Neurotransmitter Release

Question 1

What happens in the axon terminal once the NT is released?

Answer 1

The vesicle is released and ATP is used to pump Ca2+ back out again

Question 2

What type of Ca2+ channels are used in NT release?

Answer 2

L-type, voltage gated

Question 3

Describe what happens when ACh binds to a nAChR

Answer 3

ACh binds to alpha sub unit, confirmational change allows transport of Na+ in, K+ out, this depolarises the membrane producing an action potential

Question 4

What part of a nicotinic ACh receptor does ACh bind to?

Answer 4

Alpha sub unit

Question 5

Where are nAChR found?

Answer 5

Skeletal muscle, CNS (post-ganglionic) PNS

Question 6

Steps in NT release?

Answer 6

AP arrives, causing depolarisation, depolarisation opens V. Gated Ca2+ channels (VOCC), Influx of Ca2+, Ca2+ binds to Synaptotagmin, this brings vesicle to the pre-synaptic membrane. Proteins arrange and form a SNARE complex which forms a pore, allows vesicle to dock and fuse allowing contents to leave.

Question 7

If ACh binds to an M3 muscarinic receptor, what G protein sub unit would dissociate? And what would this act upon?

Answer 7

Alpha q acts upon Phospholipase C

Question 8

If ACh binds to an M2 muscarinic receptor, what sub unit would dissociate and what would this act upon?

Answer 8

Alpha i would act upon Adenylyl cyclase, inhibiting it’s activity.

Question 9

What other effect do M2 receptors have when stimulated by parasympathetic NS?

Answer 9

Causes opening of muscarinic K+ channels, causing efflux of K+, hyperpolarising the membrane, making it more -ve (eg allowing HR to decrease)

Question 10

What are the two types of nicotinic blockers?

Answer 10

Competitive blockers and Depolarising blockers

Question 11

Give an example of a competitive and depolarising blocker

Answer 11

Competitive= tubocararine. Depolarising= succinylcholine.

Question 12

What does a competitive nicotinic blocker do?

Answer 12

Binds at ACh binding site, TF ACh cant bind. (This isnt permanent, doesnt trigger conformational change) It is possible to outcompete with increased [ACh]

Question 13

Effect of nicotinic competitive blocker?

Answer 13

Would paralyse muscle, TF used as an anaesthetic

Question 14

What does a nicotinic depolarising blocker do?

Answer 14

Act as an ACh agonist, but as they are not broken down by AChesterase, they will remain bound. TF will remain depolarised TF Na+ channels will become and remain inactivated.

Question 15

What is a depolarising blocker used for? (Give name)

Answer 15

Succinylcholine. Short term paralysis/relaxation of muscles.