The cerebral peduncles are two thick stalks on the front of the midbrain that carry descending motor fibres from the cerebral cortex down to the brainstem and spinal cord. In strict terms the peduncle includes the tegmentum and substantia nigra, but the name is often used for the crus cerebri, the dense band of white matter on its front surface.
| Location | Anterior surface of the midbrain, diverging upward from the pons toward the cerebral hemispheres, bordering the interpeduncular fossa |
|---|---|
| Parts | |
| Connections |
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| Blood Supply | Posterior cerebral artery perforators; Posterior communicating artery branches; Anterior choroidal artery; Superior cerebellar artery |
Conducts voluntary motor commands from the cortex to the brainstem, spinal cord and pontine nuclei that relay to the cerebellum.
Damage to the crus cerebri causes contralateral hemiparesis, often with ipsilateral third nerve palsy because the oculomotor nerve emerges just medial to it (Weber syndrome). In uncal herniation the opposite peduncle can be pushed against the tentorial edge (Kernohan notch), causing weakness on the same side as the mass, a false localising sign.
Compression of the contralateral cerebral peduncle against the tentorium during herniation, causing hemiparesis on the same side as the brain lesion.
Shrinkage of the peduncle on MRI weeks to months after a large cortical or capsular stroke, reflecting loss of descending motor fibres.
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