A 55-year-old man suffers a stroke affecting the right internal capsule. He develops contralateral (left) upper motor neuron signs including spastic hemiplegia and hyperreflexia. Which specific part of the internal capsule carries the corticospinal (pyramidal) fibres?
- A Anterior limb
- B Posterior limb ✓
- C Genu
- D Sublenticular part
Correct answer: B. Posterior limb
Explanation
The posterior limb of the internal capsule carries the corticospinal (pyramidal) tract fibres, arranged somatotopically with face fibres most anteriorly (near genu), followed by upper limb and then lower limb more posteriorly. Corticobulbar fibres travel through the genu. The anterior limb carries frontopontine fibres and anterior thalamic radiations. The retrolenticular and sublenticular parts carry optic radiations and auditory radiations respectively. A posterior limb infarct causes pure motor hemiplegia contralateral to the lesion.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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