Presynaptic Neuron

The presynaptic (before the synapse) neuron, a specialized cell found at the axon terminal, contains synaptic vesicles which house/release neurotransmitters (chemical messengers) — when stimulated by an action potential (electrical signal) — into the synaptic cleft. Presynaptic faces postsynaptic neuron across the synapse. The presynaptic membrane contains specialized protein complexes (multiple proteins forming a functional unit), called “active zones,” where synaptic vesicles dock/fuse to release the neurotransmitters. Also essential to sending neuron-to-neuron signals are high concentrations of voltage-gated calcium channels (CaV) — proteins that penetrate the plasma membrane to allow calcium ions to flow into the cell and trigger the release of neurotransmitters.