AP and voltage-gated ion channels

Question 1

What is depolarisation

Answer 1

Reduction in the difference of electrical potential across membrane nerve/ muscle cell. Excitatory signal. Potential becomes more positive inside cell

Question 2

What is hyperpolarisation

Answer 2

Increase in difference of electrical potential across membrane nerve/ muscle cell. Inhibitory signal. Potential becomes more negative inside cell

Question 3

Space constant

Answer 3

V=Voe^-x/lambda. V decays to 37% of Vo

Question 4

Solution to overcoming space constant

Answer 4

Myelin and APs

Question 5

What is an AP?

Answer 5

Same signal repeated very quickly on millisecond timescale (depol-hyperpol)

Question 6

What is myelin?

Answer 6

Formed by glial cells and increases resistance and decreases capacitance. Space constant increases. Velocity of AP increases by 20x

Question 7

What increases the frequency of APs?

Answer 7

The intensity of the stimulus

Question 8

All or none law

Answer 8

Small depolarising currents produce passive membrane response but larger current generates AP. Once AP generated, always full size

Question 9

Frequency code

Answer 9

Refractory period + threshold

Question 10

What is the absolute refractory period

Answer 10

When sodium channels are inactivated

Question 11

What is the relative refractory period

Answer 11

When potassium channels open

Question 12

Activation

Answer 12

Opening following depolarisation

Question 13

Inactivation

Answer 13

Closing independent of voltage

Question 14

Deactivation

Answer 14

Closing following hyperphosphorylation

Question 15

What does the speed of the AP depend on

Answer 15

How far the passive depolarisation spreads

Question 16

Why are membrane channels needed

Answer 16

Membrane acts as energy barrier for ion crossing

Question 17

Multiple Sclerosis

Answer 17

Episodic autoimmune destruction of myelin surrounding CNS (poor nerve conduction)

Question 18

Patch clamping

Answer 18

Glass electrode with very fine tip placed over individual channel. Systematically change voltage using amplifier

Question 19

How many coding genes code for ion channel subunits

Answer 19

10%

Question 20

How do channels open?

Answer 20

Mechanical force, temperature, change in voltage, ligand binding

Question 21

Voltage-gated sodium channel

Answer 21

Single proteins spreads through membrane 4 times. Re-enterent pore loop. TM4 = voltage sensor. Tetramer. K+ too big to pit into channel.

Question 22

K+ conduction rate

Answer 22

10^7-10^78 ions per second

Question 23

K+ leak channel

Answer 23

Open. Tetramer. Potassium ions interact with carbonyl groups of TVGYG sequence of selectivity pore

Question 24

Saltatory conduction

Answer 24

Myelin and nodes of ranvier. Space constant increases