<Tr> <Th> FMA </Th> <Td> 61803 </Td> </Tr> <Tr> <Td_colspan="2"> Anatomical terminology (edit on Wikidata) </Td> </Tr> <P> A neuromuscular junction (or myoneural junction) is a chemical synapse formed by the contact between a motor neuron and a muscle fiber . It is at the neuromuscular junction that a motor neuron is able to transmit a signal to the muscle fiber, causing muscle contraction . </P> <P> Muscles require innervation to function--and even just to maintain muscle tone, avoiding atrophy . Synaptic transmission at the neuromuscular junction begins when an action potential reaches the presynaptic terminal of a motor neuron, which activates voltage - dependent calcium channels to allow calcium ions to enter the neuron . Calcium ions bind to sensor proteins (synaptotagmin) on synaptic vesicles, triggering vesicle fusion with the cell membrane and subsequent neurotransmitter release from the motor neuron into the synaptic cleft . In vertebrates, motor neurons release acetylcholine (ACh), a small molecule neurotransmitter, which diffuses across the synaptic cleft and binds to nicotinic acetylcholine receptors (nAChRs) on the cell membrane of the muscle fiber, also known as the sarcolemma . nAChRs are ionotropic receptors, meaning they serve as ligand - gated ion channels . The binding of ACh to the receptor can depolarize the muscle fiber, causing a cascade that eventually results in muscle contraction . </P>

The function of the neuromuscular junction is to