Lateral corticospinal tract
Second-order tract · crossed distal limb
The crossed 85 to 90 per cent of pyramidal axons descend in the lateral funiculus, medial to the dorsal spinocerebellar tract, with cervical fibres innermost and sacral fibres outermost, giving off axons at every segment to the anterior horn. Most end on interneurones, but those to the hand muscles are monosynaptic. It is the main pathway for skilled distal movement.
Traced from the start
Detail
- Position
- Lateral funiculus, anterior to the dorsal horn
- Somatotopy
- Cervical fibres medial, sacral fibres lateral
- Supplies
- Ipsilateral anterior horn cells from the contralateral cortex; mainly distal limb muscles
When it goes wrong
Any lesion of the tract (UMN lesion)
Pyramidal pattern weakness (arm extensors and leg flexors weakest), clasp-knife spasticity, hyperreflexia, clonus, extensor plantar response and no wasting
Brown-Sequard hemisection
Ipsilateral UMN weakness below the lesion
Subacute combined degeneration (vitamin B12 deficiency)
Spastic paraparesis with extensor plantars yet absent ankle jerks from the superimposed peripheral neuropathy, together with loss of vibration sense in the feet
Central cord syndrome (hyperextension injury with cervical spondylosis, expanding syrinx)
Weakness of the arms and hands greater than the legs because the medially placed cervical fibres are damaged first
Motor neurone disease (amyotrophic lateral sclerosis)
Mixed UMN and LMN signs in the same limb, such as brisk reflexes in a wasted fasciculating muscle, with no sensory loss and no sphincter or eye movement involvement
Practise this structure
1 question in the bank tagged Upper Motor Neurone.