Threshold potential refers to the membrane potential required to:

A. initiate an action potential and open voltage-gated sodium ion channels.

B. initiate an action potential.

C. open voltage-gated sodium ion channels.

D. open voltage-gated potassium ion channels.

B. initiate an action potential

Explanation:

Threshold potential is the critical level to which a membrane potential must be depolarized to begin an action potential. In the study of the structure or function of the nervous system and brain, threshold potentials are necessary to control and propagate signaling in both the central nervous system (CNS) and the peripheral nervous system (PNS).

B. initiate an action potential.

Action potentials are initiated when a depolarization reaches a threshold potential. This threshold potential varies, but is normally around 55 or 50 millivolts above the resting potential of the cell, which implies that the input current of sodium ions exceeds the output current of potassium ions.