What happens during the depolarization phase of nerve cells?
A) It is an undisturbed period of the action potential during which the nerve is not transmitting impulses.
B) The cell membrane decreases its permeability to sodium.
C) The neurons are stimulated to fire.
D) A rapid change in polarity to one that is positive on the inside and the membrane becomes open to sodium.
Ans: D
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Depolarization is characterized by a rapid change in polarity of the resting membrane potential, which was negative on the inside and positive on the outside, to one that is positive on the inside and negative on the outside. During the depolarization phase, the membrane suddenly becomes permeable to sodium ions. The rapid inflow of sodium ions produces local electric currents that travel through the adjacent cell membrane, causing the sodium channels in this part of the membrane to open. The resting membrane potential is the undisturbed period of the action potential during which the nerve is not transmitting impulses. A threshold potential represents the membrane potential at which neurons or other excitable tissues are stimulated to fire.
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