An olfactory receptor neuron (ORN), also called an olfactory sensory neuron (OSN), is a transduction

Transduction

Transduction is a mechanism whereby genetic material may be transferred from the genes of a bacterium to another bacterium. This may include the actual covalent-bonding of new genetic markers...

 cell within 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...

. J. Rospars, (1998) Dendritic integration in olfactory sensory neurons: a steady-state analysis of how the neuron structure and neuron environment influence the coding of odor intensity. J Comput Neurosci. 5: 243-266. PMID 9663551

Vertebrates

Humans have about 40 million olfactory receptors that detect up to 10,000 different odors. In vertebrates, ORNs are bipolar neurons with dendrites facing the interior space of the nasal cavity and an axon

Axon

An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....

 that passes through the cribiform plate then travels along the olfactory nerve

Olfactory nerve

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 embryonic nasal placode, the olfactory nerve is capable of regeneration.-Anatomy:...

 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...

. The ORNs are located in the olfactory epithelium

Olfactory epithelium

The olfactory epithelium is a specialized epithelial tissue inside the nasal cavity that is involved in smell. In humans, it measures about 1 square centimetre and lies on the roof of the nasal cavity about 7 cm above and behind the nostrils...

 in the nasal cavity. The cell bodies of the ORNs are distributed among all three of the stratified layers of the olfactory epithelium.

Structure

Many tiny hair-like cilia protrude from the olfactory receptor cell's dendrite into the mucus

Mucus

In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...

 covering the surface of the olfactory epithelium. The surface of these cilia is covered with olfactory receptor

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...

s, a type of G protein-coupled receptor

G protein-coupled receptor

G protein-coupled receptors , also known as seven-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptor, and G protein-linked receptors , comprise a large protein family of transmembrane receptors that sense molecules outside the cell and activate inside signal...

. Each olfactory receptor cell expresses

Gene expression

Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...

 only one type of olfactory receptor (OR), but many separate olfactory receptor cells express ORs which bind the same set of odors. The axons of olfactory receptor cells which express the same OR converge to form glomeruli

Glomerulus (olfaction)

The glomerulus is a spherical structure located in the olfactory bulb of the brain where synapses form between the terminals of the olfactory nerve and the dendrites of mitral, periglomerular and tufted cells...

 in 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...

.

Function

ORs, which are located on the membranes of the cilia have been classified as a complex type of ligand-gated metabotropic channels. There are approximately 1000 different genes that code for the ORs, making them the largest gene family. An odorant will dissolve into the mucus of the olfactory epithelium and then bind to an OR. ORs can bind to a variety of odor molecules, with varying affinities. The difference in affinities causes differences in activation patterns resulting in unique odorant profiles.
An olfactory receptor neuron (ORN), also called an olfactory sensory neuron (OSN), is a transduction

Transduction

Transduction is a mechanism whereby genetic material may be transferred from the genes of a bacterium to another bacterium. This may include the actual covalent-bonding of new genetic markers...

 cell within 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...

. J. Rospars, (1998) Dendritic integration in olfactory sensory neurons: a steady-state analysis of how the neuron structure and neuron environment influence the coding of odor intensity. J Comput Neurosci. 5: 243-266. PMID 9663551

Vertebrates

Humans have about 40 million olfactory receptors that detect up to 10,000 different odors. In vertebrates, ORNs are bipolar neurons with dendrites facing the interior space of the nasal cavity and an axon

Axon

An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....

 that passes through the cribiform plate then travels along the olfactory nerve

Olfactory nerve

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 embryonic nasal placode, the olfactory nerve is capable of regeneration.-Anatomy:...

 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...

. The ORNs are located in the olfactory epithelium

Olfactory epithelium

The olfactory epithelium is a specialized epithelial tissue inside the nasal cavity that is involved in smell. In humans, it measures about 1 square centimetre and lies on the roof of the nasal cavity about 7 cm above and behind the nostrils...

 in the nasal cavity. The cell bodies of the ORNs are distributed among all three of the stratified layers of the olfactory epithelium.

Structure

Many tiny hair-like cilia protrude from the olfactory receptor cell's dendrite into the mucus

Mucus

In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...

 covering the surface of the olfactory epithelium. The surface of these cilia is covered with olfactory receptor

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...

s, a type of G protein-coupled receptor

G protein-coupled receptor

G protein-coupled receptors , also known as seven-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptor, and G protein-linked receptors , comprise a large protein family of transmembrane receptors that sense molecules outside the cell and activate inside signal...

. Each olfactory receptor cell expresses

Gene expression

Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...

 only one type of olfactory receptor (OR), but many separate olfactory receptor cells express ORs which bind the same set of odors. The axons of olfactory receptor cells which express the same OR converge to form glomeruli

Glomerulus (olfaction)

The glomerulus is a spherical structure located in the olfactory bulb of the brain where synapses form between the terminals of the olfactory nerve and the dendrites of mitral, periglomerular and tufted cells...

 in 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...

.

Function

ORs, which are located on the membranes of the cilia have been classified as a complex type of ligand-gated metabotropic channels. K. Touhara, (2009) Insect olfactory receptor complex functions as a ligand-gated ionotropic channel 1170 International Symposium on Olfaction and Taste: Ann. N.Y. Acad. Sci. 177-180 PMID 19686133 There are approximately 1000 different genes that code for the ORs, making them the largest gene family. An odorant will dissolve into the mucus of the olfactory epithelium and then bind to an OR. ORs can bind to a variety of odor molecules, with varying affinities. The difference in affinities causes differences in activation patterns resulting in unique odorant profiles.S. Bieri, K. Monastyrskaia, B. Schilling, (2004) Olfactory receptor neuron profiling using sandalwood odorants. Chem. Senses 29:483-487 PMID 15269120
An olfactory receptor neuron (ORN), also called an olfactory sensory neuron (OSN), is a transduction

Transduction

Transduction is a mechanism whereby genetic material may be transferred from the genes of a bacterium to another bacterium. This may include the actual covalent-bonding of new genetic markers...

 cell within 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...

. J. Rospars, (1998) Dendritic integration in olfactory sensory neurons: a steady-state analysis of how the neuron structure and neuron environment influence the coding of odor intensity. J Comput Neurosci. 5: 243-266. PMID 9663551

Vertebrates

Humans have about 40 million olfactory receptors that detect up to 10,000 different odors. In vertebrates, ORNs are bipolar neurons with dendrites facing the interior space of the nasal cavity and an axon

Axon

An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....

 that passes through the cribiform plate then travels along the olfactory nerve

Olfactory nerve

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 embryonic nasal placode, the olfactory nerve is capable of regeneration.-Anatomy:...

 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...

. The ORNs are located in the olfactory epithelium

Olfactory epithelium

The olfactory epithelium is a specialized epithelial tissue inside the nasal cavity that is involved in smell. In humans, it measures about 1 square centimetre and lies on the roof of the nasal cavity about 7 cm above and behind the nostrils...

 in the nasal cavity. The cell bodies of the ORNs are distributed among all three of the stratified layers of the olfactory epithelium.

Structure

Many tiny hair-like cilia protrude from the olfactory receptor cell's dendrite into the mucus

Mucus

In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...

 covering the surface of the olfactory epithelium. The surface of these cilia is covered with olfactory receptor

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...

s, a type of G protein-coupled receptor

G protein-coupled receptor

G protein-coupled receptors , also known as seven-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptor, and G protein-linked receptors , comprise a large protein family of transmembrane receptors that sense molecules outside the cell and activate inside signal...

. Each olfactory receptor cell expresses

Gene expression

Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...

 only one type of olfactory receptor (OR), but many separate olfactory receptor cells express ORs which bind the same set of odors. The axons of olfactory receptor cells which express the same OR converge to form glomeruli

Glomerulus (olfaction)

The glomerulus is a spherical structure located in the olfactory bulb of the brain where synapses form between the terminals of the olfactory nerve and the dendrites of mitral, periglomerular and tufted cells...

 in 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...

.

Function

ORs, which are located on the membranes of the cilia have been classified as a complex type of ligand-gated metabotropic channels. K. Touhara, (2009) Insect olfactory receptor complex functions as a ligand-gated ionotropic channel 1170 International Symposium on Olfaction and Taste: Ann. N.Y. Acad. Sci. 177-180 PMID 19686133 There are approximately 1000 different genes that code for the ORs, making them the largest gene family. An odorant will dissolve into the mucus of the olfactory epithelium and then bind to an OR. ORs can bind to a variety of odor molecules, with varying affinities. The difference in affinities causes differences in activation patterns resulting in unique odorant profiles.S. Bieri, K. Monastyrskaia, B. Schilling, (2004) Olfactory receptor neuron profiling using sandalwood odorants. Chem. Senses 29:483-487 PMID 15269120 J. Fan and J. Ngai, (2001) Onset of odorant receptor gene expression during olfactory sensory neuron regeneration. Dev Biol. 229: 119-127 PMID 11133158 The activated OR in turn activates the intracellular G-protein, GOLF (GNAL

GNAL

Guanine nucleotide-binding protein G subunit alpha is a protein that in humans is encoded by the GNAL gene.-Further reading:...

), adenylate cyclase

Adenylate cyclase

Adenylate cyclase is part of the G protein signalling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell ....

 and production of cyclic AMP (cAMP) opens ion channels in the cell membrane

Cell membrane

The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

, resulting in an influx of sodium

Sodium

Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 and calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 ions into the cell, and an efflux of chloride

Chloride

The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...

 ions. This influx of positive ions and efflux of negative ions causes the neuron to depolarize, generating an action potential

Action potential

In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...

.

Insects

In insect

Insect

Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s, olfactory receptor neurons typically reside on the antenna

Antenna (biology)

Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....

. Much like in vertebrates, axons from the sensory neurons converge into glomeruli in the antennal lobe

Antennal lobe

The antennal lobe is the deutocerebral neuropil of insect which receives the input from the olfactory sensory neurons on the antenna. Functionally, it shares some similarities with the olfactory bulb in vertebrates....

.

External links

• NIF Search - Olfactory receptor neuron via the Neuroscience Information Framework
  Neuroscience Information Framework
  The Neuroscience Information Framework is a repository of global neuroscience web resources, including experimental, clinical, and translational neuroscience databases, knowledge bases, atlases, and genetic/genomic resources.-Description:...