During repolarization of nerve

Options

A. `Na^(+)` channels are closed and `K^(+)` channel are open
B. `K^(+)` gate closes and `Na^(+)` gate open
C. Both `K^(+)` and `Na^(+)` gates are closed
D. Both gates remain open

Answer

### Step-by-Step Solution

1. **Understanding Neuron Function**: Neurons are the functional units of the nervous system responsible for transmitting signals. They communicate between the brain and various body parts.

**Hint**: Remember that neurons are specialized cells that transmit electrical signals.

2. **Resting Membrane Potential**: At rest, a neuron has a resting membrane potential of approximately -70 mV. This means the inside of the neuron is negatively charged compared to the outside.

**Hint**: The resting membrane potential is crucial for the generation of action potentials.

3. **Depolarization Phase**: When a neuron receives a stimulus, it undergoes depolarization. This occurs when sodium (Na+) channels open, allowing sodium ions to flow into the neuron, making the inside more positive.

**Hint**: Depolarization is the process where the membrane potential becomes less negative (more positive).

4. **Repolarization Phase**: After depolarization, the neuron needs to return to its resting state, which is known as repolarization. During this phase, sodium channels close, and potassium (K+) channels open.

**Hint**: Repolarization is essential for restoring the resting membrane potential after an action potential.

5. **Potassium Ion Movement**: As potassium channels open, potassium ions flow out of the neuron. This movement of positive ions out of the cell helps to bring the membrane potential back down towards the resting level.

**Hint**: The outflow of potassium ions is what helps to repolarize the neuron.

6. **Hyperpolarization**: Sometimes, the potassium channels remain open longer than necessary, causing the membrane potential to become even more negative than the resting potential. This state is known as hyperpolarization.

**Hint**: Hyperpolarization can make it more difficult for the neuron to fire again immediately.

### Summary
During repolarization of a nerve, sodium channels close, potassium channels open, and potassium ions exit the neuron, leading to a return towards the resting membrane potential. If potassium channels remain open too long, hyperpolarization may occur.