L5 Excitable cell Part - 2 X

Answer 1

Difference

Question 2

What is the IDF proportional to?

Answer 2

It’s proportional to the difference between Vm and E(ion)

Question 3

What does IDF stand for?

Answer 3

Ionic driving force

Question 4

What are the standard units for action potential?

Answer 4

mV

Question 5

What are the properties of the action potential?

Answer 5

1. Transient, rapid and reversible channge in membrane potential form negative to positive.
2. Different types of excitable cells may have different types of action potential.
3. Neuron AP often triggered by Na+ permeability increase.
4. AP’s or spikes generated by a cell.

Question 6

What are the changes in membrane permeability that underlie an action potential?

Answer 6

• The sodium ion channel open so permeability for sodium ions increase (depolarisation to 0 and above) Inside the cell
• Na+ channels shuts and permeability to K+ dominates again

Question 7

When does the sodium channels open?

Answer 7

They open when the membrane is depolarised.

Question 8

What is the structure of the voltage - gated Na+ channels?

Answer 8

6 transmembrane domains
Has a pore loop
Has a selectivity filter
Has a voltage sensor gate

Question 9

How fast does channel inactivation occur?

Answer 9

1ms

Question 10

What does opening of voltage gated pottasium channels lead to?

Answer 10

Leads to repolarization.

Question 11

What poison blocks K+ channels ?

Answer 11

Tetraethylammonium, TEA

Used as anaesthetic.

Question 12

What poison blocks Na+ channels?

Answer 12

Tetrodotoxin, TTX

Pufferfish

Question 13

Explain the 5 phases

Answer 13

1. Threshold - Opening od sufficient voltage gated Na+ channels enabling Na+ to K+ perembility.
2. Rising Phase - Rapid depolarization caused by a large forces drives Na+ into neurons.
3. Overshoot - Vm reaches ENa.
4. Falling Phase - Na+ channels(Inactivate), K+ Channels(Open), driving K+ out of neuron.
5. Undershoot - voltage-gated K+ channels (delayed rectifiers) add to resting K+ membrane permeability and reduced Na+ permeability so Vm ~ EK

Question 14

How does an action potential conduction travel in one direction?

Answer 14

Action potential occurs by spread of charged particles (the Na+ ions) although they spread in both directions, Na channels behind inactivated, so only Na channels ahead available to open…hence why action potential travels in one direction from point of initiation.

Question 19

What is Cv?

Answer 19

Conducting velocity

Question 20

What are the factors that influence conducting velocity?

Answer 20

The diameter of the axon
Myelin still of the axon

Question 21

Why would the diameter of the axon