In what part of the neuron does the action potential begin?

The action potential begins at the axon hillock. This is a specialized region located at the junction of the cell body (soma) and the axon. The axon hillock is crucial for the initiation of action potentials because it contains a high density of voltage-gated sodium channels. When a neuron receives sufficient excitatory input, it causes a depolarization that reaches a threshold level at the axon hillock. Once this threshold is reached, an action potential is generated, allowing electrical signals to propagate down the length of the axon toward the axon terminals.

The dendrites primarily function to receive signals from other neurons and are involved in synaptic transmission, but they do not initiate action potentials. The soma, while containing the nucleus and metabolic machinery of the neuron, does not typically initiate action potentials either. The axon terminal is the endpoint of the axon where neurotransmitter release occurs; it plays a role in communicating with other neurons but does not participate in the generation of action potentials. Thus, the axon hillock is critical because it is the site where the decision to fire an action potential is made based on the input received by the neuron.