 the neuromuscular junction connects the nervous system to the muscular system via synapses between efferent nerve fibers and muscle fibers, also known as muscle cells. as an action potential reaches the end of a motor neuron, voltage-dependent calcium channels open allowing calcium to enter the neuron. calcium binds to sensor proteins (synaptobrevin) on synaptic vesicles triggering vesicle fusion with the plasma 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 through the synapse and binds nicotinic acetylcholine receptors (nachrs) on the plasma membrane of the muscle fiber, also known as the sarcolemma. nachrs are ionotropic, 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. neuromuscular junction diseases can be of genetic and autoimmune origin. genetic disorders, such as duchenne muscular dystrophy, can arise from mutated structural proteins that comprise the neuromuscular junction, whereas autoimmune diseases, such as myasthenia gravis, occur when antibodies are produced against nicotinic acetylcholine receptors on the sarcolemma. ==structure== ===neuromuscular junction=== the neuromuscular junction is by definition a synapse, but it differs from synapses between neurons. presynaptic motor axons are demyelinated and stop 30 nanometers from the sarcolemma, the cell membrane of a muscle cell. this 30-nanometer space forms the synaptic cleft through which signalling molecules are released. the sarcolemma has invaginations called postjunctional folds, which increase the surface area of the membrane exposed to the synaptic cleft.{{cite book |author=nicholls, john g., |author2=a. robert martin |author3=paul a. fuchs |author4=david a. b
Neurophysiology Skeletal_muscle Somatic_motor_system