What occurs During Depolarization of an Axon? What occurs during depolarization of an axon? Multiple Choice
A Potassium channels open and potassium diffuses out of the cell.
B Potassium channels open and potassium diffuses into the cell.
C Sodium channels open and sodium diffuses into the cell.
D Sodium channels open and sodium diffuses out of the cell.
The Correct Answer and Explanation is :
The correct answer is C: Sodium channels open and sodium diffuses into the cell.
Explanation:
Depolarization of an axon is a crucial phase in the generation of an action potential, which is essential for neuronal communication. The process begins when a neuron is stimulated by a signal that raises the membrane potential, typically to a threshold level. This threshold is typically around -55 mV for most neurons.
Once the threshold is reached, voltage-gated sodium channels in the axon membrane open rapidly. Sodium (Na⁺) ions, which are more concentrated outside the neuron compared to the inside, start to flow into the cell due to both the concentration gradient and the electrical gradient. The influx of sodium ions causes the membrane potential to become less negative (more positive), leading to depolarization.
This rapid influx of sodium ions continues until the membrane potential approaches approximately +30 to +40 mV. At this point, the voltage-gated sodium channels begin to close, and the membrane potential is primarily influenced by potassium ions. This phase of depolarization is vital for the propagation of the action potential along the axon, allowing the nerve signal to travel quickly.
After depolarization, the axon enters the repolarization phase, where voltage-gated potassium channels open, allowing potassium ions to flow out of the cell. This outflow helps restore the membrane potential back to its resting state.
In summary, depolarization occurs when sodium channels open and sodium ions diffuse into the neuron, leading to a significant change in membrane potential. This process is essential for transmitting signals within the nervous system and is a fundamental concept in neurophysiology.