How does a signal travels down neuron?

Signal transmission down a neuron, known as an action potential, involves several key processes:

1. Resting Potential: Neurons maintain a resting potential, where the inside of the cell is negative relative to the outside. This difference in electrical potential is maintained by ion pumps, such as the sodium-potassium pump, that actively move ions across the cell membrane.

2. Depolarization: When a stimulus or signal reaches a neuron, it causes certain ion channels in the cell membrane to open. The most important of these channels are the sodium channels. When sodium channels open, sodium ions rush into the neuron, leading to a rapid depolarization of the membrane. This means the inside of the cell becomes less negative or more positive relative to the outside.

3. Action Potential: If the depolarization reaches a certain threshold, it triggers an action potential. During an action potential, the membrane potential of the neuron rapidly reverses, becoming more positive on the inside. This is also known as the "firing" of a neuron.

4. Sodium-Potassium Exchange: During an action potential, the opening of sodium channels allows sodium ions to enter the neuron, while the opening of potassium channels allows potassium ions to leave the neuron. The influx of sodium ions is responsible for the rapid depolarization, while the efflux of potassium ions helps repolarize the membrane back towards the resting potential.

5. Repolarization: After an action potential, the sodium channels close and the potassium channels remain open for a longer period. This allows more potassium ions to leave the neuron, causing the membrane potential to become more negative again. This process is called repolarization and restores the resting potential.

6. Hyperpolarization: In some cases, the membrane potential may become more negative than the resting potential after an action potential. This is called hyperpolarization. It results from a continued efflux of potassium ions and the activation of additional potassium channels.

7. Refractory Periods: Following an action potential, there are two refractory periods: the absolute refractory period and the relative refractory period. During the absolute refractory period, a neuron cannot generate another action potential, no matter how strong the stimulus. During the relative refractory period, an action potential can be generated, but it requires a stronger stimulus than usual. These refractory periods ensure that signals are transmitted in one direction down the neuron.

The sequence of depolarization, action potential generation, repolarization, and refractory periods allows electrical signals to propagate down the neuron, enabling communication between different parts of the nervous system.