Anterior corticospinal tract (uncrossed 10-15%)
Second-order tract · detail · uncrossed 10-15% axial
The uncrossed minority bypasses the pyramidal decussation and descends in the anterior funiculus beside the anterior median fissure, crossing in the anterior white commissure at its own segment to end mainly on medial anterior horn cells for axial and proximal girdle muscles. Many of these muscles receive cortical input from both hemispheres.
Traced from the start
- Primary motor cortex (precentral gyrus, Brodmann area 4)
- Upper motor neurone axon: corona radiata, posterior limb of internal capsule, crus cerebri, basis pontis and medullary pyramid
- Anterior corticospinal tract (uncrossed 10-15%)
Detail
- Position
- Anterior funiculus
- Crosses
- Anterior white commissure at its segmental level
- Supplies
- Axial and proximal muscles (bilateral cortical input)
When it goes wrong
Unilateral UMN lesion (capsular stroke)
Trunk and neck muscles are largely spared because they keep bilateral corticospinal input, so distal limb weakness dominates the picture
Practise this structure
1 question in the bank tagged Upper Motor Neurone.