Lecture 6- The Action Potential

Question 1

What does the all or none principal of action potentials look like?

Answer 1

once threshold is reached the amplitude of the action potential is the same- the amplitude is NOT dependent on the strength of the stimulus

Question 2

How do we represent the strength of the stimulus?

Answer 2

frequency of firing

Question 3

What 2 factors influence conduction velocity?

Answer 3

1. degree of myelination

2. fiber diameter

Question 4

During the rising phase the sodium channels open and sodium rushes into the cell but the cell does not reach the equilibrium potential for sodium. Why is this so?

Answer 4

Because the K leak channels are releasing K and trying to pull the membrane voltage in the opposite direction

Question 5

What ion causes the inward current during the rising phase of the action potential?

Answer 5

Na- Sodium

Question 6

What are the two types of K channels on the cell membrane?

Answer 6

K leak channels-responsible for RMP

Voltage-gated K channels- responsible for repolarization stage of the AP

Question 7

What does TTX block?

Answer 7

Voltage gated Na channels

Question 8

What does TEA block?

Answer 8

Voltage gated K channels

Question 9

What is different about the voltage gated Na and K channels?

Answer 9

Na channel- opens quickly
- 2 gates

K channel- open with a delay
- 1 gate

Question 10

At rest what do the gates of the Na channel look like?

Answer 10

Activation closed

Inactivation open

Question 11

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

Answer 11

absolute RP- no channels available all are either inactivated or already open

relative RP- K channels still open, some Na available, can fire and AP but need a larger stimulus to overcome the greater distance from threshold