<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>
<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 neurotransmitter that is active at the neuromuscular junction is
the neurotransmitter that is active at the neuromuscular junction is
acetylcholine
acetylcholine