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A neuromuscular junction (or myoneural junction) is a chemical synapse between a motor neuron and a muscle fiber. [1] It allows the motor neuron to transmit a signal to the muscle fiber, causing muscle contraction. [2] Muscles require innervation to function—and even just to maintain muscle tone, avoiding atrophy.
It is the site in which a motor neuron transmits a signal to a muscle fiber to initiate muscle contraction. The sequence of events that results in the depolarization of the muscle fiber at the neuromuscular junction begins when an action potential is initiated in the cell body of a motor neuron, which is then propagated by saltatory conduction ...
When necessary, the maximal number of motor units in a muscle can be recruited simultaneously, producing the maximum force of contraction for that muscle, but this cannot last for very long because of the energy requirements to sustain the contraction. To prevent complete muscle fatigue, motor units are generally not all simultaneously active ...
Note the differences in the scales on the X- and Y-axes. Both are taken from recordings at the mouse neuromuscular junction. End plate potentials (EPPs) are the voltages which cause depolarization of skeletal muscle fibers caused by neurotransmitters binding to the postsynaptic membrane in the neuromuscular junction. They are called "end plates ...
These impulses move to the neuromuscular junction (NMJ) of skeletal muscle via peripheral axons after synapsing with the lower motor neurons through the ventral horn of the spinal cord. A signal that travels to the NMJ, which innervates muscles, is produced by the release of acetylcholine by upper motor neurons.
Neuromuscular junction diseases are a result of a malfunction in one or more steps of the above pathway. As a result, normal functioning can be completely or partially inhibited, with the symptoms largely presenting themselves as problems in mobility and muscle contraction as expected from disorders in motor end plates.
(b) A functional electrical stimulation system injects electrical current into the cell. (c) The intact but dormant axon receives the stimulus and propagates an action potential to (d) the neuromuscular junction. (e) The corresponding muscle fibers contract and generate (f) muscle force. (g) A train of negative pulses is produced.
Muscle fatigue is the neuromuscular adaptation to challenges over a period of time. The use of motor units over a period of time can result in changes in the motor command from the brain. Since the force of contraction cannot be changed, the brain instead recruits more motor units to achieve maximal muscle contraction. [22]