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

The olfactory nerve, also known as cranial nerve I, is primarily responsible for the sense of smell. It carries sensory information from the olfactory epithelium in the nasal cavity to the brain, specifically to the olfactory bulb. This nerve is unique in that it provides direct input to the central nervous system, allowing for the perception of odors, which plays a crucial role in taste and the emotional responses associated with scents.

The other options refer to different sensory functions: sight is mediated by the optic nerve, sound by the vestibulocochlear nerve, and balance is also partially associated with the vestibulocochlear nerve. Therefore, the primary role of the olfactory nerve is distinct and centers solely on the detection and transmission of olfactory information, which is why it is correct to identify it as the nerve responsible for the sense of smell.