An action potential is regarded as an example of a positive feedback. Which of the following examples below best illustrates the positive feedback aspect of an action potential?
A) Potassium permeability is about 25 times greater than sodium ions.
B) Voltage gated potassium ion channels open slowly and remain open long enough to cause hyperpolarization.
C) A threshold stimulus will cause the opening of voltage gated sodium ion channels that will cause further depolarizing stimulus. This stimulus will open still more voltage gated sodium ion channels.
D) The sodium potassium pump consistently moves ions as long as ATP is available, and regardless of membrane potential changes.

Question

Quizplus · Accepted Answer

Positive feedback is a process in which an initial stimulus produces a response that amplifies or reinforces the original stimulus. In the case of an action potential, the initial depolarization stimulus opens some voltage-gated sodium ion channels, causing an influx of sodium ions, which further depolarizes the membrane and opens more voltage-gated sodium ion channels, causing even more sodium ions to enter the cell. This leads to a rapid and large depolarization, which is characteristic of positive feedback. Potassium permeability and the sodium-potassium pump are not examples of positive feedback, and while the opening of voltage-gated potassium ion channels does cause hyperpolarization, it does not contribute to the positive feedback of the initial depolarization stimulus.

An Action Potential Is Regarded as an Example of a Positive