Olfactory nerve
Encyclopedia
The olfactory nerve, or cranial nerve I, is the first of twelve cranial nerves
. It is instrumental in the sense of smell
. Derived from the embryo
nic nasal placode
, the olfactory nerve is capable of regeneration.
s 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 as do the remaining cranial nerves. Rather, they 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 neuron
s 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 olfactory (or odorant) receptors
by small molecules of different spatial, chemical, and electrical properties that pass over the nasal epithelium in the nasal cavity during inhalation. These interactions are transduced into electrical activity in 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 the twelve cranial nerves and only one of two cranial nerves (the other being the optic nerve
) that do not join with the brainstem.
s and place a pungent odor (such as damp coffee essence) under the open nostril. The test is then repeated on the other nostril.
Cranial nerves
Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves...
. It is instrumental in the sense of smell
Olfaction
Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...
. Derived from the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
nic nasal placode
Nasal placode
The nasal placode gives rise to the olfactory epithelium of the nose.The terms "nasal sac" or "nasal pit" are sometimes used to describe an intermediate structure arising between the placode and epithelium chronologically....
, the olfactory nerve is capable of regeneration.
Anatomy
The specialized olfactory receptor neuronOlfactory receptor neuron
An olfactory receptor neuron , also called an olfactory sensory neuron , is a transduction cell within the olfactory system. J. Rospars, Dendritic integration in olfactory sensory neurons: a steady-state analysis of how the neuron structure and neuron environment influence the coding of odor...
s of the olfactory nerve are located in the olfactory mucosa of the upper parts of the nasal cavity
Nasal cavity
The nasal cavity is a large air filled space above and behind the nose in the middle of the face.- Function :The nasal cavity conditions the air to be received by the other areas of the respiratory tract...
. The olfactory nerves do not form two trunks as do the remaining cranial nerves. Rather, they consist of a collection of many sensory nerve fibers that extend from the olfactory epithelium to the olfactory bulb
Olfactory bulb
The olfactory bulb is a structure of the vertebrate forebrain involved in olfaction, the perception of odors.-Anatomy:In most vertebrates, the olfactory bulb is the most rostral part of the brain. In humans, however, the olfactory bulb is on the inferior side of the brain...
, passing through the many openings of the Cribriform plate of the Ethmoid bone, a sieve
Sieve
A sieve, or sifter, separates wanted elements from unwanted material using a woven screen such as a mesh or net. However, in cooking, especially with flour, a sifter is used to aerate the substance, among other things. A strainer is a type of sieve typically used to separate a solid from a liquid...
-like structure.
Olfactory receptor neuron
Olfactory receptor neuron
An olfactory receptor neuron , also called an olfactory sensory neuron , is a transduction cell within the olfactory system. J. Rospars, Dendritic integration in olfactory sensory neurons: a steady-state analysis of how the neuron structure and neuron environment influence the coding of odor...
s continue to be born throughout life and extend new axons to the olfactory bulb
Olfactory bulb
The olfactory bulb is a structure of the vertebrate forebrain involved in olfaction, the perception of odors.-Anatomy:In most vertebrates, the olfactory bulb is the most rostral part of the brain. In humans, however, the olfactory bulb is on the inferior side of the brain...
. 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
Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...
(olfaction) arises from the stimulation of olfactory (or odorant) receptors
Olfactory receptor
Olfactory receptors expressed in the cell membranes of olfactory receptor neurons are responsible for the detection of odor molecules. Activated olfactory receptors are the initial player in a signal transduction cascade which ultimately produces a nerve impulse which is transmitted to the brain...
by small molecules of different spatial, chemical, and electrical properties that pass over the nasal epithelium in the nasal cavity during inhalation. These interactions are transduced into electrical activity in the olfactory bulb, which then transmits the electrical activity to other parts of the olfactory system
Olfactory system
The olfactory system is the sensory system used for olfaction, or the sense of smell. Most mammals and reptiles have two distinct parts to their olfactory system: a main olfactory system and an accessory olfactory system. The main olfactory system detects volatile, airborne substances, while the...
and the rest of the central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
via the olfactory tract.
The olfactory nerve is the shortest of the twelve cranial nerves and only one of two cranial nerves (the other being the optic nerve
Optic nerve
The optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.-Anatomy:The optic nerve is the second of...
) that do not join with the brainstem.
Testing
To test the function of the olfactory nerve, doctors block one of the patient's nostrilNostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
s 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 as 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).See also
- Anterior olfactory nucleusAnterior olfactory nucleusThe anterior olfactory nucleus is a portion of the forebrain of vertebrates.It is involved in olfaction.-Location:...
- Nasal administrationNasal administrationNasal administration can be used to deliver drugs for either local or systemic effect. Locally acting drugs are for example decongestants and allergy treatments...
: olfactory transfer - List of mnemonics for the cranial nerves