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Olfaction, also known as olfactics,[1] is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, which can be considered analogous to sensory cells of the antennae of invertebrates.

In humans, olfaction occurs when odorant molecules bind to specific sites on the olfactory receptors. These receptors are used to detect the presence of smell. They come together at the glomerulus, a structure which transmits signals to the olfactory bulb (a brain structure directly above the nasal cavity and below the frontal lobe).[2] Many vertebrates, including most mammals and reptiles, have two distinct olfactory systems—the main olfactory system, and the accessory olfactory system (used mainly to detect pheromones). For air-breathing animals, the main olfactory system detects volatile chemicals, and the accessory olfactory system detects fluid-phase chemicals.[3] Olfaction, along with taste, is a form of chemoreception. The chemicals themselves that activate the olfactory system, in general at very low concentrations, are called odorants. Although taste and smell are separate sensory systems in land animals, water-dwelling organisms often have one chemical sense.[4]

Volatile small molecule odorants, non-volatile proteins, and non-volatile hydrocarbons may all produce olfactory sensations. Some animal species are able to smell carbon dioxide in minute concentrations.

Olfaction. Volatile small molecule odorants, non-volatile proteins, and non-volatile hydrocarbons may all produce olfactory sensations.


Some animal species are able to smell carbon dioxide in minute concentrations.[5] Study of olfaction[edit] Study of Olfaction.

Main Olfactory system

Assessor you olfactory system. Human olfactory system. Body odor. Body odor or body odour or BO is present in animals and humans, and its intensity can be influenced by many factors (behavioural patterns, survival strategies).

Body odor

Body odor has a strong genetic basis both in animals and humans, but it can be also strongly influenced by various diseases and psychological conditions. Body odor is considered an unpleasant odor among many human cultures. Causes[edit] Olfactory coding and perception. Genetics of olfaction.

Interaction of olfaction with other senses

Disorders of Smell. Quantifying olfaction in industry. Olfaction in plants and animals. Insect olfactory system. Scent transfer unit. A scent transfer unit is a vacuum device used to collect scent evidence from a crime scene or item of evidence.[1] The unit was invented by Bill Tolhurst (a former president of the National Police Bloodhound Association) while working for the Niagara County Sheriff's Department.[2] Several law enforcement agencies have bought scent transfer units.

Scent transfer unit

Although the reliability of scent evidence in general has been called into question, certain experiments have demonstrated successful use of scent transfer units.[2][3] ^ Jump up to: a b Hess, Karen M. (2009). Criminal Investigation. Olfactory fatigue. Olfactory fatigue, also known as odor fatigue or olfactory adaptation, is the temporary, normal inability to distinguish a particular odor after a prolonged exposure to that airborne compound.[1] For example, when entering a restaurant initially the odor of food is often perceived as being very strong, but after time the awareness of the odor normally fades to the point where the smell is not perceptible or is much weaker.

Olfactory fatigue

After leaving the area of high odor, the sensitivity is restored with time. Perfume counters will often have containers of coffee beans which tend to "reset" olfaction. Olfactory ensheathing glia. Olfactory ensheathing glia (OEG), also known as olfactory ensheathing cells (OECs) or olfactory ensheathing glial cells, are a type of macroglia (radial glia) found in the nervous system.

Olfactory ensheathing glia

They are also known as olfactory Schwann cells because they ensheath the non-myelinated axons of olfactory neurons in a similar way to which Schwann cells ensheath non-myelinated peripheral neurons. They also share the property of assisting axonal regeneration. Olfactometer. An olfactometer is an instrument used to detect and measure odor dilution.


Olfactometers are used in conjunction with human subjects in laboratory settings, most often in market research, to quantify and qualify human olfaction.[1] Olfactometers are used to gauge the odor detection threshold of substances. To measure intensity, olfactometers introduce an odorous gas as a baseline against which other odors are compared. Many scientists use the term "olfactometer" to refer to a device used to study insect behavior in presence of an olfactory stimulus. It consists of a tube with a bifurcation (with "T" or "Y" shape) where an insect walks and decides between two choices, usually clean air versus air carrying an odor. Odor. An odor or odour or fragrance is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction.


Odors are also commonly called scents, which can refer to both pleasant and unpleasant odors. The terms fragrance and aroma are used primarily by the food and cosmetic industry to describe a pleasant odor, and are sometimes used to refer to perfumes. In contrast, malodor, stench, reek, and stink are used specifically to describe unpleasant odor. In the United Kingdom, odour refers to scents in general. In the United States, odor has a more negative connotation, such as smell, stench, funk, or stink, while scent or aroma are used for pleasant smells. Nasal administration. Spiral of Ketamine for Snorting Nasal administration can be used to deliver drugs for either local or systemic effect.

Nasal administration

Locally acting drugs are for example decongestants and allergy treatments. Machine olfaction. Machine olfaction is the automated simulation of the sense of smell.

Machine olfaction

It is an emerging application of modern engineering where robots or other automated systems are needed to measure the existence of a particular chemical concentration in air. Such an apparatus is often called an electronic nose or e-nose. Machine olfaction is complicated by the fact that e-nose devices to date have had a limited number of elements, whereas each odor is produced by own unique set of (potentially numerous) odorant compounds. because[1] This technology is still in the early stages of development, but it promises many applications, such as:[2] Electronic nose. An electronic nose is a device intended to detect odors or flavors.

Electronic nose

Other techniques to analyze odors[edit] In all industries, odor assessment is usually performed by human sensory analysis, by chemosensors, or by gas chromatography. The latter technique gives information about volatile organic compounds but the correlation between analytical results and actual odor perception is not direct due to potential interactions between several odorous components.

In the Wasp Hound odor detector, the mechanical element is a video camera and the biological element is five parasitic wasps who have been conditioned to swarm in response to the presence of a specific chemical.[2] Chemesthesis. Chemesthesis is defined as the chemical sensibility of the skin and mucous membranes. Chemesthetic sensations arise when chemical compounds activate receptors associated with other senses that mediate pain, touch, and thermal perception.

These chemical-induced reactions do not fit into the traditional sense categories of taste and smell. Examples of chemesthetic sensations include the burn-like irritation from chili pepper, the coolness of menthol in mouthwashes and topical analgesic creams, the stinging or tingling of carbonation in the nose and mouth, and the tear-induction of onions.[1] Some of these sensations may be referred to as spiciness, pungency, or piquancy. Because chemoresponsive nerve fibers are present in all types of skin, chemesthetic sensations can be aroused from anywhere on the body's surface as well as from mucosal surfaces in the nose, mouth, eyes, etc.