Question

1. Why does the potassium conductance turn on more slowly and last longer than the sodium conductance?
2. When the membrane potential is depolarised sufficiently the action potential cease. This is the phenomena of spreading depression that occurs in the cerebral cortex and may underlie migraine headaches. Why are spontaneous APs generated?

3. How does the time course of recovery from Na+ channel inactivation compare to the time course of the refractory period following an action potential? Are these two processes related?

Answer 1

Q-1):

• Since the potassium channels are slower than the sodium channels, potassium starts flowing out of the cell only around the peak of the action potential, thereby hyperpolarizing the cell's membrane potential.

Q-3) :

• Therefore, when the Na⁺channels open and spontaneously inactivate, it takes time (several msec) for them to recover from that inactivation.
• This process of recovery from inactivation underlies the absolute refractory period.
• During an action potential the Na⁺channels open and then they become inactivated.

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