neuromuscular junction excitatory synapse excitatory neuromuscular junction dos The junction between the axon of a motor neuron and a muscle fiber. In response to the arrival of action potentials, the presynaptic button releases molecules of neurotransmitters into the synaptic cleft. These diffuse across the cleft and transmit the signal to the postsynaptic membrane of the muscle fiber, leading to a post-synaptic potential responsible for muscle contraction. GO:0098520 cellular_component 2013-10-14T12:02:51Z