General physiology: osmoreceptors and the lamina terminalis: 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 · General physiology: osmoreceptors and the lamina terminalis

Sample item

Neurons of the organum vasculosum of the lamina terminalis respond to changes in plasma osmolality of only 1 to 2 percent and drive thirst and ADH release. What allows them to sense plasma directly?

AThey are embedded in the posterior pituitary beside the venous sinusesBThey are driven mainly by carotid baroreceptor afferentsCThey detect intracellular potassium rather than extracellular tonicityDThey lie in a circumventricular organ whose fenestrated capillaries lack a blood-brain barrier

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

The answer and the reasoning

D. They lie in a circumventricular organ whose fenestrated capillaries lack a blood-brain barrier

The OVLT and subfornical organ are circumventricular organs with leaky capillaries, so their neurons are exposed to circulating solutes and shrink when plasma tonicity rises. This triggers thirst and signals supraoptic and paraventricular neurons to release ADH.

Option by option

A. They are embedded in the posterior pituitary beside the venous sinuses
The posterior pituitary stores and releases ADH but does not contain the osmoreceptors.
B. They are driven mainly by carotid baroreceptor afferents
Baroreceptor input mediates volume-related stimuli; osmotic sensing is direct and more sensitive.
C. They detect intracellular potassium rather than extracellular tonicity
These neurons respond to extracellular tonicity through cell shrinkage, not intracellular potassium.
D. They lie in a circumventricular organ whose fenestrated capillaries lack a blood-brain barrier (correct)
Correct. Absence of a blood-brain barrier exposes these neurons to plasma.

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 Physiology question

What is the answer to this Physiology question?

The best answer is D, They lie in a circumventricular organ whose fenestrated capillaries lack a blood-brain barrier. The OVLT and subfornical organ are circumventricular organs with leaky capillaries, so their neurons are exposed to circulating solutes and shrink when plasma tonicity rises.

Why is "They are embedded in the posterior pituitary beside the venous sinuses" not the answer?

The posterior pituitary stores and releases ADH but does not contain the osmoreceptors.

Why is "They are driven mainly by carotid baroreceptor afferents" not the answer?

Baroreceptor input mediates volume-related stimuli; osmotic sensing is direct and more sensitive.

Why is "They detect intracellular potassium rather than extracellular tonicity" not the answer?

These neurons respond to extracellular tonicity through cell shrinkage, not intracellular potassium.

What concept does this question test?

It tests General physiology: osmoreceptors and the lamina terminalis in Physiology. This triggers thirst and signals supraoptic and paraventricular neurons to release ADH.

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 General physiology: osmoreceptors and the lamina terminalis?

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.