Tract Site Of Origin Site Of Decussation Levels Of

Site of Origin

Tract

Site of decussation Levels of Termination (crossing over)

Function

Other Info

Lateral Motor Systems Primary motor cortex - B4 (33%) premotor cortex - B6 (33%), somatosensory cortex Lateral Corticospinal Tract B3,1,2 (33%)

Red nucleus, magnocellular division

Rubrospinal Tract

Pyramidal decussation at Entire Cord Movement of Contralateral the cervicomedullary predominately at cervical Limbs - rapid, dextrous mvmt junction (medulla/SC) and lubosacral at individual digits or joints (90% of fibers cross) enlargements (voluntary, skilled mvmt) Lesion ABOVE pyramidal dec= contralateral weakness/Lesion BELOW=Ipsilateral weakness

Ventral tegmental decussation -midbrain

Cervical cord

red nuc receives input from cerebral cortex and cerebellar nuclei

The fibers that do not cross at the medullary pyramids (10%) descend ipsilaterally and are the anterior cortiocospinal tract; Lesions = dramatic deficits

-Axons descend thru the corona radiata, post limb of internal capsule, middle of cerebral peduncle (crus cerebri), and medullary pyramids (anterior/medial thru the brainstem) inhibits Extensor mm/ excites Flexor mm Movement of contralateral clinical importance uncertain - may take over limbs (function uncertain in functions after cotricospinal injury humans) excites motor Or, may play role in flexor neurons innervating flexor (decorticate) posturing of upper extremeties mm in proximal limb seen in lesions above red nucleus = rubrospinal tract spared Descends in the lateral brainstem and the lateral funiculus of the SC then projects to LMNs that are more medial = proximal limb

Medial Motor Systems Primary motor cortex and…..

Tract runs to terminal cervical and upper LMN ipsilaterally and also thoracic cord crosses thru the ventral white commissure to the contralateral side at the same level. = bilateral effects

lateral vestibular nucleus (pons)

none - projects ipsilaterally only

Anterior cortiospinal tract

entire cord

Lateral Vestibulospinal Tract

medial vestibular nucleus none (rostral medulla)

cervical and uppper thoracic cord

Medial Vestibulospinal Tract

Pontine (MRST) and medullary reticular formation (LRST) Reticulospinal tracts

Tectospinal tract

LRST: crossed and uncrossed : inhibits extensors

LRST: axons descend bilaterally thru lateral fasciculus to all levels

Control of bilateral axial and girdle muscles

This tract is made up of fibers from the lateral corticospinal tract (the 10%) that did not cross at the meduallary pyramids. They descends in the anterior funiculus of the SC. Unilateral lesions = no obvious deficits

maintain upright posture and activity of pathway modified by input to the balance by exciting extensors lateral vest nuc from the cerebellum and of mainly the legs from sensory receptors in the inner ear via CN VIII Lesion of CNVIII or vestibular nuc = stumbling and/or falling toward the side of the lesion 1.) adjusts head position in axons DESCEND project bilaterally - ip si and response to change in posture contra to the ventral horn of the cervical SC 2.) coordinates eye mvmts and to LMNs associated with the spinal with each other 3.) accessory n. coordinates eye mvmts to Also axons ASCEND in the MLF (medial compensate for head mvmts long fasciculus) to the nuclei of CN III, IV and (VOR) VI - path coordinates eye mvmt with each other and with head mvmt

maintain upright posture thru LRST: Lateral (Medullary) reticulospinal tract voluntary and reflexive mvmts -"mellow" - done by inhibiting LRST or MRST: exciting MRST motor nuerons Medial (Pontine) Reticulospinal tract that inn axial mm -"pumped up" MRST: no crossing: MRST: descend 2nd function: excites extensors ipsilaterally in anterior convey autonomic info from higher levels fasciculus to all levels about resp, circ., sweating, shivering, pupil dilation, sphincter mm in GI and urinary tracts Ascending fibers of LRST Superior Colliculus dorsal tegmental cervical cord coordination of head and eye very uncommon to nuclei have a- lesion project to thalamic role inhere arousal and (corticotectal fibers arise decussation, in the contralateral (CN XI nuc- mvmt (uncertain in humans) -Parinaud's Syndrome/dorsal midbrain sleep in the Retina, visual cortex midbrain sternocleidomasteoid m) syndrome one possibility, usually seen in and inferiorparietal lobes) peds