Somatic Nervous System

Question 1

overview of somatic NS

Answer 1

single motor neurone connecting CNS to skeletal muscle

cell bodies = in brain stem

Question 2

motor unit

Answer 2

motor neuron + muscle fibres

Question 3

neuromuscular junction

Answer 3

synaptic connection between terminal end of motor nerve + muscle

Question 4

what happens after an action potential is conducted along the motor nerve?

Answer 4

depolarisation

=> influx of Ca2+ at nerve terminal

ACh released from storage vesicles in synapse

then metabolised by acetylcholine esterase

Question 5

nicotinic receptors on skeletal muscle endplate

Answer 5

ligand-gated ion channel

contains alpha, beta, delta + gamma subunits

2 Ach binding sites

Question 6

ions involved at the skeletal muscle endplate

Answer 6

Na+ in

K+ out

Question 7

what happens once ACh has bound to the nicotinic receptors on the motor end plate?

Answer 7

Na+ influx = end-plate potential generation

initiates opening of proximal voltage-gated Na+ channels

AP generated in muscle cell = opening of L-type calcium channels
=> stimulates Ca2+ release from stores

Question 8

3 ways drugs may interfere with cholinergic transmission at NMJ

Answer 8

block nicotinic cholinergic receptors

decrease ACh at NMJ (inhibit ACh synthesis or release)

increase ACh at NMJ (enhance nicotinic effect)

Question 9

non-depolarising agents

Answer 9

nACH receptor ANTAGONISTS

Question 10

depolarising-blocking agents

Answer 10

weak nicotinic AGONISTS

structurally similar to ACh (both quaternary ammonium compounds)

Question 11

how do non-depolarising agents work?

Answer 11

block neuromuscular transmission

COMPETES with ACh for receptors

Question 12

how do depolarising agents work?

Answer 12

cause prolonged stimulation/densitisation of receptors

mimics ACh and bind to nicotinic receptors
-> opens end plate voltage sensitive Na+ channels
-> prolonged depolarisation of muscle