What is the primary function of the olfactory nerve (CN I)?

The olfactory nerve, also known as cranial nerve I, is primarily responsible for the sense of smell. This nerve is unique in that it is the only cranial nerve directly involved in the sensory functions of smell. It transmits sensory information from the olfactory epithelium in the nasal cavity to the olfactory bulb in the brain, enabling the perception of odors. The olfactory nerve plays a critical role in the detection of volatile substances, which is essential for identifying food, detecting hazards like smoke or gas, and even for social interactions linked to scent.

In contrast, the other options pertain to entirely different sensory modalities or functions. The sense of touch involves a different set of nerve pathways, while the sense of hearing is served by the vestibulocochlear nerve (cranial nerve VIII). Muscle control of the eye is primarily the function of the oculomotor, trochlear, and abducens nerves, not the olfactory nerve. Thus, the olfactory nerve's distinct role in providing the sense of smell clearly defines its primary function.