The olfactory nerve, also known as the first cranial nerve, cranial nerve I, or simply CN I,<!--Each CN article, CN 0 plus CN I to CN XII, should not fail to have the standard, established synonyms at outset, nor be styled substantially differently from the others; do not change this aspect of any particular one of them without first discussing the same change for all of them.--> is a cranial nerve that contains sensory nerve fibers relating to the sense of smell.
The afferent nerve fibers of the olfactory receptor neurons transmit nerve impulses about odors to the central nervous system (olfaction). Derived from the embryonic nasal placode, the olfactory nerve is somewhat unusual among cranial nerves because it is capable of some regeneration if damaged. The olfactory nerve is sensory in nature and originates on the olfactory mucosa in the upper part of the nasal cavity. From the olfactory mucosa, the nerve (actually many small nerve fascicles) travels up through the cribriform plate of the ethmoid bone to reach the surface of the brain. Here the fascicles enter the olfactory bulb and synapse there; from the bulbs (one on each side) the olfactory information is transmitted into the brain via the olfactory tract. The fascicles of the olfactory nerve are not visible on a cadaver brain because they are severed upon removal.
Structure
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 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, a sieve-like structure of the ethmoid bone.
The sense of smell arises from the stimulation of receptors by small molecules in inspired air of varying spatial, chemical, and electrical properties that reach the nasal epithelium in the nasal cavity during inhalation. These stimulants are transduced into electrical activity in the olfactory neurons, which then transmit these impulses to the olfactory bulb and from there they reach the olfactory areas of the brain via the olfactory tract.
The olfactory nerve is the shortest of the twelve cranial nerves and, similar to the optic nerve, does not emanate from the brainstem. Odorants interact with the olfactory receptor neurons (ORNs) at the periphery and transmit olfactory information to the central nervous system via axons at the basal surface. Therefore, the olfactory nerve works to transduce sensory stimuli in the form of odorants and encode them into electrical signals, which are relayed to higher-order centers through synaptic transmission. Therefore, ORNs maintain a normal cycle of degeneration and regeneration. It can be harmful when the particles are soot or magnetite in air pollution.
In naegleriasis, "brain-eating" amoeba enter through the olfactory mucosa of the nasal tissues and follow the olfactory nerve fibers into the olfactory bulbs and then the brain.
Additional images
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File:Slide21ior.JPG|Olfactory nerve, deep dissection, inferior view
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See also
- Anterior olfactory nucleus
- Phantosmia