The connection may be with other neurons, with specialized glands, or with muscles. Figure 13.25 depicts the formation of a neuromuscular synapse. Formation of the neuromuscular junction requires reciprocal interactions between the neuron and the muscle . Axon of motor neuron releases agrin at the junction with the muscle. ACh receptors cluster at the junction and synthesis of receptors occurs.
Electrical activity reduces receptor synthesis elsewhere.
Note that during development, multiple neurons will contact a single muscle cell, but only one contact is maintained. When one motor neuron becomes active, it suppresses the formation of other synapses. Thus, the correct wiring of neuromuscular junctions is activity dependent. Motor neuron death is a normal part of development in the chick spinal cord.