18.7: Direct Motor Pathways
The direct motor pathways, also known as the pyramidal tracts, are a group of neural pathways that originate in the brain and descend through the spinal cord. They control the voluntary movement of the body. There are two major direct motor pathways: the corticospinal and the corticobulbar tracts.
The corticospinal tract is responsible for the voluntary movement of the limbs and trunk. It originates in the cerebral cortex of the brain and descends through the cerebrum's internal capsule and the midbrain's cerebral peduncle. From there, it enters the spinal cord and travels down the length of the spinal column. As it descends, the corticospinal tract gives off branches to innervate different spinal cord levels. Most fibers end in the ventral horn, where they synapse with lower motor neurons that innervate the skeletal muscles.
The corticobulbar tract is responsible for the voluntary control of the face, tongue, and throat muscles. It originates in the cerebral cortex and descends through the internal capsule, like the corticospinal tract. However, instead of traveling down the spinal cord, it terminates in the brainstem, synapses with cranial nerves controlling the facial and head muscles.
Both the corticospinal and corticobulbar tracts are composed of upper motor neurons, which originate in the cerebral cortex, and lower motor neurons, which innervate the muscles.
