Somatic Motor Pathways

Nerves that extend out of the brain stem and spinal cord are called lower motor neurons (LMNs). These nerves innervate skeletal muscles of the face and head through cranial nerves, and skeletal muscles of the limb and trunk through spinal nerves.
Somatic motor pathways provide the input into lower motor neurons and are divided into four distinct circuits.
Local circuit neurons are located close to LMNs in the brain stem and spinal cord.
Upper motor neurons (UMNs): input to both lower circuit neurons and LMNs.
Basal nuclei neurons: assist movement by providing input to UMNs.
Cerebellar neurons: assist movement via control of activity of UMNs.