**Question:** During the Repolarisation phase of Action Potential of a Neuron, which among the following takes place?

A. Hyperpolarization
B. Calcium-dependent potassium channels activation
C. Calcium influx
D. Sodium channels deactivation

**Correct Answer:** B. Calcium-dependent potassium channels activation

**Core Concept**

The action potential is a rapid change in cell membrane potential that propagates along the neurons due to the coordinated opening and closing of ion channels. The repolarization phase is a crucial part of the action potential, which restores the neuron to its resting membrane potential. Calcium-dependent potassium channels are involved in this process.

**Why the Correct Answer is Right**

During the repolarization phase, potassium ions (K+) need to be rapidly expelled from the neuron to restore the resting membrane potential. Calcium-dependent potassium channels are responsible for this process. These channels open when intracellular calcium ions (Ca2+) accumulate due to the activation of voltage-gated calcium channels during the depolarization phase. Calcium ions bind to the regulatory proteins, causing the opening of potassium channels. This rapid expulsion of K+ ions brings the membrane potential towards the resting state.

**Why Each Wrong Option is Incorrect**

A. Hyperpolarization: This option is incorrect because it describes a different phase of the action potential, specifically the depolarization phase. Hyperpolarization occurs when there is an influx of K+ ions, not the process we are discussing.

C. Calcium influx: This option is wrong because calcium influx occurs during the depolarization phase, not the repolarization phase. Calcium influx is necessary for the activation of calcium-dependent potassium channels, which are involved in repolarization.

D. Sodium channels deactivation: This option is incorrect as sodium channels are involved in the depolarization phase, not repolarization. Sodium channels close during repolarization, allowing potassium channels to open.

**Clinical Pearl**

Understanding the action potential and its phases is essential for understanding neural transmission and the functioning of neurons. This knowledge is crucial for physicians, surgeons, and other healthcare professionals, as it contributes to understanding the physiological processes in the central and peripheral nervous systems.