Extrapyramidal tracts
- Vestibulospinal tract
- The lateral vestibulospinal tract controls muscle tone in leg extensors (anti-gravity muscles), which help maintain upright posture.
- The medial vestibulospinal tract innervates neck musculature and facilitates muscle tone and head movements.
- Over-extension is prevented by red nucleus
- Ponto reticulospinal tract
- Originate from pons
- Assist in posture maintaining, like vestibulospinal tract
- Rubrospinal pathway
- Assist corticospinal tract to control flexor muscles
- Originate from red nucleus
- Medullary Reticulospinal Tract
- Similar as above
- Red nucleus is in midbrain, at the level of the oculomotor nerve nucleus
- Damage above the red nucleus (eg, cerebral hemisphere, internal capsule) typically results in decorticate (flexor) posturing due to loss of descending inhibition of the red nucleus and subsequent hyperactivity of upper limb flexors.
- Damage below the red nucleus (eg, pons) or to the nucleus itself (eg, midbrain) often causes decerebrate (extensor) posturing due to loss of descending excitation to the upper limb flexors (via the rubrospinal tract) and extensor predominance (due to unopposed vestibulospinal tract output).
Mnemonic
- When it's decorticate posturing, lesion is in up, thus hands and arms lifting up
- When it's decerebrate posturing, lesion is in down, thus hands and arms dropping down