Neuromuscular junction and motor unit
The neuromuscular junction is a site where a motor neuron meets a skeletal muscle fiber. It is where a nerve impulse is transmitted from a motor neuron to a muscle fiber. A neuromuscular junction is made up of a nerve terminal, which contains the neurotransmitter acetylcholine, and a muscle fiber, which has receptors for acetylcholine.
When an action potential reaches the nerve terminal, it causes the release of acetylcholine, which diffuses across the synapse and binds to receptors on the muscle fiber. This activates an ion channel, allowing ions to flow into the muscle fiber and causing it to depolarize. This depolarization triggers the release of calcium ions from intracellular stores, which initiates the contraction of the muscle.
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