NBME Neuroscience 2 — Questions and Answers
Question 1: A patient presents with a dilated, non-reactive pupil and ptosis of the right eye with the eye deviated down and out. Which cranial nerve is most likely compressed?
- Cranial nerve IV (trochlear)
- Cranial nerve III (oculomotor) (Correct answer)
- Cranial nerve VI (abducens)
- Cranial nerve II (optic)
Correct answer: Cranial nerve III (oculomotor)
CN III palsy causes ipsilateral ptosis, dilated unreactive pupil (parasympathetic fibers run on outside), and 'down and out' eye deviation due to unopposed SO and LR action.
Question 2: A patient with a cerebellar lesion on the right side is most likely to show deficits on which side of the body?
- Left side only
- Right side only (Correct answer)
- Bilateral equally
- Neither side — cerebellar lesions cause no limb deficits
Correct answer: Right side only
The cerebellum coordinates ipsilateral limb movements because cerebellar pathways cross twice (net ipsilateral), so right cerebellar lesions cause right-sided ataxia.
Question 3: Stimulation of the direct pathway of the basal ganglia results in which of the following?
- Inhibition of the thalamus via increased GPi activity
- Facilitation of movement via disinhibition of the thalamus (Correct answer)
- Increased release of acetylcholine in the striatum
- Suppression of dopamine from the substantia nigra
Correct answer: Facilitation of movement via disinhibition of the thalamus
The direct pathway (striatum→GPi/SNr) inhibits GPi, disinhibiting the thalamus and facilitating cortical activation and movement.
Question 4: A patient is quadriplegic and anarthric but can move his eyes vertically and blink voluntarily. He is fully conscious. Which structure is most likely damaged?
- Bilateral cerebral cortex
- Ventral pons (Correct answer)
- Dorsal pons and midbrain
- Medullary reticular formation
Correct answer: Ventral pons
Locked-in syndrome results from ventral pontine lesions (often basilar artery occlusion) that destroy the corticospinal and corticobulbar tracts while sparing the ARAS and vertical gaze center in the midbrain.
Question 5: A patient presents with inability to close the right eye, drooping of the right corner of the mouth, and loss of taste from the anterior two-thirds of the right tongue. Where is the lesion?
- Right cerebral cortex (UMN lesion)
- Right facial nerve nucleus or nerve (LMN lesion) (Correct answer)
- Left cerebral cortex (UMN lesion)
- Right glossopharyngeal nerve
Correct answer: Right facial nerve nucleus or nerve (LMN lesion)
LMN CN VII palsy causes complete ipsilateral facial paralysis (including forehead) plus taste loss from anterior 2/3 tongue via chorda tympani; UMN lesions spare the forehead.
Question 6: A patient with multiple sclerosis develops left eye adduction failure on attempted right lateral gaze, with nystagmus of the abducting right eye. Which structure is demyelinated?
- Right abducens nucleus
- Left medial longitudinal fasciculus (MLF) (Correct answer)
- Right oculomotor nucleus
- Left abducens nucleus
Correct answer: Left medial longitudinal fasciculus (MLF)
Internuclear ophthalmoplegia (INO) results from MLF demyelination; the ipsilateral (left) eye fails to adduct on contralateral gaze, and the abducting eye shows nystagmus.
Question 7: Damage to Wernicke's area results in which type of aphasia?
- Non-fluent aphasia with good comprehension
- Fluent aphasia with poor comprehension (Correct answer)
- Pure word deafness with intact reading
- Global aphasia with intact repetition
Correct answer: Fluent aphasia with poor comprehension
Wernicke's aphasia (posterior superior temporal gyrus, dominant hemisphere) produces fluent but paraphasic speech with severely impaired comprehension and repetition.
NBME Neuroscience 2
A patient presents with a dilated, non-reactive pupil and ptosis of the right eye with the eye deviated down and out.
Which cranial nerve is most likely compressed?