Neuroanatomy: blood-CSF barrier: 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: blood-CSF barrier

Sample item

The capillaries of the choroid plexus are fenestrated, yet the CSF it produces differs in composition from plasma. Which structure forms the blood-CSF barrier at this site?

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

The answer and the reasoning

D. Tight junctions of choroid epithelial cells

Choroid plexus capillaries are leaky, so the barrier is formed by tight junctions between the modified ependymal epithelial cells covering the plexus. These cells actively secrete CSF and control what enters it.

Option by option

  • A. Ependymal cells lining the ventricular wall

    Ordinary ependymal cells away from the plexus lack tight junctions and do not form this barrier.

  • B. Basement membrane of the choroidal capillaries

    The basement membrane is a loose supporting layer and does not restrict solutes.

  • C. Astrocyte foot processes around the capillaries

    Astrocyte foot processes support the blood-brain barrier elsewhere but do not surround fenestrated plexus capillaries.

  • D. Tight junctions of choroid epithelial cells (correct)

    Correct. The epithelium of the plexus is sealed by tight junctions, which is the barrier at this site.

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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Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is D, Tight junctions of choroid epithelial cells. Choroid plexus capillaries are leaky, so the barrier is formed by tight junctions between the modified ependymal epithelial cells covering the plexus.

Why is "Ependymal cells lining the ventricular wall" not the answer?

Ordinary ependymal cells away from the plexus lack tight junctions and do not form this barrier.

Why is "Basement membrane of the choroidal capillaries" not the answer?

The basement membrane is a loose supporting layer and does not restrict solutes.

Why is "Astrocyte foot processes around the capillaries" not the answer?

Astrocyte foot processes support the blood-brain barrier elsewhere but do not surround fenestrated plexus capillaries.

What concept does this question test?

It tests Neuroanatomy: blood-CSF barrier in Anatomy. These cells actively secrete CSF and control what enters it.

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: blood-CSF barrier?

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.