Which cranial nerve is responsible for the sense of smell?

The cranial nerve responsible for the sense of smell is the olfactory nerve, or cranial nerve I.

The olfactory nerve is a sensory nerve made of many small bundles of fibers from receptor cells in the upper nasal cavity. When odor molecules reach the olfactory lining during inhalation, these receptor cells convert chemical information into electrical signals.

The fibers pass through tiny openings in the cribriform plate, a sieve-like part of the ethmoid bone, and connect with the olfactory bulb. Signals then travel through the olfactory tract to brain regions involved in identifying smells, memory, and emotion. This close connection helps explain why particular odors can evoke vivid memories.

The olfactory nerve is unusual among the cranial nerves. It is the first cranial nerve, does not emerge from the brainstem, and has some capacity for regeneration because new olfactory receptor neurons can develop. Damage may cause anosmia, or loss of smell. The trigeminal nerve can detect irritation, temperature, and pain in the nose, but it does not carry the primary sense of smell.