main olfactory receptor neuron
Acronym:
ORNm
The term main olfactory receptor neuron (ORNm) refers to one of two kinds of olfactory receptor neuron (ORN). The other is the accessory olfactory receptor neuron (ORNa). ORNm's are far more numerous and respond to a vastly wider range of oderants than ORNa's. Their oderant-sensitive dendritic fibers and cell bodies are embedded in the main olfactory epithelium (OLEm), which lines the underside of the cribriform plate, the thin bony structure that separates the nasal cavity below from the cranial cavity above. Their axons project via the terminal nerve (trm) through the cribriform plate to the main olfactory bulb (MOB). The ORNm is considered a part of the instinctive control system in the neurobehavioral control model ( Bowden-2022 ).
ORNm's are found in the human ( Buck-2013 ), macaque ( Price-1990 ), rat and mouse ( Barral-2009 ). They differ from ORNa's in that ORNa's respond solely to a small number of social oderants secreted by members of the same rodent species. ORNm's, on the other hand, respond to all classes of oderants and are found in primates as well as rodents.
ORNm variants are randomly distributed within overlapping olfactory zones (OLZ) of the OLEm. Each receptor neuron is responsive to a single variant of oderant molecule. Axons from a distributed ensemble of receptors for the same oderant molecule project to a single neuron in the main olfactory bulb (MOB) ( Menini-2004 ).
The physiological function of OLRm's is to transduce the chemical signals of tens of thousands of unique oderant molecules into electrochemical signals for neural processing and transmission and reprocessing through the main olfactory system (OSYm). In the human, the total number of OLRm's on the two sides of the nose is ~10,000,000 ( Wikipedia ). The number of molecular variants in humans is ~350 ( Buck-2013 ), in the rat ~1400 ) and in the mouse ~1000 ( Wikipedia. The number of possible combinations and permutations of human's 350 oderant variants (350-squared) is 122,500...more than enough to account for the human ability to detect ~5,000 to10,000 complex smells ( Buck-2013 ).
The smell that one perceives consciously is associated with the excitation of neurons in cerebral cortex that receive highly processed input from the unique combination of OLR's activated by volatile molecules emanating from a given stimulus ( Buck-2013 ). Some oderants are sensed as pleasant smells, such as those of fresh food, flowers and perfume, others as unpleasant smells of, for example, decaying vegetable matter, putrifying meat and excretory waste ( Buck-2013 ). Final 1 Feb 2025.
Also known as: main olfactory receptorNeuroNames ID : 5717
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