NEET-PG Physiology Previous Year Questions (2017–2026)

Correct answer: A. Pacinian, Ruffini, free nerve endings

The deep, large, onion-like lamellated corpuscle is a Pacinian corpuscle (rapidly adapting, senses deep pressure and high-frequency vibration). The spindle-shaped ending among dermal collagen is a Ruffini ending (slowly adapting, senses skin stretch). The bare terminals climbing into the epidermis are free nerve endings (pain, temperature, crude touch). So the correct sequence is Pacinian, Ruffini, free nerve endings.

Incorrect Options:

• B. Ruffini, Pacinian, Merkel: reverses the first two and adds Merkel; the deep lamellated body is Pacinian, not Ruffini.
  
  Ruffini, Pacinian, Merkel.
• C. Meissner, Pacinian, Ruffini: Meissner corpuscles sit in dermal papillae for fine touch, not deep in the dermis.
  
  Meissner, Pacinian, Ruffini.
• D. Merkel, free nerve endings, Pacinian: Merkel discs are epidermal slowly-adapting touch cells, not the deep lamellated corpuscle.
  
  Merkel, free nerve endings, Pacinian.

High-Yield Facts:

• Pacinian and Meissner corpuscles are rapidly adapting; Merkel discs and Ruffini endings are slowly adapting.
• Pacinian corpuscle = deep pressure and vibration; Meissner = fine discriminative touch in dermal papillae.
• Ruffini endings detect sustained skin stretch; free nerve endings carry pain and temperature.
• Free nerve endings are the only unencapsulated, unmyelinated cutaneous receptors.

Correct answer: C. Calcium channels close while potassium efflux rises

During the plateau (phase 2) inward L-type calcium current balances outward potassium current. Phase 3 begins when the L-type calcium channels close and the delayed-rectifier potassium channels carry a growing outward current. With inward calcium gone and potassium efflux dominating, the membrane repolarises rapidly back to rest. So phase 3 is calcium channels closing while potassium efflux rises.

Incorrect Options:

• A. Sodium influx while potassium efflux stops: sodium influx is phase 0; potassium efflux actually increases in phase 3.
  
  Sodium influx while potassium efflux stops.
• B. Chloride influx with sodium efflux: chloride and sodium efflux do not drive ventricular phase 3 repolarisation.
  
  Chloride influx with sodium efflux.
• D. Potassium channels close while calcium influx rises: that describes the plateau tendency, the opposite of repolarisation.
  
  Potassium channels close while calcium influx rises.

High-Yield Facts:

• Ventricular phases: 0 sodium influx, 1 transient outward K, 2 calcium plateau, 3 K efflux, 4 resting.
• Phase 3 = L-type calcium channels close plus delayed-rectifier potassium efflux.
• The plateau (phase 2) is unique to cardiac and gives a long refractory period.
• Class III antiarrhythmics block potassium channels and prolong phase 3 and the QT interval.

Correct answer: A. Supraoptic and paraventricular nuclei

The picture is central diabetes insipidus from deficient antidiuretic hormone (vasopressin). Vasopressin (and oxytocin) are made by magnocellular neurons of the supraoptic and paraventricular nuclei, packaged into granules and carried down axons to be stored and released from the posterior pituitary. The supraoptic nucleus is the predominant source of vasopressin. Desmopressin corrects the urine concentration, confirming a central (hypothalamic) rather than renal cause.

Incorrect Options:

• B. Median eminence and thalamic nuclei: the median eminence is a releasing-hormone conduit; the thalamus does not make vasopressin.
  
  Median eminence and thalamic nuclei.
• C. Suprachiasmatic and anteromedial nuclei: the suprachiasmatic nucleus is the circadian clock, not a vasopressin source for the posterior pituitary.
  
  Suprachiasmatic and anteromedial nuclei.
• D. Arcuate and ventromedial nuclei: the arcuate and ventromedial nuclei regulate appetite and anterior-pituitary control, not ADH synthesis.
  
  Arcuate and ventromedial nuclei.

High-Yield Facts:

• ADH and oxytocin are synthesised in the supraoptic and paraventricular nuclei.
• Supraoptic nucleus is the main source of vasopressin; paraventricular of oxytocin.
• Hormones travel down axons and are released from the posterior pituitary (neurohypophysis).
• Central diabetes insipidus responds to desmopressin; nephrogenic does not.