Motor Nerves

MOTOR NERVES, transmit irritation from the central nervous system to muscles. M. n. represent the axons of multipolar motor cells, together with which they form a functional unit—the motor neuron. The initial part of the axon from the nucleus to the point of exit from the skull or spinal canal is called the root, and further (toward the periphery)—the motor nerve. In the cervical and lumbosacral regions of the spinal cord, M. n. differentiate from plexuses. Impulses for M. n. to striated voluntary muscles travel along corticonuclear and pyramidal/extrapyramidal pathways, while to the heart muscles and other internal organs—along extrapyramidal pathways. M. n. of the heart and smooth muscles of blood vessels, the eye, hair, bronchi, and internal organs belong to the autonomic nervous system. They begin from ganglion cells of special motor nuclei of the brain and spinal cord, with the axons of cells from the central nervous system ending in sympathetic ganglia (preganglionic fibers). From the ganglion cells of the latter, axons extend directly to the effector organ (postganglionic fibers). Preganglionic motor fibers of the autonomic system are myelinated, postganglionic are non-myelinated, gray. The anatomical-histological structure—see Autonomic nervous system. M. n., which are the physiological continuation of the pyramidal pathways, are covered with a myelin sheath throughout their length—myelinated, white fibers (see also Nerves).