6. neuromuscular junction

Question 1

NMJ

Answer 1

specialised synapse between neurones and muscle

• single axon single fibre FINE control (eye)
• single axon multiple fibres LARGE control (biceps)

Question 2

How does an AP in motor neurone lead to contraction of muscle fibre?

Answer 2

1. AP in motor neurone arrives at axon terminal
2. terminal membrane depolarises, vg calcium channels open
3. calcium enters via ec gradient
4. calcium mediated exocytosis of Ach
5. Ach binds to nicotinic Ach receptor- conformational change- Na influx K efflux- generating a receptor potential (mEPP)
6. if RGP passes threshold- AP generated
7. AP propagates through muscle, release of calcium ions from SR- contraction of muscle

Question 3

quantal exocytosis

Answer 3

small quanta of Ach released randomly at rest

release from single synaptic vesicle- small membrane depolarisation- mEPP -0.4mV in amplitude

Question 4

interaction of Ach and nAchR

Answer 4

stimulus secreting coupling
lots of nAChR compared to Ach
increases capacity of Ach detection

Question 5

Ach esterase

Answer 5

released Ach inactivated via enzyme hydrolysis in synaptic cleft

Ach-> acetate +choline (AchE)-> recycled in pre synaptic bouton

Question 6

Myasthenia Gravis

Answer 6

auto antibodies against nAChR

autoimmune disorder of neuromuscular transmission

Question 7

MG symptoms etc

Answer 7

more common in women
muscle weakness, cannot prolong contraction
ptosis (droopy eyelid)
progressive symptoms

Question 8

MG treatment

Answer 8

anti-cholinesterase as first line to increase conc of Ach

Question 9

skeletal muscle cell has

Answer 9

one cell has one NMJ

one-one synapse (one presynaptic AP-> one postsynaptic AP)