olfactory nerve

Nerve: Olfactory nerve
Latin	nervus olfactorius
Gray's	subject #196
MeSH	Olfactory+Nerve

The olfactory nerve, or cranial nerve I, is the first of twelve cranial nerves. The specialized olfactory receptor neurons of the olfactory nerve are located in the olfactory mucosa of the upper parts of the nasal cavity. The olfactory nerves do not form two trunks like the remaining cranial nerves, but consist of a collection of many sensory nerve fibers that extend from the olfactory epithelium to the olfactory bulb, passing through the many openings of the Cribriform plate of the Ethmoid bone; a sieve-like structure.

Olfactory receptor neurons continue to be born throughout life and extend new axons to the olfactory bulb. Olfactory ensheathing glia wrap bundles of these axons and are thought to facilitate their passage into the central nervous system.

The sense of smell (olfaction) arises from the stimulation of the olfactory receptors by activation from gas molecules that pass by the nose during respiration. The resulting electrical activity is transduced into the olfactory bulb which then transmits the electrical activity to other parts of the olfactory system and the rest of the central nervous system via the olfactory tract.

The olfactory nerve is the shortest of all the twelve cranial nerves and only one of two cranial nerves (the other being the optic nerve) that do not join with the brainstem.

Testing

To test the function of the olfactory nerve, doctors block one of the patient's nostrils and place a pungent odor (such as damp coffee essence) under the open nostril. The test is then repeated on the other nostril.

Lesions

Lesions to the olfactory nerve can occur because of blunt trauma, such a coup-contra-coup damage, meningitis and tumors of the frontal lobe. They often lead to a reduced ability to taste and smell. However, lesions of the olfactory nerve do not lead to a reduced ability to sense pain from the nasal epithelium. This is because pain from the nasal epithelium is not carried to the central nervous system by the olfactory nerve; rather, it is carried to the central nervous system by the trigeminal nerve (cranial nerve V).

Additional images

See also

• Anterior olfactory nucleus
• Nasal administration: olfactory transfer
• List of mnemonics for the cranial nerves

External links

• Cranial Nerves at Yale 1-1
• cranialnerves at The Anatomy Lesson by Wesley Norman (Georgetown University) (I)