DESCENDING TRACTS

Question 1

where is the primary motor cortex and how is it arranged?

Answer 1

pre central gyrus
motor homunculus

Question 2

What are some of the descending tracts?

Answer 2

CORTICOSPINAL TRACT (lateral and ventral)
rubrospinal tract
tectospinal tract
reticulospinal tract
vestibulospinal tract

Question 3

Key function of the corticospinal tract

Answer 3

fine motor skills

Question 4

pathway of the corticospinal tract

Answer 4

fibres from cortex –> decsends down the internal capsule –> midbrain –> pons –> medulla oblongata –> pyramids –> 85% fibres decussate at the pyramids –> crossed fibres form the lateral CST –> descends down to the Cervical and lumbar segments depending on the homunculus (LL–> lumbar segments, UL –> Cervical segments) –> Synapse with the motor neurone at the anterior grey horn.

15% fibres that did not decussate –> form the anterior CST –> descends down to the cervical and lumbar segments (fibres from UL and LL respectively) –> decussate at anterior grey commissure –> contralateral anterior grey horn –> synapse with the motor neurone.

Question 5

clinical relevance of Internal capsule

Answer 5

CVA of internal capsule –> lack of descending CST –> spastic paralysis with hyeprflexion of UL

Question 6

What is Decorticate posturing and what causes it?

Answer 6

loss of CST function –> spastic paralysis with hyperflexion of the UL
caused by CVA of internal capsule