The absolute refractory period of a neuron
a. is due to the high negative polarity of the inside of the neuron.
b. occurs only during the repolarization phase.
c. occurs only during the depolarization phase.
d. occurs during depolarization and the first part of the repolarization phase.
The Correct Answer and Explanation is :
The correct answer is d. occurs during depolarization and the first part of the repolarization phase.
Explanation:
The absolute refractory period is a critical phase in the action potential of a neuron. It refers to the period during which a neuron cannot fire another action potential, no matter how strong the stimulus is. This period is a direct result of the behavior of ion channels during the action potential.
- Depolarization Phase: During the depolarization phase of the action potential, sodium (Na⁺) channels open, allowing sodium ions to rush into the neuron, which causes the inside of the cell to become more positive. As the membrane potential reaches a certain threshold, the neuron fires an action potential. However, once the sodium channels open, they quickly enter an inactive state, preventing them from opening again immediately. This inactivation of sodium channels contributes to the absolute refractory period, as the neuron cannot be re-stimulated during this time.
- Repolarization Phase: As the action potential progresses, potassium (K⁺) channels open to allow potassium ions to exit the neuron, which begins the repolarization phase (the cell’s interior becomes negative again). While potassium channels are open and sodium channels remain inactivated, the neuron is still unable to fire another action potential, thus continuing the absolute refractory period. This period lasts until the sodium channels return to their resting (closed) state, which typically occurs by the end of the repolarization phase.
The absolute refractory period prevents the neuron from firing too frequently and ensures the unidirectional propagation of the action potential. It also allows the neuron time to return to its resting state. Following the absolute refractory period, the relative refractory period begins, during which a stronger-than-normal stimulus is required to generate another action potential.
In summary, the absolute refractory period encompasses both the depolarization phase and the initial part of the repolarization phase, ensuring that action potentials do not overlap and that the nerve can recover before being stimulated again.