Odor
Odorous molecules bind to receptor proteins extending from cilia and act as a chemical stimulus, initiating electric signals that travel along the olfactory nerve's axons to the brain.
[citation needed] Experienced individuals, however, such as flavorists and perfumers, can identify discrete chemicals in complex mixtures using only their sense of smell.
Humans have an unusually good sense of smell considering they have only 350 functional olfactory receptor genes compared to the 1,300 found in mice, for example.
The sensitivity and ability to discriminate odors diminishes with exposure, and the brain tends to ignore continuous stimulus and focus on differences and changes in a particular sensation.
[19] In 2012, Zhuang, Matsunami, and Block confirmed the Crabtree/Suslick proposal for the specific case of a mouse OR, MOR244-3, showing that copper is essential for detection of certain thiols and other sulfur-containing compounds.
However, these authors also found that MOR244-3 lacks the specific metal ion binding site suggested by Suslick, instead showing a different motif in the EC2 domain.
The perception of an odor may change from pleasant to unpleasant with increasing concentration, intensity, time, frequency, or previous experience with a specific odor—all factors in determining a response.
Percentiles refer to a statistical representation of how many hours per year the concentration C may be exceeded based on the averaging period.
Direct refers to the placement of an enclosure on or over an emitting surface from which samples are collected, and an odor emission rate is determined.
The most commonly used direct methods include the flux chamber[37] and wind tunnels such as the one at the University of New South Wales (UNSW).
Some inhaled chemicals are volatile compounds that act as a stimulus, triggering unwanted reactions such as nose, eye, and throat irritation.
Perception of odor and of irritation is unique to each person, and varies because of physical conditions or memory of past exposures to similar chemicals.
Health effects and symptoms vary—including eye, nose, or throat irritation, cough, chest tightness, drowsiness, and mood change—all of which decrease as an odor ceases.
Some believe that these messages have the power to alter moods, evoke distant memories, raise spirits, and boost self-confidence.
This belief has led to "aromatherapy", wherein fragrances are claimed to cure a wide range of psychological and physical problems.
Aromatherapy claims that fragrances can positively affect sleep, stress, alertness, social interaction, and general feelings of well-being.
To help users detect leaks, an odorizer with the scent of rotten eggs, tert-Butylthiol (t-butyl mercaptan), is added.
[42] Unpleasant odors can arise from specific industrial processes, adversely affecting workers and even residents downwind of the source.
Body odor is present both in animals and humans and its intensity can be influenced by many factors (behavioral patterns, survival strategies).
According to a 2006 study, this smell is the result of aldehydes (for example, nonanal) and ketones: 1-octen-3-one) released from the human skin on contact with ferrous ions that are formed in the sweat-mediated corrosion of iron.
[47][48] Odor perception is a complex process involving the central nervous system and can evoke psychological and physiological responses.
[49] Odors can disturb our concentration, diminish productivity, evoke symptoms, and in general increase a dislike for an environment.
[53] Human body odors influence interpersonal relationships and are involved in adaptive behaviors, such as parental attachment in infants or partner choice in adults.
Biologically females tend to select mates "who are most likely to secure offspring survival and thus increase the likelihood that her genetic contribution will be reproductively viable.
Using a brain-imaging technique, Swedish researchers have shown that gay and straight males' brains respond in different ways to two odors that may be involved in sexual arousal, and that the gay men respond in the same way as straight women, though it could not be determined whether this was cause or effect.
For example, "technicians at New York City’s Sloan-Kettering Cancer Center disperse vanilla-scented oil into the air to help patients cope with the claustrophobic effects of MRI testing.
Without perfume or aftershave, humans unconsciously detect people's natural scents: in the form of pheromones.
According to the heterozygotes-advantage hypothesis, diversity within the MHC genotype is beneficial for the immune system due to a greater range of antigens available to the host.
[73] It has also been found that women were reminded more of current or prior partners when smelling odors from men whose MHC was dissimilar to their own.
[76] The ovulatory-shift hypothesis argues that women experience elevated immediate sexual attraction, relative to low-fertile days of the cycle, to men with characteristics that reflect good genetic quality.
