In pineal physiology, environmental light information reaches the gland through which pathway, enabling nocturnal melatonin synthesis?

• A Retina to lateral geniculate body to occipital cortex to pineal via thalamocortical fibres
• B Retina to suprachiasmatic nucleus to paraventricular nucleus to intermediolateral column to superior cervical ganglion to pineal ✓
• C Direct optic nerve fibres terminating on pinealocytes
• D Retina to olfactory bulb to limbic structures to pineal via fornix

Explanation

Light information travels from retinal ganglion cells via the retinohypothalamic tract to the suprachiasmatic nucleus, then to the paraventricular nucleus, descending sympathetic pathways, the superior cervical ganglion, and finally noradrenergic fibres to the pineal. Darkness permits norepinephrine release, raising intracellular cAMP and inducing N-acetyltransferase for melatonin synthesis. There are no direct optic fibres to the pineal, ruling out option C.

Reference: Ganong Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.