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Olfactory receptor neuron

Olfactory receptor neuron
Labels in German. "Zellen" = "cell","riech" = "smell", "Riechnerv" = olfactory nerve, "cillien" = cilia.
Location olfactory epithelium in the nose
Morphology Bipolar sensory receptor
Function Detect traces of chemicals in inhaled air (sense of smell)
Neurotransmitter Glutamate[1]
Presynaptic connections None
Postsynaptic connections Olfactory bulb
Gray's p.996
Code TH H3.
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TH Template:Str mid/core.html {{#property:P1694}}
TE {{#property:P1693}}
FMA Template:FMA
Anatomical terminology
Plan of olfactory neurons.

An olfactory receptor neuron (ORN), also called an olfactory sensory neuron (OSN), is a transduction cell within the olfactory system.[2]


Humans have about 40 million olfactory receptor neurons that detect more than one trillion different odors.[3] In vertebrates, ORNs are bipolar neurons with dendrites facing the inferior space of the nasal cavity and an axon that passes through the cribiform plate then travels along the olfactory nerve to the olfactory bulb. The ORNs are located in the olfactory epithelium in the nasal cavity. The cell bodies of the ORNs are distributed among all three of the stratified layers of the olfactory epithelium.[4]


Many tiny hair-like cilia protrude from the olfactory receptor cell's dendrite into the mucus covering the surface of the olfactory epithelium. The surface of these cilia is covered with olfactory receptors, a type of G protein-coupled receptor. Each olfactory receptor cell expresses 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 in the olfactory bulb.[citation needed]


ORs, which are located on the membranes of the cilia have been classified as a complex type of ligand-gated metabotropic channels.[5] 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.[6][7] The activated OR in turn activates the intracellular G-protein, GOLF (GNAL), adenylate cyclase and production of cyclic AMP (cAMP) opens ion channels in the cell membrane, resulting in an influx of sodium and calcium ions into the cell, and an efflux of chloride ions. This influx of positive ions and efflux of negative ions causes the neuron to depolarize, generating an action potential.


In insects, olfactory receptor neurons typically reside on the antenna. Much like in vertebrates, axons from the sensory neurons converge into glomeruli in the antennal lobe.[citation needed]

See also


  1. ^ Berkowicz, D. A.; Trombley, P. Q.; Shepherd, G. M. (1994). "Evidence for glutamate as the olfactory receptor cell neurotransmitter". Journal of neurophysiology 71 (6): 2557–61. PMID 7931535. 
  2. ^ Vermeulen, A; Rospars, J. P. (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". Journal of computational neuroscience 5 (3): 243–66. PMID 9663551. 
  3. ^ Bushdid, C.; Magnasco, M. O.; Vosshall, L. B.; Keller, A. (2014). "Humans Can Discriminate More than 1 Trillion Olfactory Stimuli". Science 343 (6177). Bibcode:2014Sci...343.1370B. PMID 24653035. doi:10.1126/science.1249168. 
  4. ^ Cunningham, A.M.; Manis, P.B.; Reed, R.R.; Ronnett, G.V. (1999). "Olfactory receptor neurons exist as distinct subclasses of immature and mature cells in primary culture". Neuroscience 93 (4). PMID 10501454. doi:10.1016/s0306-4522(99)00193-1. 
  5. ^ Touhara, Kazushige (2009). "Insect Olfactory Receptor Complex Functions as a Ligand-gated Ionotropic Channel". Annals of the New York Academy of Sciences 1170: 177–80. Bibcode:2009NYASA1170..177T. PMID 19686133. doi:10.1111/j.1749-6632.2009.03935.x. 
  6. ^ Bieri, S.; Monastyrskaia, K; Schilling, B (2004). "Olfactory Receptor Neuron Profiling using Sandalwood Odorants". Chemical Senses 29 (6): 483–7. PMID 15269120. doi:10.1093/chemse/bjh050. 
  7. ^ Fan, Jinhong; Ngai, John (2001). "Onset of Odorant Receptor Gene Expression during Olfactory Sensory Neuron Regeneration". Developmental Biology 229 (1): 119–27. PMID 11133158. doi:10.1006/dbio.2000.9972. 

External links