ICPP 5 Neuromuscular Junction

Question 1

What is the neuromuscular junction?

Answer 1

Synapse between a nerve and skeletal muscle fibre

Question 2

What happens at the nerve terminal of the neuromuscular junction?

Answer 2

1- AP
2- VGCC open
3- Ca2+ entry
4- Ca2+ binds to synaptotagmin
5- vesicle brought close to membrane
6- snare complex makes fusion pore
7- neurotransmitter releases through pore

Question 3

How do you increase the amount of neurotransmitter released?

Answer 3

Increased frequency of AP

Question 4

Compare and contrast the response time between muscarinic and nicotinic acetylcholine receptors

Answer 4

• nAChR - faster > ligand gated ion channel
• mAChR - slower > GPCR > triggers cascade of intracellular events

Question 5

What are the mechanisms of neuromuscular blockers?
Examples

Answer 5

• competitive blocker e.g. tubocurarine
• depolarising blocker e.g. succinylcholine

Question 6

What is the action of tubocurarine?
Can it be overcome, if yes how?

Answer 6

Competitive blocker for neuromuscular junction

Yes - increasing ACh conc.

Question 7

What is the action of succinylcholine?

Answer 7

Maintained depolarisation
VGNC become inactivated

Question 8

What is myasthenia gravies?

Answer 8

Autoimmune disease
Targets ACh receptors

Question 9

Explain why myasthenia gravies causes weakness

Answer 9

• autoantibodies directed against nAChR
• causes cell lysis + receptor degradation
• endplate potentials are reduced in amplitude
• leads to muscle weakness + fatigue

Question 10

What is an illness related to the neuromuscular junction?

Answer 10

Myasthenia gravis

Question 11

What test is used to confirm myasthenia gravis?

Answer 11

Edrophonium test