ICPP 5

Question 1

What determines whether an action potential is generated in an axon hillock?

Answer 1

Whether summation of EPSP and IPSP reaches threshold potential.

Question 2

What happens to the membrane potential of an ion if the conductance is increased?

Answer 2

The membrane potential will move closer to the equilibrium potential.

Question 3

What happens during the upstroke of an action potential?

Answer 3

Na+ channels open and Na influx depolarises cell to threshold level which causes more Na+ channels to open…

Question 4

What happens during the downstroke of an action potential?

Answer 4

Na+ channels close and become inactivated.

K+ channels open, K+ efflux returns membrane potential to resting.

Question 5

What is hyperpolarisation?

Answer 5

When the membrane potential is lower than resting level due to more K+ channels being open.

Question 6

What causes hyperpolarisation?

Answer 6

Slow closing of the K+ channels

Question 7

How do sodium channels become re-activated?

Answer 7

Inactivation pore inactivates them, this is only removed when the membrane becomes hyperpolarised and the channel then closes.

Question 8

What is the absolute refractory period?

Answer 8

When the sodium channels are all inactivated. No matter how strong a stimulus, an AP cannot be generated.

Question 9

How is the relative refractory period different to the absolute refractory period?

Answer 9

In RRP, Na+ channels are recovering from inactivation, so if a stimulus is large enough then an AP may be generated.

Question 10

How many polypeptides are there in 1 functional Na+ channel?

Answer 10

1

Question 11

Outline the structure of a voltage gated Na+ channel.

Answer 11

1 polypeptide with 4 domains.
Each domain has voltage sensor in transmembrane spanning region 4.
Between the 3rd and 4th domain there is an inactivation particle.
There is a p region which dictates which ion channel flows through.

Question 12

How do voltage gated K+ channels differ?

Answer 12

4 polypeptides make up 1 functional channel.

No inactivation particle.

Question 13

What is the mechanism of action of local anaesthetics?

Answer 13

They block Na+ channels, stopping action potential generation in pain fibres.

Question 14

What order do local anaesthetics block axons?

Answer 14

1. Small myelinated
2. unmyelinated
3. Large myelinated

Question 15

Local anaesthetics work in a use-dependent manner, explain this.

Answer 15

They block the ion channel more easily when it is open

Question 16

True or false: smaller axon diameter will increase conduction velocity.

Answer 16

False.

Larger diameter leads to increased velocit.

Question 17

How is AP conducted along an axon?

Answer 17

Change in MP causes a local current spread, which causes an immediate local MP change. If this threshold potential then an AP will fire.

Question 18

What 3 properties lead to a high conduction velocity of an axon?

Answer 18

1. High membrane resistance
2. Low membrane capacitance
3. Large diameterq

Question 19

What does low resistance suggest?

Answer 19

More channels are open, more local current lost.

Question 20

What is capacitance?

Answer 20

The ability to store charge

Question 21

High resistance means…

Answer 21

Fewer ion channels open, so less charge lost..

Question 22

Myelination of axons increases conduction velocity. How?

Answer 22

Reduces capacitance and increases resistance

Question 23

What 2 special cells form myelin?

Answer 23

1. Oligodendrocytes in CNS

2. Schwann cells in PNS

Question 24

What is saltatory conduction?

Answer 24

No AP needs to be generated in insulated, intermodal space, so it jumps between nodes of ranvier which have high density of Na+ channels.

Question 25

Give an example of a demyelinating disease.

Answer 25

Multiple Sclerosis.

Auto-immune disease which destroys myelin..decreasing conduction velocity or completely blocking AP transmission.

Question 26

What is a neuromuscular junction?

Answer 26

Synapse between a nerve and a skeletal muscle fibre.

Question 27

What channels are present at the nerve terminal?

Answer 27

Na+ channels, K+ channels and Ca2+ channels.

Question 28

What does depolarisation in the nerve terminal cause?

Answer 28

voltage gated calcium channels open, influx of calcium causes neurotransmitter release.

Question 29

How can you increase the amount of neurotransmitter released?

Answer 29

Increased frequency of action potentials. All the same size as all or nothing.

Question 30

Is the structure of the voltage gated calcium channel most similar to a Na+ channel or K+ channel?

Answer 30

Na+ channel. 1 polypeptide and 4 domains.

Question 31

What is MOA of dihydropyridines?

Answer 31

L-type calcium channel blocker. Decrease blood pressure.

Question 32

Which proteins are involved in the exocytosis of neurotransmitters?

Answer 32

Synaptotagmin - binds to the calcium and brings vesicle to membrane.
Snare complex- forms a fusion pore at membrane.

Question 33

Name a competitive nAChR blocker?

Answer 33

Tubocurarine

Question 34

name a depolarising nAChR blocker and outline its MOA.

Answer 34

Succinylcholine. It binds to the receptor and causes depolarisation, however it doesn’t dissociate, so the membrane cannot hyperpolarise again which means the Na+ channels cannot activate.

Question 35

What is myasthenia gravis?

Answer 35

Autoimmune disease targeting nACh receptors.