Which cranial nerve functions primarily in the sense of smell?

The olfactory nerve, also known as cranial nerve I, is responsible for the sense of smell. This nerve is vital for detecting odor molecules that bind to olfactory receptors in the nasal cavity, allowing the brain to interpret various smells. It is unique among cranial nerves as it directly connects with the brain's olfactory bulb instead of passing through the brainstem.

The other cranial nerves listed have distinct functions unrelated to the sense of smell. The optic nerve (cranial nerve II) is focused on vision, conveying visual information from the retina to the brain. The oculomotor nerve (cranial nerve III) primarily controls eye movements and pupil constriction. The trochlear nerve (cranial nerve IV) is involved in controlling the superior oblique muscle of the eye, which affects eye rotation. Understanding the specific functions of these nerves clarifies why cranial nerve I is the correct answer for the sense of smell.