Key POINTS

1. The central nervous system structures controlling movement have a hierarchical organization.

2. The spinal cord is the most caudal and simplest level of the movement control hierarchy.

3. Brainstem upper motor neuron pathways are the source of all descending motor system input to the spinal cord, except for one other major pathway.

4. Medial and lateral descending brainstem motor pathways respectively control proximal muscles of posture and more distal muscles of skilled movement.

5. The reticulospinal and vestibulospinal tracts are medial brainstem motor pathways important for keeping the body upright against the pull of gravity.

6. The rubrospinal tract is a lateral brainstem motor pathway that can control distal limb musculature associated with skilled movement.

7. The corticospinal (pyramidal) tract is a direct projection from cerebral cortex to spinal cord responsible for the most skilled voluntary movements of mammals.

8. The corticospinal tract has a massive lateral component controlling the distal musculature and a minor medial component controlling the axial and proximal musculature.

9. The motor cortices of the frontal lobe, the highest level of the motor control hierarchy, consist of three different functional regions.

10. Corticospinal tract co-activation of both alpha (α) and gamma (γ) lower motor neurons may help with small automatic corrections of voluntary movements.

11. The motor system shares some organizational principles with sensory systems.

12. The basal ganglia and cerebellum modulate the activity of motor system components for the respective selection and adjustment of movement.