The olfactory nerve is one of the twelve cranial nerves that emerge directly from the base of the brain. Also called cranial nerve I (CN I), it is the first and shortest of the twelve. The olfactory nerve is formed by axons from specialized olfactory receptor neurons which are situated in the olfactory mucosa of the upper parts of the nasal cavity. These same nerve cells also projects axons that extend from the olfactory epithelium to the olfactory bulb, passing through the many openings of the cribriform plate of the ethmoid bone.
The nerve cells in the nasal cavity are chemosensitive and respond to chemical signals which are converted to electrical impulses that are carried up through the cranial nerve I to the olfactory bulb. The axons that make up the olfactory nerve continually regenerate throughout life as they project towards the olfactory bulb.