The vomeronasal organ (VNO), or Jacobson's organ, is the paired auxiliary
olfactory
The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste.
In humans, it ...
(smell)
sense organ
A sense is a biological system used by an organism for sensation, the process of gathering information about the surroundings through the detection of Stimulus (physiology), stimuli. Although, in some cultures, five human senses were traditio ...
located in the
soft tissue
Soft tissue connective tissue, connects and surrounds or supports internal organs and bones, and includes muscle, tendons, ligaments, Adipose tissue, fat, fibrous tissue, Lymphatic vessel, lymph and blood vessels, fasciae, and synovial membranes.� ...
of the
nasal septum
The nasal septum () separates the left and right airways of the Human nose, nasal cavity, dividing the two nostrils.
It is Depression (kinesiology), depressed by the depressor septi nasi muscle.
Structure
The fleshy external end of the nasal s ...
, in the
nasal cavity
The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nas ...
just above the roof of the mouth (the
hard palate
The hard palate is a thin horizontal bony plate made up of two bones of the facial skeleton, located in the roof of the mouth. The bones are the palatine process of the maxilla and the horizontal plate of palatine bone. The hard palate spans ...
) in various
tetrapods
A tetrapod (; from Ancient Greek τετρα- ''(tetra-)'' 'four' and πούς ''(poús)'' 'foot') is any four- limbed vertebrate animal of the clade Tetrapoda (). Tetrapods include all extant and extinct amphibians and amniotes, with the lat ...
. The name is derived from the fact that it lies adjacent to the unpaired
vomer
The vomer (; ) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones. The vomer forms ...
bone (from Latin , for its shape) in the nasal septum. It is present and functional in all
snake
Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...
s and
lizard
Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...
s, and in many
mammal
A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...
s, including
cat
The cat (''Felis catus''), also referred to as the domestic cat or house cat, is a small domesticated carnivorous mammal. It is the only domesticated species of the family Felidae. Advances in archaeology and genetics have shown that the ...
s,
dog
The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the gray wolf. Also called the domestic dog, it was selectively bred from a population of wolves during the Late Pleistocene by hunter-gatherers. ...
s,
cattle
Cattle (''Bos taurus'') are large, domesticated, bovid ungulates widely kept as livestock. They are prominent modern members of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Mature female cattle are calle ...
,
pig
The pig (''Sus domesticus''), also called swine (: swine) or hog, is an omnivorous, domesticated, even-toed, hoofed mammal. It is named the domestic pig when distinguishing it from other members of the genus '' Sus''. Some authorities cons ...
s, and some
primate
Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...
s.
Human
Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...
s may have physical remnants of a VNO, but it is
vestigial
Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
and non-functional.
The VNO contains the
cell bodies of
sensory neuron
Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded receptor potentials. This process is called sensory transduc ...
s which have receptors that detect specific
non-volatile
Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data.
Non-volatile memory typ ...
(liquid)
organic compound
Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...
s which are conveyed to them from the environment. These compounds emanate from
prey
Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not ki ...
,
predator
Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...
s, and the compounds called
sex pheromones from potential
mates
Mates is an English surname, and may refer to:
* Mates (born 1964), British newsreader and journalist
* Michael Mates (born 1934), British politician
* Frederick S. Mates, founded the Mates Investment Fund in 1967 that crashed in the bear market ...
. Activation of the VNO triggers an appropriate behavioral response to the presence of one of these three.
VNO neurons are activated by the binding of certain chemicals to their
G protein-coupled receptor
G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of evolutionarily related ...
s: they express receptors from three families, called V1R,
V2R, and FPR.
The
axon
An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences) is a long, slender cellular extensions, projection of a nerve cell, or neuron, ...
s from these neurons, called
cranial nerve zero
The terminal nerve, also known as cranial nerve zero or simply as CN 0, is a nerve that was not included in the seminal classification of the cranial nerves as CN I through CN XII, but has since been recognized and listed in Terminologia Anatomic ...
(CN 0), project to the
accessory olfactory bulb, which targets the
amygdala
The amygdala (; : amygdalae or amygdalas; also '; Latin from Greek language, Greek, , ', 'almond', 'tonsil') is a paired nucleus (neuroanatomy), nuclear complex present in the Cerebral hemisphere, cerebral hemispheres of vertebrates. It is c ...
and
bed nucleus of the stria terminalis
The stria terminalis (or terminal stria) is a structure in the brain consisting of a band of fibers running along the lateral margin of the ventricular surface of the thalamus. Serving as a major output pathway of the amygdala, the stria termina ...
, which in turn project to the
anterior hypothalamus. These structures constitute the
accessory olfactory system.
The VNO triggers the
flehmen response in some mammals, which helps direct liquid organic chemicals to the organ. The VNO was discovered by
Frederik Ruysch prior to 1732, and later by
Ludwig Jacobson
Ludwig Lewin Jacobson (10 January 1783 – 29 August 1843) was a Denmark, Danish surgeon.
Early life
Born in Copenhagen to a Jewish family, he received his early education at the German Lyceum in Stockholm, Sweden, but on deciding to pursue the ...
in 1813.
[Jacobson, L. (1813). Anatomisk Beskrivelse over et nyt Organ i Huusdyrenes Næse. Veterinær=Selskapets Skrifter n Danish2,209–246.]
Structure
The organ
The VNO is found at the base of the
nasal cavity
The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nas ...
. It is split into two, being divided by the nasal septum, with both sides possessing an elongated C-shaped, or crescent,
lumen. It is encompassed inside a bony or cartilaginous capsule which opens into the base of the nasal cavity.
The system
The vomeronasal receptor neurons possess
axon
An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences) is a long, slender cellular extensions, projection of a nerve cell, or neuron, ...
s which travel from the VNO to the
accessory olfactory bulb (AOB), also known as the vomeronasal bulb. These sensory receptors are located on the medial concave surface of the crescent lumen. The lateral, convex surface of the lumen is covered with non-sensory ciliated cells, where the basal cells are also found. At the dorsal and ventral aspect of the lumen are vomeronasal glands, which fill the vomeronasal lumen with fluid. Sitting next to the lumen are blood vessels that dilate or constrict, forming a vascular pump that deliver stimuli to the lumen. A thin duct, which opens onto the floor of the nasal cavity inside the
nostril
A nostril (or naris , : nares ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbinates ...
, is the only way of access for stimulus chemicals.
During embryological development, the vomeronasal sensory neurons form from the nasal (olfactory)
placode
In embryology, a neurogenic placode is an area of thickening of the epithelium in the embryonic head ectoderm layer that gives rise to neurons and other structures of the sensory nervous system.
Placodes are embryonic structures that give rise t ...
, at the anterior edge of the neural plate (
cranial nerve zero
The terminal nerve, also known as cranial nerve zero or simply as CN 0, is a nerve that was not included in the seminal classification of the cranial nerves as CN I through CN XII, but has since been recognized and listed in Terminologia Anatomic ...
).
Sensory epithelium and receptors
The VNO is a tubular crescent shape and split into two pairs, separated by the
nasal septum
The nasal septum () separates the left and right airways of the Human nose, nasal cavity, dividing the two nostrils.
It is Depression (kinesiology), depressed by the depressor septi nasi muscle.
Structure
The fleshy external end of the nasal s ...
. The medial, concave area of the lumen is lined with a pseudo stratified
epithelium
Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...
that has three main cell types: receptor cells, supporting cells, and basal cells. The supporting cells are located superficially on the membrane while the basal cells are found on the basement membrane near the non-
sensory epithelium. The receptor neurons possess apical
microvilli
Microvilli (: microvillus) are microscopic cellular membrane protrusions that increase the surface area for diffusion and minimize any increase in volume, and are involved in a wide variety of functions, including absorption, secretion, cellula ...
, to which the sensory receptors are localized. These are
G-protein-coupled receptor
G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large protein family, group of evoluti ...
s, which are often referred to as
pheromone
A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...
receptors since vomeronasal receptors have been tied to detecting pheromones.
Three G-protein-coupled receptors have been identified in the VNO, each found in distinct regions: the V1Rs, V2Rs, and FPRs. V1Rs, V2Rs and FPRs are seven transmembrane receptors which are not closely related to odorant receptors expressed in the main olfactory neuroepithelium.
* V1 receptors, V1Rs, are linked to the G protein,
Gαi2. The benefit of the GPCR is that they signal in more than one direction. V1Rs are located on the apical compartment of the VNO and a relatively short
NH2-terminal
The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the amin ...
and have a great sequence diversity in their
transmembrane domain
A transmembrane domain (TMD, TM domain) is a membrane-spanning protein domain. TMDs may consist of one or several alpha-helices or a transmembrane beta barrel. Because the interior of the lipid bilayer is hydrophobic, the amino acid residues in ...
s. V1R is specifically expressed in the rodent vomeronasal organ (VNO) and is thought to be responsible for
pheromone
A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...
reception, eliciting a signal transduction.
* V2 receptors, V2Rs, are linked to the G-protein,
Gαo. These have long extracellular NH2 terminals which are thought to be the binding domain for pheromonal molecules and are located on the basal compartment of the VNO. V2R genes can be grouped into four separate families, labelled A – D. Family C V2Rs are quite distinct from the other families, and they are expressed in most basal neurons of the VNO.
The vomeronasal organ's sensory neurons act on a different signaling pathway than that of the main olfactory system's sensory neurons. Activation of the receptors stimulates
phospholipase C
Phospholipase C (PLC) is a class of membrane-associated enzymes that cleave phospholipids just before the phosphate group (see figure). It is most commonly taken to be synonymous with the human forms of this enzyme, which play an important role i ...
, which in turn opens the ion channel
TRPC2.
Upon stimulation activated by pheromones,
IP3 production has been shown to increase in VNO membranes in many animals, while adenylyl cyclase and
cyclic adenosine monophosphate
Cyclic adenosine monophosphate (cAMP, cyclic AMP, or 3',5'-cyclic adenosine monophosphate) is a second messenger, or cellular signal occurring within cells, that is important in many biological processes. cAMP is a derivative of adenosine tri ...
(cAMP), the major signaling transduction molecules of the main olfactory system, remain unaltered. This trend has been shown in many animals, such as the
hamster
Hamsters are rodents (order Rodentia) belonging to the subfamily Cricetinae, which contains 19 species classified in seven genera. They have become established as popular small pets. The best-known species of hamster is the golden or Syrian ...
, the
pig
The pig (''Sus domesticus''), also called swine (: swine) or hog, is an omnivorous, domesticated, even-toed, hoofed mammal. It is named the domestic pig when distinguishing it from other members of the genus '' Sus''. Some authorities cons ...
, the
rat
Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include '' Neotoma'' (pack rats), '' Bandicota'' (bandicoo ...
, and the
garter snake
Garter snake is the common name for small to medium-sized snakes belonging to the genus ''Thamnophis'' in the Family (biology), family Colubridae. They are native to North America, North and Central America, ranging from central Canada in the no ...
upon introduction of vaginal or seminal secretions into the environment.
V1Rs and V2Rs are activated by distinct ligands or pheromones.
*
Gi proteins are activated upon stimulation with
lipophilic
Lipophilicity (from Greek language, Greek λίπος "fat" and :wikt:φίλος, φίλος "friendly") is the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such compounds are c ...
odorants.
* Go proteins are activated by nonvolatile proteins, such as the
major urinary proteins
Major urinary proteins (Mups), also known as α2u-globulins, are a protein subfamily, subfamily of proteins found in abundance in the urine and other secretions of many animals. Mups provide a small range of identifying information about the don ...
in mice
and exocrine gland-secreting peptide 1 (ESP1).
Many vomeronasal neurons are activated by chemicals in urine. Some of the active compounds are sulfated
steroids
A steroid is an organic compound with four fused rings (designated A, B, C, and D) arranged in a specific molecular configuration.
Steroids have two principal biological functions: as important components of cell membranes that alter mem ...
. Detecting the types and amounts of different sulfated steroids conveys information about the urine donor's physiological state, and may therefore serve as an
honest signal
Within evolutionary biology, signalling theory is a body of theoretical work examining communication between individuals, both within species and across species. The central question is how organisms with conflicting interests, such as in se ...
.
Recent studies proved a new family of
formyl peptide receptor like proteins in VNO membranes of mice, which points to a close phylogenetic relation of signaling mechanisms used in olfaction and
chemosensors.
Sensory neurons
Vomeronasal sensory neurons are extremely sensitive and fire action potentials at currents as low as 1 p
A. Many patch-clamp recordings have confirmed the sensitivity of the vomeronasal neurons. This sensitivity is tied to the fact that the
resting potential
The relatively static membrane potential of quiescent cells is called the resting membrane potential (or resting voltage), as opposed to the specific dynamic electrochemical phenomena called action potential and graded membrane potential. The re ...
of the vomeronasal neurons is relatively close to that of the firing threshold of these neurons. Vomeronasal sensory neurons also show remarkably slow adaptation and the firing rate increases with increasing current up to 10 pA. The main olfactory sensory neurons fire single burst action potentials and show a much quicker adaptation rate. Activating neurons that have V1 receptors, V1Rs, cause field potentials that have weak, fluctuating responses that are seen the anterior of the accessory olfactory bulb, AOB. Activation of neurons that contain V2 receptors, V2Rs, however, promote distinct oscillations in the posterior of the AOB.
Function
Sensory neurons of the vomeronasal organ detect non-volatile chemical cues which requires direct physical contact with the source of odor but can also detect volatile compounds. Notably, some scents act as chemical-communication signals (
pheromone
A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...
s, allomones and kairomones) from other individuals of the same or from other species. Unlike sensory neurons from the main olfactory epithelium which project to the main olfactory bulb that then sends neuronal signals to the olfactory cortex, the VNO sends neuronal signals to the accessory olfactory bulb and then to the
amygdala
The amygdala (; : amygdalae or amygdalas; also '; Latin from Greek language, Greek, , ', 'almond', 'tonsil') is a paired nucleus (neuroanatomy), nuclear complex present in the Cerebral hemisphere, cerebral hemispheres of vertebrates. It is c ...
,
BNST, and ultimately
hypothalamus
The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...
. Since the hypothalamus is a major neuroendocrine center (affecting aspects of reproductive physiology and behavior as well as other functions such as body temperature), this may explain how scents influence aggressive and mating behavior. For example, in many vertebrates, nerve signals from the brain pass sensory information to the hypothalamus about seasonal changes and the availability of a mate. In turn, the hypothalamus regulates the release of reproductive hormones required for breeding. Some
pheromones
A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavi ...
are detected by the main
olfactory system
The olfactory system, is the sensory nervous system, sensory system used for the sense of smell (olfaction). Olfaction is one of the special senses directly associated with specific organs. Most mammals and reptiles have a main olfactory system ...
.
In animals
The vomeronasal organ originated in
tetrapods
A tetrapod (; from Ancient Greek τετρα- ''(tetra-)'' 'four' and πούς ''(poús)'' 'foot') is any four- limbed vertebrate animal of the clade Tetrapoda (). Tetrapods include all extant and extinct amphibians and amniotes, with the lat ...
. The functional vomeronasal system is found in all
snake
Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...
s and
lizard
Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...
s, and many
mammal
A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...
s.
*
Mice
A mouse (: mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...
use their vomeronasal organ to interact with peers, detect predators, and identify and avoid sick conspecifics.
*
Salamander
Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All t ...
s perform a nose-tapping behavior to presumably activate their VNO.
* The organ is well developed in
strepsirrhine
Strepsirrhini or Strepsirhini (; ) is a suborder of primates that includes the lemuriform primates, which consist of the lemurs of Madagascar, galagos ("bushbabies") and pottos from Africa, and the lorises from India and Southeast Asia. Colle ...
primate
Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...
s such as
lemur
Lemurs ( ; from Latin ) are Strepsirrhini, wet-nosed primates of the Superfamily (biology), superfamily Lemuroidea ( ), divided into 8 Family (biology), families and consisting of 15 genera and around 100 existing species. They are Endemism, ...
s and
loris
Loris is the common name for the strepsirrhine mammals of the subfamily Lorinae (sometimes spelled Lorisinae) in the family Lorisidae. ''Loris'' is one genus in this subfamily and includes the slender lorises, ''Nycticebus'' is the genus cont ...
es,
developed to varying degrees in
New World monkey
New World monkeys are the five families of primates that are found in the tropical regions of Mexico, Central and South America: Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae. The five families are ranked together as the Ceboi ...
s, and underdeveloped in
Old World monkey
Old World monkeys are primates in the family Cercopithecidae (). Twenty-four genera and 138 species are recognized, making it the largest primate family. Old World monkey genera include baboons (genus '' Papio''), red colobus (genus '' Piliocolob ...
s and
ape
Apes (collectively Hominoidea ) are a superfamily of Old World simians native to sub-Saharan Africa and Southeast Asia (though they were more widespread in Africa, most of Asia, and Europe in prehistory, and counting humans are found global ...
s.
*
Elephant
Elephants are the largest living land animals. Three living species are currently recognised: the African bush elephant ('' Loxodonta africana''), the African forest elephant (''L. cyclotis''), and the Asian elephant ('' Elephas maximus ...
s transfer chemosensory stimuli to the vomeronasal opening in the roof of their mouths using the
prehensile
Prehensility is the quality of an appendage or organ that has adapted for grasping or holding. The word is derived from the Latin term ''prehendere'', meaning "to grasp". The ability to grasp is likely derived from a number of different origin ...
structure, sometimes called a ''finger'', at the tips of their trunks.
*
Painted turtle
The painted turtle (''Chrysemys picta'') is the most widespread native turtle of North America. It lives in relatively slow-moving fresh waters, from southern Canada to northern Mexico, and from the Atlantic to the Pacific. They have been shown ...
s use this organ to use their sense of smell underwater.
*
Snake
Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...
s use this organ to sense prey, sticking their tongue out to gather scents and touching it to the opening of the organ when the tongue is retracted.
Garter snake
Garter snake is the common name for small to medium-sized snakes belonging to the genus ''Thamnophis'' in the Family (biology), family Colubridae. They are native to North America, North and Central America, ranging from central Canada in the no ...
s also use the vomeronasal organ in pheromone communication. Odors and vomodors should be distinguished. Odors are chemicals detected by the sensory cells in the nasal epithelium through the process of
olfaction
The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste.
In humans, ...
. Vomodors are chemicals detected by the sensory cells from the vomeronasal organ through the process of vomerolfaction. Entering the lumen, molecules contact the sensory cells attached to the neurosensory epithelium of the vomeronasal organ. The vomeronasal organ is vital to Garter snakes' perception of airborne prey odors; snakes with vomeronasal nerves cut responded to nonprey odors only.
* Bats— The vomeronasal organ is non-functional in the whole suborder Yinpterochiroptera. In the other suborder of bats, Yangochiroptera, only two families have retained function of the VNO (Phyllostomidae and Miniopteridae).
* Birds— The VNO is absent in all birds
In some other mammals the entire organ contracts or pumps in order to draw in the scents.
Flehmen response
Some mammals, particularly
felid
Felidae ( ) is the Family (biology), family of mammals in the Order (biology), order Carnivora colloquially referred to as cats. A member of this family is also called a felid ( ).
The 41 extant taxon, extant Felidae species exhibit the gre ...
s (cats) and
ungulates
Ungulates ( ) are members of the diverse clade Euungulata ("true ungulates"), which primarily consists of large mammals with hooves. Once part of the clade "Ungulata" along with the clade Paenungulata, "Ungulata" has since been determined to b ...
(which includes horses, cattle, and pigs among other species), use a distinctive facial movement called the
flehmen response to direct inhaled compounds to the VNO. The animal lifts its head after finding the odorant, wrinkles its nose while lifting its lips, and ceases to breathe momentarily.
Flehmen behavior is associated with "anatomical specialization", and animals that present flehmen behavior have
incisive papilla and ducts, which connect the oral cavity to the VNO, that are found behind their teeth. However,
horse
The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 mi ...
s are the exception: they exhibit flehmen response but do not have an incisive duct communication between the nasal and the oral cavity because they do not breathe through their mouths; instead, the VNOs connect to the nasal passages by the
nasopalatine duct.
Cats use their vomeronasal organ when
scent rubbing
Scent rubbing is a behavior where a mammal rubs its body against an object in their environment, sometimes in ones covered with strongly odored substances. It is typically shown in carnivores, although many mammals exhibit this behavior. Lowering ...
; they are able to discriminate between similar smelling substances using this organ, and then perform the rubbing behaviour.
Evidence for existence in humans
Many studies have tried to determine whether there is a VNO in adult human beings. Trotier ''et al.'' estimated that around 92% of their subjects that had no
septal surgery had at least one intact VNO. Kjaer and Fisher Hansen, on the other hand, stated that the VNO structure disappears during
fetal development
Prenatal development () involves the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal deve ...
as it does for some
primate
Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...
s. However, Smith and Bhatnagar (2000) asserted that Kjaer and Fisher Hansen simply missed the structure in older fetuses. Won (2000) found evidence of a VNO in 13 of his 22 cadavers (59.1%) and 22 of his 78 living patients (28.2%). In a study using retrospective analysis of nearly one thousand outpatient nasal endoscopies, Stoyanov et al. (2016) found the organ to be present in 26.83% of the Bulgarian population.
Given these findings, some scientists have argued that there is a VNO in adult human beings. However, most investigators have sought to identify the opening of the VNO in humans, rather than identify the tubular
epithelial
Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...
structure itself.
Thus it has been argued that such studies, employing macroscopic observational methods, have sometimes misidentified or even missed the vomeronasal organ.
Among studies that use
microanatomical methods, there is no reported evidence that human beings have active sensory neurons like those in working vomeronasal systems of other animals. Furthermore, there is no evidence to date that suggests there are nerve and axon connections between any existing sensory receptor cells that may be in the adult human VNO and the brain. Likewise, there is no evidence for any accessory olfactory bulb in adult human beings,
and the key genes involved in VNO function in other mammals have
pseudogenized in human beings. Therefore, while many debate the structure's presence in adult human beings, a review of the scientific literature by Tristram Wyatt concluded that on current evidence, "most in the field... are skeptical about the likelihood of a functional VNO in adult human beings."
[Wyatt, Tristram D. (2003). ''Pheromones and Animal Behaviour: Communication by Smell and Taste.'' Cambridge: Cambridge University Press. . p295]
History
The VNO was discovered by
Frederik Ruysch prior to 1732, and later by
Ludwig Jacobson
Ludwig Lewin Jacobson (10 January 1783 – 29 August 1843) was a Denmark, Danish surgeon.
Early life
Born in Copenhagen to a Jewish family, he received his early education at the German Lyceum in Stockholm, Sweden, but on deciding to pursue the ...
in 1813.
References
Further reading
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{{DEFAULTSORT:Vomeronasal Organ
Olfactory system
Vertebrate anatomy
Pheromones
Vestigial organs