Synapses and NMJs

Question 1

How do action potentials open Ca2+ channels?

Answer 1

Voltage gated Ca2+ channels open when the membrane depolarises.

Question 2

How are Ca2+ channels diverse?

Answer 2

Lots of different types but we will focus on L type seen in muscle neurones and the lungs because these are targeted lots on therapeutics.

Question 3

How does fast synaptic transmission occur?

Answer 3

Calcium eneters pre synaptic neurone.
Calscium binds synaptotagmin 
Vesicle (with neurotransmitter e.g. Ach) brought to membrane
Snare complex makes a fusion pore
Transmitter is released

Question 4

Outline the structure of a ligand gated ion channel.

Answer 4

Ligand binds and to receptor site intrinsic to ion channel causing a conformational chang that opens or closes the channel.

Question 5

Which NMJ is used in hunting?

Answer 5

Curare blocks NMJ

Question 6

What is myasthenia graves and why do patients get weakness?

Answer 6

Auto immune condition targetting nAChR. Antibodies target nAChR complement mediated lysis degrade the resetter. End plate potentials are thus low amplitude and muscle thus get weak and tired.

Question 7

List some properties of calcium channels.

Answer 7

Voltage gated calcium channels activate slower than VG-sodium channels.
Calcium channels can inactivate
Inactivation is dependent on calcium levels in the cell

Question 8

What destroys acetyl choline in NMJ?

Answer 8

acetylcholine esterase

Question 9

What happens if calcium availability at a NMJ is lowered?

Answer 9

Hypocalcaemia leads to less neurotransmitter release. Less ligand gated ion channels open on the muscle which causes less of a depolarisation. Threshold may not be met.

Question 10

What two types of NMJ blockers exist?

Answer 10

Competative blockers

Depolarising blockers

Question 11

Name a competative inhibitor at NMJs

Answer 11

Tubocurarine.

It binds the nicotinic receptor but does not form a conformational change so the ion channel remains shut and no sodium influxes.

Question 12

What does succinylcholine do?

Answer 12

Succinylcholine binds nicotinic receptors and keeps hem open meaning no local circuit and no propagation because adjacent sodium channels get inactivated.

Question 13

What nicotinic receptor is slow?

Answer 13

Muscarinic

Question 14

What is involved in mAChR?

Answer 14

GPCR and consequential cascade