Question

what characterizes depolarization, the first phase of the action potential?
the membrane potential changes to a less negative (but not a positive) value.
the membrane potential changes to a much more negative value.
the membrane potential changes from a negative value to a positive value.
the membrane potential reaches a threshold value and returns to the resting state.

Explanation:

Depolarization is the first phase of an action potential. In a resting state, the membrane potential is negative (e.g., -70 mV in neurons). During depolarization, voltage - gated sodium channels open, and sodium ions ($Na^{+}$) rush into the cell. This influx of positive ions causes the membrane potential to become less negative and then positive. For example, in neurons, the membrane potential can go from -70 mV to +30 mV.

• The first option is incorrect because depolarization does not stop at a less - negative non - positive value.
• The second option is incorrect as depolarization is not about becoming more negative.
• The fourth option describes repolarization (returning to resting state) rather than depolarization.

Answer:

The membrane potential changes from a negative value to a positive value.