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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.
The electrical impulse travels along the pre-synaptic neurone axon to synapse with the muscle at the neuromuscular junction (NMJ) to cause muscle contraction. [17] When the action potential reaches the axon terminal, it triggers the opening of the calcium ion gated channels, which causes the influx of Ca 2+.
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. Neuromuscular junction ...
In order for a muscle to contract, an action potential is first propagated down a nerve until it reaches the axon terminal of the motor neuron. The motor neuron then innervates the muscle fibers to contraction by causing an action potential on the postsynaptic membrane of the neuromuscular junction.
The number of muscle fibers within each unit can vary within a particular muscle and even more from muscle to muscle: the muscles that act on the largest body masses have motor units that contain more muscle fibers, whereas smaller muscles contain fewer muscle fibers in each motor unit. [1]
Triads form the anatomical basis of excitation-contraction coupling, whereby a stimulus excites the muscle and causes it to contract. A stimulus, in the form of positively charged current, is transmitted from the neuromuscular junction down the length of the T tubules, activating dihydropyridine receptors (DHPRs).
Repetitive nerve stimulation is a variant of the nerve conduction study where electrical stimulation is delivered to a motor nerve repeatedly several times per second. By observing the change in the muscle electrical response (CMAP) after several stimulations, a physician can assess for the presence of a neuromuscular junction disease, and differentiate between presynaptic and postsynaptic ...
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]