What occurs when a neuron reaches a threshold of approximately -55 mV?

When a neuron reaches a threshold of approximately -55 mV, it triggers an action potential. This is a critical moment in neuronal communication. The threshold potential signifies the point at which the voltage-gated sodium channels in the neuron's membrane open. This rapid influx of sodium ions into the cell causes a significant change in the membrane potential, leading to depolarization. As the membrane depolarizes, it typically reaches a peak around +30 to +40 mV, which is essential for propagating the electrical signal along the axon to communicate with other neurons or muscles.

This process is fundamental in the functioning of neurons, as the generation of an action potential allows for the transmission of signals over long distances within the nervous system. Upon firing, the neuron enters a phase where it cannot immediately fire another action potential, also known as the refractory period, but that occurs after the action potential has already been generated, not at the moment the threshold is reached. Understanding this mechanism is crucial for grasping how nervous system signaling operates.