Which cranial nerve is responsible primarily for sensory function?

The olfactory nerve is primarily responsible for sensory function, specifically the sense of smell. It transmits sensory information from the nasal cavity to the brain, enabling the perception of odors. This nerve is unique among cranial nerves as it is purely sensory, making it vital for the olfactory pathway and for recognizing different smells.

In contrast, while other cranial nerves may have sensory components, they also possess motor functions or a combination of both. For example, the trochlear nerve mainly innervates eye muscles for movement, the glossopharyngeal nerve has both sensory and motor functions relating to taste and the gag reflex, and the accessory nerve primarily serves motor functions related to neck and shoulder movement. Therefore, the olfactory nerve stands out for its sole focus on sensory processing, confirming its role as the correct answer in this context.