Characterizes an action potential?

Characterizes an action potential?

• A. A sustained depolarization with no threshold.
• B. A gradual depolarization without a repolarization phase.
• C. A rapid, all-or-none depolarization followed by repolarization, traversing the neuron.
• D. Hyperpolarization without any depolarization.

Answer: (C)

An action potential is an all-or-none, rapid depolarization that is followed by repolarization as it travels along the neuron. It starts when the membrane hits threshold, opening voltage-gated Na+ channels and letting Na+ rush in to drive the membrane from resting potential to a positive peak. Then those Na+ channels inactivate and K+ channels open, causing a quick repolarization back toward the resting potential, often with a brief hyperpolarization before settling. This sequence—threshold-triggered, rapid depolarization, then repolarization (and sometimes hyperpolarization)—is what allows the signal to propagate along the neuron without losing amplitude. The other descriptions describe gradual changes, lack the repolarization phase, or omit depolarization altogether, none of which match how an action potential actually occurs.

An action potential is an all-or-none, rapid depolarization that is followed by repolarization as it travels along the neuron. It starts when the membrane hits threshold, opening voltage-gated Na+ channels and letting Na+ rush in to drive the membrane from resting potential to a positive peak. Then those Na+ channels inactivate and K+ channels open, causing a quick repolarization back toward the resting potential, often with a brief hyperpolarization before settling. This sequence—threshold-triggered, rapid depolarization, then repolarization (and sometimes hyperpolarization)—is what allows the signal to propagate along the neuron without losing amplitude. The other descriptions describe gradual changes, lack the repolarization phase, or omit depolarization altogether, none of which match how an action potential actually occurs.