion?

Answer 12

Noradrenaline
Dopamine
Ca2+

Question 13

Neurotransmitters that are inhibitory and hence related to which ion?

Answer 13

Serotonin
GABA
Cl-

Question 14

Nicotine and ach

Answer 14

Similar shape so binds to ach receptors
Produces similar effects
Lasts longer because acetylchloinesterase can not release it from receptor,

Question 15

Botulinum toxin and ach

Answer 15

Prevents release of Ach
So no depolarisation of post synaptic neurone
Paralysis occurs

Question 16

Synapses structure

Answer 16

Axon
Pre synaptic knob
Synaptic cleft
Post synaptic

Question 17

Function of synapses

Answer 17

A large stimulus creates a number of simultaneous responses because a single impulse along one neurone can initiate new impulses in several neurones

A number of impulses can be combined at a synapse to allow nerve impulses from different receptors reacting to different stimuli to create a single response

Question 18

State and explain two features of synapses

Answer 18

Unidirectional: synapses can only pass information in one direction; from pre synaptic to post synaptic

Summation: low frequency of action potential lead to release of insufficient neurotransmitter to trigger action in post synaptic neurone - hence summation leads to the buikd up of neurotransmitter in post synaptic cleft

Question 19

Spatial summation

Answer 19

Many different pre synaptic neurones release enough neurotransmitter to exceed threshold of post synaptic neurone to trigger an action potential - (many pre at once)

Question 20

Temporal summation

Answer 20

Single pre synaptic neurone releases neurotransmitter many times over a short period - once enough build up exceeds threshold then a new action potential is triggered.

One pre many times quickly

Question 21

Describe and explain cholinergic synapse (excitatory)

Answer 21

1) an action potential arrives and initiates synaptic transmission
2) Na+ voltage gated channels open, depolarising axon membrane, due influx of Na+
3) depolarisation of terminal membrane cause Ca2+ voltage gated channels to open
4) influx of Ca2+ unit cell triggers fusion of acetylcholine vesicles with pre-synaptic membrane
5) Acetylcholine molecules diffuse across synaptic cleft and bind to protein recoetors on post synaptic membrane
6) binding triggers opening of chemically gated Na+ protein channels. Influx of Na+ into postsynaptic membrane trigger depolarisation
7) spreading depolarisation in postsynaptic membrane fires an action potential in adjacent membrane
8) Acetylcholinesterase enzyme hydrolyses acetylcholine from receptors on postsynaptic membrane into ethanoic acid and choline acid, which is taken back up by presynaptic neurone for resynthesis which prevents continuous firing of action potentials
9) After synaptic transmission acetylcholine and vesicles are recycled

Question 22

How is continuous firing of post synaptic membrane stopped

Answer 22

Acetylcholinesterase breaks down ach bound to recpetors

Question 23

Describe and explain process in inhibitory synapses

Answer 23

Pre synaptic neurone releases a neurotransmitter that binds to Cl- protein channels on post synaptic neurone
Neurotransmitter binding causes conformational change to Cl - protein channels so Cl- protein channels to open
Cl- moves via fd into post synaptic neurone
Binding of neurotransmitter also causes nearby K+ protein channels to open
K+ moves out of post synaptic neurone into synapse via fd
Combined effect of influx of Cl- and effort of K+ makes inside axon more negative and the outside more positive
Hence membrane is hyperpolarised to as much as -80mv which makes it less likely a new action potential will be created therefore a larger influx of Na+ needed to meet threshold so inhibits new action potentials.

Question 24

Slow twitch is what type and fast twitch is what type

Answer 24

1

2

Question 25

Slow twitch

Answer 25

Stamina 
Aerobic 
Endurance 
Rich blood supply 
Large amount of energy released slowly 
Many mitochondria 
A lot of myoglobin

Question 26

Fast twitch

Answer 26

Strength 
Sprinters 
Anaerobic 
Poor blood supply 
Small amount of energy released quickly 
Very little mitochondria 
Very little myoglobin

Question 27

Neuromuscular junctions

Answer 27

Motor neurone meets skeletal muscle fibre

Many junctions along muscle

Question 28

If only one neuromuscular junctions then what would happen?

Answer 28

Take time for wave of contraction to travel across the muscles, hence not all fibres contract simultaneously hence slow movement - for survival rapid co-ordinated contraction of muscles needed.

Question 29

Neuromuscular junction vs cholinergic synapse

Answer 29

Excitatory vs excitatory or inhibitory
Only neurone to muscle vs neurone to other neurone/effectors
Only motor neurones involved/ motor sensory and intermediate
Action potential ends here vs new action potential may be produced
Acetylcholine binds to receptors on muscle fibre vs binds to receptors on post-synaptic membrane