In a supranuclear CN XII palsy, the tongue deviates toward which side?

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Study for the NBEO Ocular Anatomy Posterior Segment and Cranial Nerves Test. Prepare using flashcards and multiple choice questions. Get ready for your exam with hints and explanations for each question!

Multiple Choice

In a supranuclear CN XII palsy, the tongue deviates toward which side?

Explanation:
In supranuclear CN XII palsy the tongue shows weakness on the side opposite the brain lesion because the corticobulbar input to the hypoglossal nucleus is largely contralateral. With a unilateral upper motor neuron lesion, the muscles on the opposite side lose input and become weak. When the tongue is protruded, the intact, stronger side pushes the tongue toward the weaker side, so the tongue deviates away from the lesion. This differs from a lower motor neuron CN XII palsy, where the deviation would be toward the side of the lesion.

In supranuclear CN XII palsy the tongue shows weakness on the side opposite the brain lesion because the corticobulbar input to the hypoglossal nucleus is largely contralateral. With a unilateral upper motor neuron lesion, the muscles on the opposite side lose input and become weak. When the tongue is protruded, the intact, stronger side pushes the tongue toward the weaker side, so the tongue deviates away from the lesion. This differs from a lower motor neuron CN XII palsy, where the deviation would be toward the side of the lesion.

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