Melanopsin is a photopigment found predominantly in a specialized subset of retinal ganglion cells known as intrinsically photosensitive retinal ganglion cells (ipRGCs). Unlike rods and cones, which are responsible for image-forming vision, these ganglion cells play critical roles in regulating circadian rhythms, pupil responses to light, and other non-image-forming functions.

Location of Melanopsin

• Melanopsin is exclusively present in retinal ganglion cells in the inner retina, specifically the ipRGC subtype.wikipedia+2

• It is not found in rods, cones, or bipolar cells as the primary photopigment.

• Although a very small fraction of cones in the peripheral retina may express melanopsin, this is minimal and not significant for its main functions.wikipedia

Function of Melanopsin-Containing Retinal Ganglion Cells

• These cells are sensitive to blue light (wavelength ~470-480 nm).

• They send signals to the brain’s circadian clock (suprachiasmatic nucleus) to regulate sleep-wake cycles.

• They contribute to the pupillary light reflex and other subconscious light responses, independent of image vision.pnas+1

Conclusion

Melanopsin is located in retinal ganglion cells, specifically the subset involved in photosensitive non-image visual functions.

The correct answer is:

(3) Ganglion cells