Neuroanatomy USMLE Step 1 Practice Question
A 67-year-old man with hypertension presents with acute-onset right facial droop and arm weakness. Vital signs: BP 158/92, HR 88, RR 16, Temp 37°C, SpO2 98%. Neurologic exam reveals right arm weakness (2/5) greater than right leg weakness (4/5); facial droop present. MRI confirms acute left middle cerebral artery stroke involving the motor cortex. Serum glucose 118 mg/dL. No aphasia or visual field deficits noted. Which anatomical organization of the motor cortex best explains this selective weakness pattern?
Answer choices
- AThe primary motor cortex is located in the postcentral gyrus
- BThe corticospinal tract decussates at the level of the midbrain
- CThe motor cortex lacks innervation to muscles of facial expression
- DThe motor cortex has greater cortical representation for upper extremities than lower extremitiesCorrect answer
- ELower extremity motor control is exclusively ipsilateral
- FThe motor cortex receives dual blood supply from both the anterior and middle cerebral arteries, protecting lower extremity function
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