What cation (positive charged ion) rushes into the cell during depolarization period of action potential?

The cation that rushes into the cell during the depolarization period of an action potential is Sodium (Na+). Here are the steps explaining the process:

1. At rest, the neuron has a negative charge inside relative to the outside. This is due to the distribution of different ions, including Sodium (Na+) and Potassium (K+), across the neuron's membrane.

2. When a stimulus is received, voltage-gated Sodium channels open. This means that the channels that were keeping Sodium ions out of the cell now open up.

3. Sodium ions, which are positively charged, rush into the cell. This is due to the concentration gradient - there are more Sodium ions outside the cell than inside, so they move into the cell to balance this out.

4. The influx of positive Sodium ions makes the inside of the cell more positive, causing the cell to depolarize.

5. Once the cell reaches a certain level of depolarization, known as the threshold, an action potential is triggered. This is a rapid, temporary change in the membrane potential.

6. After the action potential, the cell repolarizes - it returns to its resting state. This is achieved by the opening of voltage-gated Potassium channels, allowing Potassium ions to leave the cell, and the closing of Sodium channels, preventing more Sodium ions from entering the cell.