- With the noted bilateral exceptions, lesion of the pyramidal tract above
the decussation results in spastic paralysis, loss of fine movements, and
hyperreflexia on the contralateral side. - Lesion of the corticospinal tract in the cord results in ipsilateral deficits.
The Extrapyramidal (Basal Ganglia) System
- The basal ganglia (caudate, putamen, globus pallidus) and associated
nuclei (e.g., substantia nigra) do not project directly to medullary or
spinal lower motor neurons, but to the motor cortex. - The system controls coarse, stereotyped movements. Lesions result in
altered muscle tone (usually rigidity), paucity of movement, and the
appearance of rhythmic tremors and writhing or jerky movements.
Reticular Pathways
- Nuclei of the reticular system send ascending projections to the hypo-
thalamus and thalamus as well as descending projections to the motor
nuclei of cranial nerves, and the intermediate gray of the spinal cord. - The reticular formation has reciprocal connections with most other areas
of the CNS and produces both faciliatory and inhibitory effects on motor
systems, receptors, and sensory conduction pathways.
42 Anatomy, Histology, and Cell Biology