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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 compound muscle action potential (CMAP) is the resulting response and depends on the motor axons transmitting the action potential, the status of the neuromuscular junction, and muscle fibers. The CMAP amplitudes, motor onset latencies, and conduction velocities are routinely assessed and analyzed.
A neuroeffector junction is a site where a motor neuron releases a neurotransmitter to affect a target—non-neuronal—cell. This junction functions like a synapse . However, unlike most neurons, somatic efferent motor neurons innervate skeletal muscle, and are always excitatory.
Neuromuscular junction diseases in this category include snake venom poisoning, botulism, arthropod poisoning, organophosphates and hypermagnesemia.(reference 13) Organophosphates are present in many insecticides and herbicides. They are also the basis of many nerve gases.(reference 27) Hypermagnesmia is a condition where the balance of ...
Nerve conduction studies can only diagnose diseases on the muscular and nerve level. They cannot detect disease in the spinal cord or the brain. In most disorders of the muscle, nerve, or neuromuscular junction, the latency time is increased. [12] This is a result of decreased nerve conduction or electrical stimulation at the site of the muscle.
In addition, a synapse serves as a junction where both the transmission and processing of information occur, making it a vital means of communication between neurons. [ 11 ] At the synapse, the plasma membrane of the signal-passing neuron (the presynaptic neuron) comes into close apposition with the membrane of the target ( postsynaptic ) cell.
Neuromuscular disease can also be diagnosed by various blood tests and using electrodiagnostic medicine tests [23] including electromyography [24] (measuring electrical activity in muscles) and nerve conduction studies. [25] Genetic testing is an important part of diagnosing inherited neuromuscular conditions. [23]
Each gap junction (sometimes called a nexus) contains numerous gap junction channels that cross the plasma membranes of both cells. [11] With a lumen diameter of about 1.2 to 2.0 nm, [2] [12] the pore of a gap junction channel is wide enough to allow ions and even medium-size molecules like signaling molecules to flow from one cell to the next, [2] [13] thereby connecting the two cells' cytoplasm.