The suprachiasmatic nucleus (SCN) of the hypothalamus serves as the master circadian clock in mammals. Which neural pathway is primarily responsible for entraining this clock to the environmental light-dark cycle?
- A Medial forebrain bundle
- B Retinohypothalamic tract ✓
- C Mammillothalamic tract
- D Stria terminalis
Correct answer: B. Retinohypothalamic tract
Explanation
The retinohypothalamic tract carries photic information directly from melanopsin-containing retinal ganglion cells to the SCN, entraining circadian rhythms to the light-dark cycle. The medial forebrain bundle connects the hypothalamus to the brainstem and is involved in reward. The mammillothalamic tract connects mammillary bodies to the anterior thalamic nucleus and is part of the Papez circuit. The stria terminalis is an amygdalar efferent pathway.
Reference: Ganong's Review of Medical Physiology, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.