A medical student working night shifts has reduced nocturnal melatonin secretion and disturbed sleep. The sympathetic pathway that delivers the light-dark signal from the retina to the pineal gland relays through which final ganglion?
- A Superior cervical ganglion ✓
- B Ciliary ganglion
- C Stellate ganglion
- D Pterygopalatine ganglion
Correct answer: A. Superior cervical ganglion
Explanation
Retinal fibres project via the retinohypothalamic tract to the suprachiasmatic nucleus, then to the paraventricular nucleus, descending to the intermediolateral column and out to the superior cervical ganglion. Postganglionic sympathetic fibres from this ganglion reach the pineal gland and stimulate N-acetyltransferase, the rate limiting enzyme of melatonin synthesis. The ciliary ganglion carries parasympathetic fibres for pupillary constriction and plays no role in pineal innervation.
Reference: Ganong's Review of Medical Physiology, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.