The Human Brain : From Neurone to Nervous System
MOTOR CONTROL: The Cortico-Spinal (Pyramidal) Tract and Motor Cortex
- The Cortico-Spinal (Pyramidal) Pathway is the major pathway connecting the Motor Cortex to the musculature of the opposite side of the body. It is the executive pathway that controls movements (rather than individual muscles) of the opposite site of the body.
- Cortico-spinal neurones in the primary motor cortex (the pre-central gyrus) have axons that terminate in the contralateral ventral horn of the spinal cord.
The majority of the cortico-spinal axons cross the midline in the decussation of the pyramids within the medulla; as a consequence the motor cortex of one hemisphere controls the movements of the opposite side of the body. Sometimes the term 'upper motoneurone' is used to describe this function.
The motor cortex contains a somatotopic map of the range of movements of the opposite side of the body; each area within the map can induce contractions of relevant muscle groups rather than individual muscles. This is the executive pathway in the control of voluntary movements.
For movements where the greatest precision is required, the area of motor cortex that controls that movement is markedly increased. The prehensile thumb of primates has an especially large repertoire of movements, and has a very large area of motor cortex devoted to the control its muscles.
Key Words: Corticospinal Tract, Motor Cortex, Internal Capsule, Decussation of the Pyramids; Somatotopic Maps of the Musculature, Motor Homunculus.