a nerve impulse triggers the release of acetylcholine at a neuromuscular junction.
a nerve impulse triggers the release of what chemical at a neuromuscular junction?
acetylcholine
in normal neuromuscular function, a nerve impulse is carried down the axon (the long projection of a nerve cell) from the spinal cord. at the nerve ending in the neuromuscular junction, where the impulse is transferred to the muscle cell, the nerve impulse leads to the opening of voltage-gated calcium channels (vgcc), the influx of calcium ions into the nerve terminal, and the calcium-dependent triggering of synaptic vesicle fusion with plasma membrane. these synaptic vesicles contain acetylcholine, which is released into the synaptic cleft and stimulates the acetylcholine receptors on the muscle. the muscle then contracts.
lambert–eaton myasthenic syndrome
the release of a neurotransmitter is triggered by the arrival of a nerve impulse (or action potential) and occurs through an unusually rapid process of cellular secretion (exocytosis). within the presynaptic nerve terminal, vesicles containing neurotransmitter are localized near the synaptic membrane. the arriving action potential produces an influx of calcium ions through voltage-dependent, calcium-selective ion channels at the down stroke of the action potential (tail current). calcium ions then bind to synaptotagmin proteins found within the membranes of the synaptic vesicles, allowing the vesicles to fuse with the presynaptic membrane. the fusion of a vesicle is a stochastic process, leading to frequent failure of synaptic transmission at the very small synapses that are typical for the central nervous system. large chemical synapses (e.g. the neuromuscular junction), on the other hand, have a synaptic release probability of 1. vesicle fusion is driven by the action of a set of proteins in the presynaptic terminal known as snares. as a whole, the protein complex or structure that mediates the docking and fusion of presynaptic vesicles is called the active zone. the membrane added by the fusion process is later retrieved by endocytosis and recycled for the formation of fresh neurotransmitter-filled vesicles.
chemical synapse