extrapyramidal tracts, the uncrossed tracts of motor nerves from the brain to the anterior horns of the spinal cord, except the crossed fibers of the pyramidal tracts. Within the brain, extrapyramidal pathways comprise various relays of motoneurons between motor areas of the cerebral cortex, the basal nuclei, the thalamus, the cerebellum, and the brainstem. The extrapyramidal pathways are functional rather than anatomical units, comprising the nuclei and the fibers and excluding the pyramidal tracts. They especially control and coordinate the postural, static, supporting, and locomotor mechanisms and cause contractions of muscle groups sequentially or simultaneously. The extrapyramidal pathways include the corpus striatum, the subthalamic nucleus, the substantia nigra, and the red nucleus, together with their interconnections with the reticular formation, the cerebellum, and the cerebrum. Compare pyramidal tract.
