Primary motor cortex (precentral gyrus, Brodmann area 4)
Receptor or cortex · Betz cells UMN
Layer V pyramidal cells of the precentral gyrus, including the giant Betz cells, give rise to roughly half of corticospinal axons; the rest arise from premotor and supplementary motor areas and from the postcentral somatosensory cortex. The motor homunculus places the leg on the medial surface (anterior cerebral artery territory) and the face and arm on the lateral convexity (middle cerebral artery territory).
Detail
- Cell type
- Layer V pyramidal cells (Betz cells are the largest)
- Contribution
- About half of corticospinal fibres from M1; remainder from premotor, supplementary motor and somatosensory cortex
- Blood supply
- Leg area: anterior cerebral artery; face and arm area: middle cerebral artery
When it goes wrong
Middle cerebral artery territory infarct
Contralateral UMN weakness of the face and arm more than the leg, with aphasia (dominant hemisphere) or neglect (non-dominant)
Anterior cerebral artery territory infarct
Contralateral leg weakness more than arm, often with urinary incontinence and abulia
Focal motor (Jacksonian) seizure
Clonic jerking that marches along the homunculus, for example thumb to hand to face, followed by transient Todd's paresis
Practise this structure
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