Generation and Propagation of Action Potential in Neurons

How does a stimulus causes a voltage change in nerve cell?

When a stimulus is applied to a nerve cell, it can cause a voltage change known as an action potential. The process by which this occurs is called signal transduction.

Nerve cells, also known as neurons, have a specialized structure that allows them to transmit electrical signals. They have a cell membrane composed of a lipid bilayer that separates the inside of the cell from the outside environment. This membrane is selectively permeable, meaning it allows certain ions to pass through while blocking others.

At rest, the nerve cell has a resting membrane potential, which means there is a difference in electrical charge across the membrane. The inside of the cell is negatively charged compared to the outside. This resting potential is maintained by the activity of ion channels, which are proteins embedded in the cell membrane that control the flow of ions.

When a stimulus is applied to the nerve cell, it can generate an electrical signal. This stimulus could be mechanical, such as pressure or touch, or chemical, like a neurotransmitter binding to a receptor on the cell membrane. The stimulus causes certain ion channels in the membrane to open or close, allowing specific ions to flow in or out of the cell.

If the stimulus causes the opening of ion channels that allow positive ions, such as sodium (Na+), to enter the cell, it depolarizes the cell membrane. This means the inside of the cell becomes less negative or even positively charged compared to the outside. This depolarization is known as the action potential.

Once the cell reaches a certain threshold level of depolarization, it triggers a cascade of events. This includes the opening of more ion channels, particularly voltage-gated sodium channels. These channels rapidly open, allowing a significant influx of sodium ions into the cell. This sudden influx of positive ions further depolarizes the cell, creating a positive feedback loop.

As the positive charge spreads along the cell membrane, neighboring voltage-gated sodium channels are activated, leading to the propagation of the action potential along the nerve cell. This electrochemical signal allows the nerve cell to communicate with other cells in the body.

After the action potential passes through an area of the membrane, the voltage-gated sodium channels close and another set of ion channels, called voltage-gated potassium channels, open. These channels allow potassium (K+) ions to flow out of the cell, resulting in repolarization of the membrane and restoring the resting potential.

Overall, the stimulus causes a voltage change in nerve cells by altering the flow of ions across the cell membrane. This triggers the generation and propagation of an action potential, allowing the nerve cell to transmit electrical signals throughout the body.

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