Question

2. Fill in the blank:

a) During the ________ phase of an action potential the membrane potential depolarizes to the signal peak with positive feedback. The initial depolarization was strong enough that enough voltage-gated sodium channels opened to cause more of a depolarization, which leads to even more depolarization.

b) At the _______ ________ of an action potential the maximum depolarization is reached. At this point more voltage-gated sodium channels are inactivating than are opening. Voltage-gated potassium channels may be starting to open.

c) During the _______ phase of an action potential the sodium channels are inactivating and voltage-gated potassium channels are opening.

Answer 1

(A) Depolarisation/ Rising Phase.

This is the first stage of an action potential in which the stimulus cause large number of voltage gated sodium channels to open causing influx of positive ions inside the cell. The membrane polarity is reversed i.e. becomes positive inside

(B) Peak of Action Potential

At this point the potential becomes too positive for sodium channels to remain open and hence they start closing i.e. there is no further rise in depolarization of the memberane.

(C) Repolarization/ falling phase

During this stage the sodium channels shut down and pottasium channels open causing net outward movement of positive ions leading to restoration of the normal membrane potential i.e. negative inside.