action potential and neuromuscular transmission

Question 1

what are the two subdivisions of the autonomic nervous system

Answer 1

sympathetic/parasympathetic

Question 2

where are the axons and ganglia located in the PNS

Answer 2

outside the CNS lol

Question 3

what are the different components of a motor unit

Answer 3

anterior horn cell
motor nerve axon
all the nerve fibres it innervates

Question 4

in which order are motor units innervated when initiating movement

Answer 4

initate a few, then more motor units then more powerful ones

Question 5

how is the cell surface membrane selectively permeable

Answer 5

due to embedded proteins and water filled pores which function as signal receptors, ion channels, transport mechanisms, surveillance recognition monitors and enzymes

Question 6

what is the cell surface membrane impermeable to

Answer 6

water soluble compounds and ions

Question 7

what is resting potential in mV

Answer 7

-70 to -90 mV

Question 8

how is the membrane potential generated

Answer 8

• cell membrane is relatively permeable to K ions, K ions leak out therefore more negative inside cell
• impermeable to Na ions

Question 9

how can one work out what resting potential should be?

Answer 9

nernst equation

Question 10

ATPase pump, what ions move in and out

Answer 10

2K+ in
3Na+ out

Question 11

what is the nernst equation used for

Answer 11

the concentration ratio of an ion necessary to generate a particular potential difference

Question 12

how is the action potential initiated

Answer 12

during the conduction impulse - for about 1ms the membrane becomes more permeable to Na than to K.
so Na enters the membrane

Question 13

what is the threshold value and its role in the action potential

Answer 13

-55mV . this is when VgNa channels open so na+ flows down electrochemical gradient into cell membrane

Question 14

when being depolarised the cell membrane goes from __mV to __mV

Answer 14

-70mV to +30mV

Question 15

after being depolarised and being +30mV, what happens to the voltage gated channels (which open or shut) and what does this mean for the mV of the membrane

Answer 15

VgNa shut
VgK open = K flows out of cell and cell becomes repolarised

Question 16

what is the nature of the action potential once it starts. can it stop once it has started?

Answer 16

no, all or nothing response

Question 17

what is the refractory period

Answer 17

the period after an action potential before another one can be generated
due to the regenerative opening of VgNa channels

Question 18

is the action potential unidirectional or bidirectional and why

Answer 18

uni, bc refractory period

Question 19

how is nerve conduction velocity determined

Answer 19

• depends on rate at which membrane ahead can reach threshold
• depends on the longitudinal conductance of the cable
• which depends on cable diameter

Question 20

how are axons/nerves adapted to reduce loses, speed conduction and save energy

Answer 20

• insulated axons of large diameter
• schwann cells
• nodes of ranvier sodium, channels are clustered at each node
• saltatory conduction

Question 21

describe a synapse in detail starting from the arriving Ap

Answer 21

• the arriving AP triggers VgCa channels at the nerve terminal - open
• Ca enters the cell and triggers a cascade of reactions causing the membrane bound vesicles of AcCh to integrate with the presynaptic membrane
• AcCh molecules bind to (Nicotinic) acetylcholine receptors (ligand gated ion channel on the postsynaptic muscle membrane)
• various ions like Na rush in and depolarizes the muscle membrane
• a muscle action potential is propagated over the muscle cell membrane (sarcolemma) and down through the T Tubules to the inner aspects of the muscle fibre, in a similar fashion to a nerve action potential