What primarily occurs at synapses in the nervous system?

At synapses in the nervous system, the primary event is the release of neurotransmitters. Synapses are specialized junctions where communication between neurons occurs. When an action potential reaches the end of a neuron (the presynaptic terminal), it triggers the release of neurotransmitters stored in vesicles. These neurotransmitters then cross the synaptic cleft and bind to receptors on the postsynaptic neuron, influencing whether that neuron will become activated (or depolarized). This process is fundamental to neuronal communication and is critical for functions such as mood regulation, reflexes, and all complex brain activities.

Other processes like initiating neural impulses, axon regeneration, and myelination of axons, occur at different points and involve different mechanisms within the nervous system, but they do not primarily happen at synapses. Axon regeneration and myelination are also associated with structural and functional support, while the initiation of neural impulses pertains to the generation of action potentials along the axon rather than at the synaptic junction itself. Thus, neurotransmitter release is the key activity that occurs at synapses, enabling the signaling between neurons.