Neurophysiology: cerebrospinal fluid composition: practice question

A Physiology 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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Physiology · Neurophysiology: cerebrospinal fluid composition

Sample item

Compared with plasma, normal cerebrospinal fluid has which composition?

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

The answer and the reasoning

B. Higher chloride, lower potassium and very low protein

The choroid plexus secretes CSF actively, producing a fluid with more chloride and less potassium, glucose and protein than plasma. Protein is only about 20 to 40 mg/dL.

Option by option

  • A. Higher glucose and high protein

    CSF glucose is about 60 percent of plasma levels, and protein is much lower.

  • B. Higher chloride, lower potassium and very low protein (correct)

    Correct. CSF has a chloride-rich, potassium-poor, protein-poor profile.

  • C. Higher potassium, lower chloride and a very low protein

    This reverses the chloride and potassium differences.

  • D. Identical composition to plasma

    CSF is not an ultrafiltrate of plasma; it is actively secreted.

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 Physiology question

What is the answer to this Physiology question?

The best answer is B, Higher chloride, lower potassium and very low protein. The choroid plexus secretes CSF actively, producing a fluid with more chloride and less potassium, glucose and protein than plasma.

Why is "Higher glucose and high protein" not the answer?

CSF glucose is about 60 percent of plasma levels, and protein is much lower.

Why is "Higher potassium, lower chloride and a very low protein" not the answer?

This reverses the chloride and potassium differences.

Why is "Identical composition to plasma" not the answer?

CSF is not an ultrafiltrate of plasma; it is actively secreted.

What concept does this question test?

It tests Neurophysiology: cerebrospinal fluid composition in Physiology. Protein is only about 20 to 40 mg/dL.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Neurophysiology: cerebrospinal fluid composition?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.