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Physiology · Neurophysiology and special senses: subthalamic nucleus
Sample itemA 70-year-old man has sudden violent flinging movements of the right arm and leg after a small lacunar infarct. Which structure is most likely involved?
Original practice item, not a recalled exam question. Nothing here is recorded.
The answer and the reasoning
B. Left subthalamic nucleus
Hemiballismus follows a lesion of the subthalamic nucleus, which normally excites the output of the basal ganglia to restrain movement. The basal ganglia act on the opposite side of the body, so right-sided movements indicate a left lesion.
Option by option
A. Left substantia nigra pars compacta
Loss of the substantia nigra pars compacta causes a hypokinetic parkinsonian state.
B. Left subthalamic nucleus (correct)
Correct. A left subthalamic lesion causes contralateral right-sided hemiballismus.
C. Left caudate nucleus
Caudate damage is associated with chorea, not violent flinging movements.
D. Right subthalamic nucleus
A right subthalamic lesion would cause movements on the left.
Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.
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