Editing Olfactory receptor neuron (section)

==Structure==
Humans have between 10 and 20 million olfactory receptor neurons (ORNs).<ref name="McGraw">{{cite book |last1=Saladin |first1=Kenneth |title=Anatomy & physiology : the unity of form and function |date=2012 |publisher=McGraw-Hill |isbn=978-0073378251 |page=593 |edition=6th}}</ref> In [[vertebrates]], ORNs are [[Bipolar neuron|bipolar neurons]] with [[dendrites]] facing the external  surface of the [[cribriform plate]] with axons that pass through the cribriform foramina with terminal end at olfactory bulbs. The ORNs are located in the [[olfactory epithelium]] in the nasal cavity.  The cell bodies of the ORNs are distributed among the [[wikt:stratified|stratified]] layers of the olfactory epithelium.<ref name= Cunningham>{{cite journal |doi=10.1016/s0306-4522(99)00193-1 |pmid=10501454 |title=Olfactory receptor neurons exist as distinct subclasses of immature and mature cells in primary culture |journal=Neuroscience |volume=93 |issue=4 |year=1999 |last1=Cunningham |first1=A.M. |last2=Manis |first2=P.B. |last3=Reed |first3=R.R. |last4=Ronnett |first4=G.V. |pages=1301–12|s2cid=23634746 |doi-access=free }}</ref>

Many tiny hair-like non-motile [[cilia]] protrude from the olfactory receptor cell's [[dendrite]]s. The dendrites extend to the olfactory epithelial surface and each ends in a dendritic knob from which around 20 to 35 cilia protrude. The cilia have a length of up to 100 micrometres and with the cilia from other dendrites form a meshwork in the olfactory [[mucus]].<ref name="McClintock">{{cite journal |last1=McClintock |first1=TS |last2=Khan |first2=N |last3=Xie |first3=C |last4=Martens |first4=JR |title=Maturation of the Olfactory Sensory Neuron and Its Cilia. |journal=Chemical Senses |date=5 December 2020 |volume=45 |issue=9 |pages=805–822 |doi=10.1093/chemse/bjaa070 |pmid=33075817|pmc=8133333 }}</ref>  The surface of the cilia is covered with [[olfactory receptor]]s, a type of [[G protein-coupled receptor]]. Each olfactory receptor cell [[Gene expression|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 [[glomerulus (olfaction)|glomeruli]] in the [[olfactory bulb]].<ref>{{cite journal|last1=McEwen|first1=D. P|title=Olfactory cilia: our direct neuronal connection to the external world.|journal=Curr. Top. Dev. Biol.|date=2008|volume=85|pages=333–370|doi=10.1016/S0070-2153(08)00812-0|pmid=19147011|series=Current Topics in Developmental Biology|isbn=9780123744531}}</ref>