Neuroanatomy: motor posturing: 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: motor posturing

Sample item

After a pontine haemorrhage a comatose man shows extension and internal rotation of all four limbs with plantar flexion of the feet. At which level of the brainstem is the lesion?

ABoth internal capsules onlyBBetween red nucleus and vestibular nucleiCAbove the red nucleus, at the thalamusDBelow the vestibular nuclei, in the medulla

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

The answer and the reasoning

B. Between red nucleus and vestibular nuclei

A lesion between the red nucleus and the vestibular nuclei removes the flexor influence of the rubrospinal tract while the vestibulospinal and reticulospinal extensor drive is released, producing decerebrate rigidity. If the lesion lies above the red nucleus the rubrospinal tract still works and the arms flex, which is decorticate posturing.

Option by option

A. Both internal capsules only
Isolated internal capsule lesions cause hemiplegia and do not produce this four-limb extension.
B. Between red nucleus and vestibular nuclei (correct)
Correct. Extensor pathways are unopposed once the rubrospinal influence is cut off below the red nucleus.
C. Above the red nucleus, at the thalamus
A lesion above the red nucleus preserves rubrospinal flexion, giving flexed arms and extended legs.
D. Below the vestibular nuclei, in the medulla
A lesion below the vestibular nuclei removes the extensor drive and gives flaccidity with loss of posturing.

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.

Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is B, Between red nucleus and vestibular nuclei. A lesion between the red nucleus and the vestibular nuclei removes the flexor influence of the rubrospinal tract while the vestibulospinal and reticulospinal extensor drive is released, producing decerebrate rigidity.

Why is "Both internal capsules only" not the answer?

Isolated internal capsule lesions cause hemiplegia and do not produce this four-limb extension.

Why is "Above the red nucleus, at the thalamus" not the answer?

A lesion above the red nucleus preserves rubrospinal flexion, giving flexed arms and extended legs.

Why is "Below the vestibular nuclei, in the medulla" not the answer?

A lesion below the vestibular nuclei removes the extensor drive and gives flaccidity with loss of posturing.

What concept does this question test?

It tests Neuroanatomy: motor posturing in Anatomy. If the lesion lies above the red nucleus the rubrospinal tract still works and the arms flex, which is decorticate posturing.

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: motor posturing?

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.