[OT 104] Lec. 4: White Matter - Descending Motor Tracts & Pathways

First order

• upper motor neurons in the cerebral cortex or brain stem

Second order

• interneurons in the spinal cord

Third order

• lower motor neurons that innervate skeletal/visceral ms

Lateral Corticospinal Tract (LCST)

Function: fine motor (distal musculature)

Location: lateral column

Origin: motor and premotor cortex

Decussation: medullary pyramids

Ending: anterior horn cells (interneurons and lower motor neurons)

e.g. writing, buttoning

Anterior Corticospinal Tract (ACST)

Function: gross and postural motor, proximal and axial musculature

Location: anterior column

Origin: motor and premotor cortex

Decussation: uncrossed until after descending to relevant segments

Ending: anterior horn cells

e.g. walking, jogging

Vestibulospinal tract (VST)

Function: postural reflexes, control of antigravity (extensor) ms

Location: anterior column

VST: Medial

Origin: medial vestibular nucleus in the brain stem

Course: descends bilaterally in the medial longitudinal fasciculus

Ending: anterior horn cell interneurons (at laminae 7 and 9) and LMNs (extensors)

VST: Lateral

Origin: lateral vestibular nucleus in the brain stem

Course: descends ipsilaterally in the anterior funiculus of the same side of SC

Ending: anterior horn cells interneurons (laminae 7 and 9) and LMNs (extensors)

e.g. walking on a balance

Rubrospinal tract (RuST)

Function: controls distal flexor ms and tone, inhibits distal extensor ms, modulates reflex activity

Location: lateral column

Origin: red nucleus in the brainstem

Decussation: immediately decussates

Ending: dorsal and anterior horn interneurons

e.g. wrist flexion, extensor posturing

Reticulospinal tract (ReST)

Function: maintains posture, autonomic functions, locomotion, reflexes

Location: ventral and lateral columns

Origin: brainstem reticular formation

Ending: ventral and lateral horn interneurons

e.g. breathing, heart beat

Tectospinal tract (TeST)

Function: reflex head turning to visual or auditory stimuli

Location: ventral column

Origin: midbrain (superior colliculi)

Decussation: decussates after origin

Ending: ventral horn neurons

e.g. head turning

Descending Autonomic Tract (DAT)

Function: modulates autonomic functions

Location: lateral column

Origin: hypothalamus, brainstem nuclei

Ending: preganglionic autonomic neurons

Medial Longitudinal Fasciculus (MLF)

Function: coordination of head and eye movements

Location: ventral column

Origin: vestibular nuclei

Ending: cervical gray interneurons