Why do Na+ ions enter the cell when voltage-gated Na+ channels are opened in neurons?
When voltage-gated Na+ channels are opened in neurons, Na+ ions enter the cell as a result of the electrical potential difference or voltage across the cell membrane. This process is essential for the generation and propagation of action potentials, which are the electrical signals that allow neurons to communicate with each other.
The opening of voltage-gated Na+ channels is triggered by depolarization of the cell membrane. When the neuron receives a strong enough stimuli, such as a neurotransmitter binding to a receptor, the membrane potential becomes less negative or even positive. This change in voltage causes the voltage-gated Na+ channels to undergo a conformational change, allowing Na+ ions to flow rapidly into the cell.
The influx of Na+ ions further depolarizes the cell membrane, leading to an increase in the positive charge inside the cell. This depolarization spreads along the neuron, creating an action potential. The entry of Na+ ions helps to propagate the action potential rapidly along the length of the neuron.
Furthermore, the opening of voltage-gated Na+ channels is transient, meaning they open for a short duration before inactivating. This inactivation prevents continuous influx of Na+ ions, limiting their entry into the cell and regulating the duration and amplitude of the action potential.