nerves and muscles

Question 1

describe the sliding filament model

Answer 1

1. Ap spreads down T tubules and Calcium released from sarcoplasmic reticulum and travels down sarcoplasm to myofibrils
2. calcium ions binds to tropomyosin and changes shape and exposes myosin binding site on actin
3. Myosin heads (ADP attached) bind to binding sites which requires ATP
4. power stroke- myosin head ‘cocks’ sliding actin along myosin (ADP released)
5. ATP causes myosin to detach from actin binding site which breaks cross bridge
6. Hydrolysis of ATP provides energy for myosin to return to its original position (recovery stroke)
7. Myosin head attaches to different binding site further along actin filament

Question 2

how does myelination affect speed of conduction

Answer 2

depolarisation at nodes of ranvier only (saltatory conductance)
AP doesn’t travel down whole axon so there’s no need to depolarise whole axon unlike unmyelinated neurone

Question 3

how does axon diameter effect speed of diameter

Answer 3

bigger diameter= less leakage of ions

Question 4

how does temperature affect speed of conductance

Answer 4

more kinetic energy= increased movement of sodium and potassium ions
which increases rate of respiration which increases ATP therefore AT faster

Question 5

what is the refractory period

Answer 5

time taken to restore axon to resting potential

Question 6

what is the importance of the refractory period

Answer 6

1. discrete and discontinuous impulses (action potentials don’t over lap)
2. limits frequency of impulse transmission at a certain intensity
3. unidirectional action potential

Question 7

what is summation

Answer 7

addition of number of impulses covering a post synaptic neurone

Question 8

what is temporal summation

Answer 8

one pre synaptic neurone produces many impulses over short period

Question 9

what is spatial summation

Answer 9

many pre synaptic neurone share same post synaptic neurone

Question 10

describe a myelinated neurone

Answer 10

depolarisation on nodes of ranvier only, saltatory conduction, whole axon doesn’t need to be depolarised

Question 11

describe a non myelinated neurone

Answer 11

AP passes as a wave of depolarisation and there is influx of sodium ions in 1 region which increases permeability to sodium ions in adjoining region therefore influx of sodium ions and therefore adjoining region depolarised

Question 12

how is a resting potential established

Answer 12

1. sodium/ potassium ion pump
   - 3 NA+ out of axon
   -2K+ in axon
2. creates electrochemical gradient
   - more sodium ions out of axon and more potassium ions inside axon
3. membrane more permeable to potassium ions therefore K+ channels open
4. therefore K+ leaves axon
5. inside axon relatively negative to outside therefore polarised= resting potential

Question 13

transmission across cholinergic synapse

Answer 13

1. AP arrives causing Ca2+ channels to open
2. influx of Ca2+ causes vesicles to move and fuse with presynaptic membrane
3. neurotransmitter released into synaptic cleft and diffuse across synaptic cleft
4. NT bind to specific receptors on post synaptic membrane
5. causes Na+ channels to open
6. influx of Na+ into post synaptic knob causes depolarisation and induces action potential
7. neurotransmitter removed from synaptic cleft

Question 14

all or nothing principle

Answer 14

1. stimulus- membrane more permeable to sodium ions so sodium channels open and sodium diffuses into neurone
2. depolarisation -pd reaches threshold and action potential generated because more sodium channels open and sodium ions diffuse more rapidly
3. repolarisation- Na+ channels close and K+ channels open so K+ diffuse out of neurone
4. hyperpolarisation- K+ channels slow to close and slight overshoot
5. resting potential restored through sodium potassium pump

Question 15

role of phosphocreatine

Answer 15

Per stored in cells
rapidly produces ATP by phosphorylating ADP