Voltage clamp

Question 1

purpose of voltage clamp

Answer 1

control the membrane potential to see which channel is open and how long does it take for it to open

Question 2

what happens when both membrane potential (Vm) and command voltage (Vc) = -70mV(only K+ channel)?

Answer 2

there is no different in current = no current output

Question 3

what happens when membrane potential (Vm) = -70mV and command voltage (Vc) = -10mV (only K+ channel)?

Answer 3

since there is a large difference -> large (+) current output (K+ efflux) -> make Vm become -10mV

Question 4

why does there is a increase current signal detect in the ammeter when membrane potential (Vm) = -70mV and command voltage (Vc) = -10mV?

Answer 4

since the Vm will be brought to -10mV due to K+ efflux -> there is a (+) charge injected to avoid Vm change

Question 5

according to the voltage clamp when Vm= -10mV, what is the direction of Na+ current?

Answer 5

Na+ current go inward (go down on ammeter graph)

Question 6

according to the voltage clamp when Vm= -10mV, what is the direction of K+ current?

Answer 6

K+ current go outward (go up on ammeter graph)

Question 7

according to the voltage clamp when Vm= -55mV, what is the direction of Na+ current?

Answer 7

Na+ current has no inward current (flat line in ammeter) because -55mV is equillibrium potential of Na too

Question 8

according to the voltage clamp when Vm= -55mV, what is the direction of K+ current?

Answer 8

K+ current has large outward current (go up on ammeter graph)

Question 9

what substance block Na+ channel?

Answer 9

TTX

Question 10

how does TTX affect the voltage clamp system?

Answer 10

block Na+ channel -> NO Na+ current in ammeter = inactivation gate close

Question 11

what substance block K+ channel?

Answer 11

TEA

Question 12

how does TEA affect the voltage clamp system?

Answer 12

Na+ inward current (go down) -> TEA block K+ channels = No outward K + current

Question 13

factor determine the conduction velocity of action potential

Answer 13

1. size of diameter
2. myelinate

Question 14

large diameter axons have _______ conduction velocities

Answer 14

fast

Question 15

The degree to which the current spreads down
the axon depends on two features:

Answer 15

1. internal resistance
2. membrane resistance

Question 16

internal resistance and membrane resistance become ___ as axon diameter increase

Answer 16

smaller

Question 17

although the diameter is large, why does only small amount of current pass down axon?

Answer 17

most current lost thru leakage since it take least resistance

Question 18

larger myelinated axons have _____ conduction velocities

Answer 18

faster

Question 19

how does damaged myelin in multiple sclerosis affect the action potential?

Answer 19

damaged myelin blocks signal from brain -> AP fail to propagated