Introduction to the Neuromuscular Junction
While the synapse is the "connection" between two neurons, the neuromuscular junction is the "connection" between a motor neuron and a striated muscle fiber.
In general terms, the neuromuscular junction and the synapse are physiologically identical.
Synaptic vesicles in the enlarged bouton of the motor neuron contain the neurotransmitter acetylcholine (ACH).
As an impulse reaches the bouton, ACH is released and passes through the presynaptic membrane into the synaptic cleft.
The surface of the postsynaptic membrane is in a series of longitudinal folds.
This greatly increases the surface area receptive to the ACH.
The Motor Unit
The motor unit is the group of striated muscle fibers innervated by the terminal arborization (tree-like branching) of one motor neuron.
The fewer the muscle fibers found per motor unit, the more the muscle is capable of finer movements.
As the number in the motor unit increases, the muscle action is coarser.
When a muscle is to be used, the nervous system recruits just enough motor units to supply the strength
needed for the work to be done.
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