Upper motor neurone axon: corona radiata, posterior limb of internal capsule, crus cerebri, basis pontis and medullary pyramid
First-order neurone / UMN · uncrossed UMN
The single corticospinal axon leaves the cortex through the corona radiata, is packed into the posterior limb of the internal capsule (corticobulbar fibres lie in the genu), descends in the middle three-fifths of the crus cerebri, is broken into bundles by the pontine nuclei, and regroups as the medullary pyramid on the ventral surface of the medulla. It has not yet crossed.
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
Detail
- Internal capsule
- Posterior limb (corticobulbar in genu; arm fibres anterior to leg fibres)
- Midbrain
- Middle three-fifths of the crus cerebri
- Medulla
- Pyramid, ventral to the medial lemniscus
- Blood supply
- Lenticulostriate branches of the middle cerebral artery (capsule); anterior spinal artery (pyramid)
When it goes wrong
Lacunar infarct of the posterior limb of the internal capsule (lenticulostriate artery, hypertension)
Pure motor hemiparesis: dense contralateral weakness of face, arm and leg equally, with no sensory, visual or cortical signs
Medial medullary syndrome (anterior spinal or paramedian vertebral artery)
Contralateral hemiparesis sparing the face (pyramid), contralateral loss of vibration and proprioception (medial lemniscus) and ipsilateral tongue weakness with deviation towards the lesion (hypoglossal nerve)
Practise this structure
1 question in the bank tagged Upper Motor Neurone.