General physiology: positive feedback in labour: 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.

Try it

Physiology · General physiology: positive feedback in labour

Sample item

During labour the fetal head stretches the cervix, which increases oxytocin release, which strengthens uterine contractions and pushes the head harder against the cervix. This cycle ends only with delivery. How is this control loop best classified?

AOpen-loop control with no sensory input to the effectorBPositive feedback, which amplifies the stimulus until an external event terminates itCFeedforward control, which anticipates a disturbance before it occursDNegative feedback, which restores a fixed set point

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

The answer and the reasoning

B. Positive feedback, which amplifies the stimulus until an external event terminates it

In positive feedback the response intensifies the original stimulus, so the system moves away from its starting state until something outside the loop (here, expulsion of the fetus) ends it. The cervical stretch to oxytocin pathway is the Ferguson reflex. Other examples include the LH surge and the rising phase of the action potential.

Option by option

A. Open-loop control with no sensory input to the effector
The loop has a sensory afferent (cervical stretch receptors), so it is a closed loop.
B. Positive feedback, which amplifies the stimulus until an external event terminates it (correct)
Correct. Each contraction increases cervical stretch and further oxytocin release until delivery stops the stimulus.
C. Feedforward control, which anticipates a disturbance before it occurs
Feedforward control acts in anticipation of a change, whereas here the response follows and amplifies the stimulus.
D. Negative feedback, which restores a fixed set point
Negative feedback would damp the contractions as the cervix stretched, which does not happen.

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 B, Positive feedback, which amplifies the stimulus until an external event terminates it. In positive feedback the response intensifies the original stimulus, so the system moves away from its starting state until something outside the loop (here, expulsion of the fetus) ends it.

Why is "Open-loop control with no sensory input to the effector" not the answer?

The loop has a sensory afferent (cervical stretch receptors), so it is a closed loop.

Why is "Feedforward control, which anticipates a disturbance before it occurs" not the answer?

Feedforward control acts in anticipation of a change, whereas here the response follows and amplifies the stimulus.

Why is "Negative feedback, which restores a fixed set point" not the answer?

Negative feedback would damp the contractions as the cervix stretched, which does not happen.

What concept does this question test?

It tests General physiology: positive feedback in labour in Physiology. The cervical stretch to oxytocin pathway is the Ferguson reflex. Other examples include the LH surge and the rising phase of the action potential.

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: positive feedback in labour?

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.