Neuroanatomy: abducens nucleus: practice question

A Anatomy question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Anatomy · Neuroanatomy: abducens nucleus

Sample item

A pontine infarct produces a right lower motor neuron facial palsy and inability to move both eyes to the right. Which structure beneath the floor of the fourth ventricle is damaged?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Right abducens nucleus

Facial nerve fibres loop around the abducens nucleus at the facial colliculus. A lesion there damages the facial fibres and the abducens nucleus, including the interneurons that project across to the opposite oculomotor nucleus, so neither eye can look to that side.

Option by option

  • A. Right medial longitudinal fasciculus

    A medial longitudinal fasciculus lesion causes internuclear ophthalmoplegia, with failed adduction of one eye and no facial palsy.

  • B. Right trochlear nucleus

    The trochlear nucleus lies in the midbrain and its lesion affects the superior oblique muscle.

  • C. Right abducens nucleus (correct)

    Correct. Facial palsy with a horizontal gaze palsy to the same side localises to the abducens nucleus.

  • D. Right vestibular nuclei

    Vestibular nuclei damage causes vertigo and nystagmus rather than gaze palsy with facial palsy.

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.

More Anatomy questions

Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is C, Right abducens nucleus. Facial nerve fibres loop around the abducens nucleus at the facial colliculus.

Why is "Right medial longitudinal fasciculus" not the answer?

A medial longitudinal fasciculus lesion causes internuclear ophthalmoplegia, with failed adduction of one eye and no facial palsy.

Why is "Right trochlear nucleus" not the answer?

The trochlear nucleus lies in the midbrain and its lesion affects the superior oblique muscle.

Why is "Right vestibular nuclei" not the answer?

Vestibular nuclei damage causes vertigo and nystagmus rather than gaze palsy with facial palsy.

What concept does this question test?

It tests Neuroanatomy: abducens nucleus in Anatomy. A lesion there damages the facial fibres and the abducens nucleus, including the interneurons that project across to the opposite oculomotor nucleus, so neither eye can look to that side.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Neuroanatomy: abducens nucleus?

Learn every nerve by its route, its muscles and what a lesion looks like at the bedside. That one habit answers a large share of questions. Then use the flashcards and the other Anatomy questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.