When an electrical impluse travels along a motor neuron and arrives at a neuromuscular junction what happens?

Answer 1

Calcium enters through the voltage-gate and triggers the release of transmitter.

" the entry of calcium through voltage-gated calcium channels causes synaptic vesicles to fuse with the presynaptic plasma membrane and release the neurotransmitter acetylcholine into the synaptic cleft. Acetylcholine diffuses across the cleft and binds to muscle acetylcholine receptors, causing depolarization and an action potential that travels throughout the length of the muscle cell triggering muscle contraction. "

Answer 2

An action potential is generated in the sarcolemma(cell membrane of a muscle fiber), resulting in the contraction of that muscle fiber, when an electrical impulse traveling along an axon of a motor neuron arrives at a neuromuscular junction (synapse).

The neuromuscular junction is a synapse or connection point between a motor neuron's axon terminal and a muscle cell. When an electrical (ionic) impulsetraveling along a motor neuron's axon reaches the axon terminal, voltage-gated calcium ion channels (pores) are caused to open in the axon terminal, allowing an influx of calcium ions, which cause vesicles (small bags) containing neurotransmitters to fuse with the cell membrane at the axon terminal, releasing those neurotransmitters into the synaptic cleft (in the case of the neuromuscular junction, the neurotransmitter is acetylcholine), in a process known as exocytosis (which simply means that something inside the cell is caused to go outside the cell).

The acetylcholine (ACh) diffuses across the synapse and is taken up by ACh receptors, which, as ligand-gated ion pores, allow an initial influx of sodium ions into the muscle cell, which causes nearby voltage-gated sodium ion pores to open, allowing more sodium in, which causes successive nearby v-gated sodium ion pores to open, resulting in a propagation of an action potentialalong the muscle cell, resulting in it's contraction.

The contraction of a muscle cell (fiber) is a matter of small filaments being caused to slide past one another by the action potential.

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