Final answer:
Skeletal muscles are innervated by axon terminals of motor neurons from the spinal cord or brainstem, forming motor units. These muscles facilitate both voluntary and involuntary movements through signals transmitted by the neurons.
Step-by-step explanation:
The skeletal muscles of the body are innervated by the axon terminals of motor neurons. Each skeletal muscle fiber is innervated by a single motor neuron, and collectively, the muscle fibers innervated by one motor neuron make up a motor unit. These motor neurons originate in the spinal cord and, for the muscles of the face, head, and neck, from the brainstem. They send signals to the muscle fibers to contract through their axons, which can extend long distances from the spinal cord to the target muscle.
Additionally, the skeletal muscles are involved in both voluntary movement, such as choosing to move an arm, as well as involuntary reflexes, such as withdrawing a hand from a hot surface. The only way skeletal muscles can contract is by receiving a signal from the nervous system, distinguishing them from cardiac and smooth muscles.