Neurophysiology: basal ganglia: 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: basal ganglia

Sample item

Loss of dopaminergic neurons of the substantia nigra pars compacta causes bradykinesia. Which change in the basal ganglia circuit explains this?

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

The answer and the reasoning

D. Reduced direct pathway activity and increased indirect pathway activity, so the thalamus is over-inhibited

Dopamine excites the direct pathway through D1 receptors and inhibits the indirect pathway through D2 receptors. Its loss reduces direct pathway facilitation and increases indirect pathway activity, so the globus pallidus interna over-inhibits the thalamus and cortical motor drive falls.

Option by option

  • A. Increased direct pathway activity and decreased indirect pathway activity

    This pattern would produce excess movement, not bradykinesia.

  • B. Reduced inhibition of the thalamus by the globus pallidus interna

    GPi inhibition of the thalamus increases, not decreases, in Parkinson disease.

  • C. Loss of subthalamic nucleus activity with excess thalamic drive

    Subthalamic activity increases in Parkinson disease; its loss causes hemiballismus.

  • D. Reduced direct pathway activity and increased indirect pathway activity, so the thalamus is over-inhibited (correct)

    Correct. Net thalamic inhibition rises, giving hypokinesia.

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 D, Reduced direct pathway activity and increased indirect pathway activity, so the thalamus is over-inhibited. Dopamine excites the direct pathway through D1 receptors and inhibits the indirect pathway through D2 receptors.

Why is "Increased direct pathway activity and decreased indirect pathway acti…" not the answer?

This pattern would produce excess movement, not bradykinesia.

Why is "Reduced inhibition of the thalamus by the globus pallidus interna" not the answer?

GPi inhibition of the thalamus increases, not decreases, in Parkinson disease.

Why is "Loss of subthalamic nucleus activity with excess thalamic drive" not the answer?

Subthalamic activity increases in Parkinson disease; its loss causes hemiballismus.

What concept does this question test?

It tests Neurophysiology: basal ganglia in Physiology. Its loss reduces direct pathway facilitation and increases indirect pathway activity, so the globus pallidus interna over-inhibits the thalamus and cortical motor drive falls.

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 Neurophysiology: basal ganglia?

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.