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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 opposite can happen when the opening of ion channels results in the flow of negatively charged ions, like chloride (Cl −), into the cell, or positively charged ions, like potassium (K +), to flow out of the cell, creating inhibitory postsynaptic potentials (IPSP) that hyperpolarize the cell membrane, decreasing the likelihood of an action ...
In some invertebrates, glutamate is the main excitatory transmitter at the neuromuscular junction. [3] [4] In the neuromuscular junction of vertebrates, EPP (end-plate potentials) are mediated by the neurotransmitter acetylcholine, which (along with glutamate) is one of the primary transmitters in the central nervous system of invertebrates. [5]
If the postsynaptic cell (B) is also a neuron, neurotransmitter receptors generate a small electrical current that changes the postsynaptic potential. If the postsynaptic cell (B) is a muscle cell ( neuromuscular junction ), it contracts.
A special case of a chemical synapse is the neuromuscular junction, in which the axon of a motor neuron terminates on a muscle fiber. [ae] In such cases, the released neurotransmitter is acetylcholine, which binds to the acetylcholine receptor, an integral membrane protein in the membrane (the sarcolemma) of the muscle fiber.
Visceral efferent neurons innervate smooth muscle, cardiac muscle, and glands, and have the ability to be either excitatory or inhibitory in function. Neuroeffector junctions are known as neuromuscular junctions when the target cell is a muscle fiber. Non-synaptic transmission is characteristic of autonomic neuroeffector junctions.
This produces a greater force than singular contractions by decreasing the interval between stimulations to produce a larger force with the same number of motor units. Using electromyography (EMG), the neural strategies of muscle activation can be measured. [6]
These levels are maintained via the recycling of glutamate molecules in the neuronal-glial cell process known as the glutamate–glutamine cycle, in which glutamate is synthesized from its precursor glutamine in a controlled manner in order to maintain an adequate supply of the neurotransmitter. [3]