Action Potential

Question 1

Current Clamp

Answer 1

Volts

measures the membrane potential (difference in charge across the membrane)

control amount of current injected to see how membrane potential responds

Question 2

Voltage Clamp

Answer 2

measures net current flow across a membrane (how quickly is charge getting through the membrane?)

keep neuron at fixed voltage to see how current responds

V = IR

Question 3

Depolarization

Answer 3

change in the membrane potential from the value at rest to a less negative value (-65 →-60)

making it more excitable

Question 4

Hyperpolarization

Answer 4

change in the membrane potential from the value at rest to a more negative value (ex. -65 →-70)

making it less excitable

Question 5

Voltage-gated channels

Answer 5

• open when there’s a depolarization
• closed @rest → depol → open @threshold
• positive charges on gate are repelled when inside membrane becomes more positive → causes conformational change

Question 6

V-gated Na+ vs. V-gated K+ channels

Answer 6

V-gated Na+

• open quickly
• inatviate relatively quickly (“ball & chain mechanism)
• deinactivtion w/slight delay after going back to resting V_M

_​V-gated K+

• open with a delay
• no inactivation
• close w/slight delay at resting Vm

Question 7

AP steps

Answer 7

1. Resting state = both channels closed
2. Depolarization = to threshold
3. Rising phase = Na+ channels open, large Na+ driving force → causes depol
4. Falling phase = large driving force for K+; ball & chain on Na+ channels act as ball and chain
5. Undershoot

Question 8

Significance of P_K: P_Na ratio being the highest during falling phase in AP

Answer 8

this means more K+ is going thru bc channels are open; Na+ channels are closed

Question 9

We know Na+ and K+ currents generate AP’s bc…

Answer 9

ion concentration is not changing during an action potential

Question 10

Voltage Clamp

Answer 10

Na current is depolarizing (negative current)

K current is hyperpolarizing (positive current)

Question 11

TTX

Answer 11

toxin that blocks V-gated Na channels

AP wouldn’t happen - would go almost to threshold and go back down

Question 12

TEA

Answer 12

toxin that blocks V-gated K channels

would have a larger and longer AP, wouldnt have an undershoot (would go back to threshold and stop)

Question 13

Refractory Period

(absolute and relative)

Answer 13

time when we can’t get another AP

absolute refractory → can’t get another AP no matter what

• when all Na+ channels inactivated; in the middle of the falling phase

relative refractory → we can get another AP with enough depol

• some Na+ channels deinactivated; happens during undershoot

Question 14

Steps of AP (channels)

Answer 14

1. @rest → V-gated Na closed
2. depol → V-gated Na open
3. rising → V-gated K open (right before peak)
4. peak → V-gated Na inactivated
5. undershoot → V-gated Na channels deinactivated, K channels close