ABSTRACT
Neuromuscular transmission occurs through the release of acetylcholine at the motor endplate by motor neurones leading to the muscular contraction process. Both nerve and muscle cells can generate action potentials. Action potential, however, cannot propagate across the neuromuscular junction: transmission from nerve to muscle occurs through the medium of acetylcholine which is released into the synaptic cleft when the action potential reaches the nerve terminal. Acetylcholine binds to nicotinic acetylcholine receptors at the endplate, and causes the ion channel of the receptor to open. This makes the membrane potential less negative, that is a depolarisation occurs. When depolarisation reaches the threshold voltage, a muscle action potential is initiated, leading to muscular contraction
NEUROMUSCULAR JUNCTION
Each motor neurone runs as a large myelinated axon without interruption from the anterior horn of the grey matter in the spinal cord to the neuromuscular junction. A single axon innervates many muscle fibres. With a few exceptions (extraocular muscles and the upper oesophagus), human muscle cells are each innervated by a single axon. The axon, together with the muscle fibres that it innervates, is called a motor unit. The number of muscular fibres innervated by a single neurone ranges from 3 to 1000, depending on the muscular function. Small muscles that react rapidly and whose control must be exact, such as the extraocular muscles and the muscles controlling the fingers, have few muscles in each motor unit. In contrast, large muscles that do not require fine control, such as the gastrocnemius, may have several hundred muscle fibres in their motor units.
