An action potential is self-regenerating because __.
A- depolarizing currents established by the influx of K+ flow down the axon and trigger an action potential at the next segment
B- repolarizing currents established by the efflux of Na+ flow down the axon and trigger an action potential at the next segment
C- depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segment
D- repolarizing currents established by the efflux of K+ flow down the axon and trigger an action potential at the next segment
The Correct Answer and Explanation is:
The correct answer is C- depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segment.
Explanation
An action potential is a rapid, transient change in the membrane potential of a neuron, which occurs when a stimulus causes the membrane to become depolarized. This depolarization is primarily due to the influx of sodium ions (Na⁺) through voltage-gated sodium channels in the neuron’s membrane. The process of generating and propagating an action potential is self-regenerating due to the following mechanisms:
- Initiation of the Action Potential: When a neuron’s membrane potential reaches a certain threshold (usually around -55 mV), voltage-gated sodium channels open, allowing Na⁺ to flow into the cell. This influx causes the membrane potential to become more positive, leading to rapid depolarization.
- Propagation Along the Axon: As the membrane depolarizes at one segment of the axon, it creates a local depolarizing current that flows to adjacent segments of the membrane. This current is due to the concentration gradient established by the influx of Na⁺. The positive charges from the depolarized area flow toward the adjacent, still resting segment of the membrane, raising its membrane potential toward the threshold for action potential generation.
- Triggering Subsequent Action Potentials: When the adjacent segment of the membrane reaches the threshold potential due to the depolarizing current, voltage-gated sodium channels open there as well, resulting in a new influx of Na⁺ and the generation of a new action potential at that segment. This self-regenerative process continues along the length of the axon, allowing the action potential to propagate rapidly.
- Role of Repolarization: After the peak of the action potential, voltage-gated sodium channels close and voltage-gated potassium channels open, allowing K⁺ to exit the cell. This efflux repolarizes the membrane back toward its resting potential but does not directly contribute to the regeneration of the action potential. Instead, it resets the membrane potential, preparing it for the next potential action.
In summary, the self-regenerating nature of action potentials is primarily driven by the depolarizing currents established by the influx of Na⁺, which propagate along the axon and trigger successive action potentials in adjacent segments.