 Skeletal muscles are directly controlled by motor neurons located in the spinal cord or, in a few cases, the brainstem.These motor neurons send their axons through motor nerves, from which they emerge to connect to muscle fibers at a special type of synapse called the neuromuscular junction.When a motor neuron generates an action potential, it travels rapidly along the nerve until it reaches the neuromuscular junction, where it initiates an electrochemical process that causes acetylcholine to be released into the space between the presynaptic terminal and the muscle fiber.