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Smell, or olfaction, is a chemoreception that forms the sense of smell. Olfaction has many purposes, such as the detection of hazards, pheromones, and food. It integrates with other senses to form the sense of flavor. [8] Olfaction occurs when odorants bind to specific sites on olfactory receptors located in the nasal cavity. [9]
Senses and receptors [ edit ] While debate exists among neurologists as to the specific number of senses due to differing definitions of what constitutes a sense , Gautama Buddha and Aristotle classified five 'traditional' human senses which have become universally accepted: touch , taste , smell , vision , and hearing .
Receptor cells disseminate onto different neurons and convey the message of a particular taste in a single medullar nucleus. This pheromone detection system deals with taste stimuli. The pheromone detection system is distinct from the normal taste system, and is designed like the olfactory system .
The Lady and the Unicorn, a Flemish tapestry depicting the sense of smell, 1484–1500. Musée national du Moyen Âge, Paris.. Early scientific study of the sense of smell includes the extensive doctoral dissertation of Eleanor Gamble, published in 1898, which compared olfactory to other stimulus modalities, and implied that smell had a lower intensity discrimination.
Somatosensation is considered a general sense, as opposed to the special senses discussed in this section. Somatosensation is the group of sensory modalities that are associated with touch and interoception. The modalities of somatosensation include pressure, vibration, light touch, tickle, itch, temperature, pain, kinesthesia. [18]
External receptors that respond to stimuli from outside the body are called exteroreceptors. [4] Exteroreceptors include chemoreceptors such as olfactory receptors and taste receptors, photoreceptors (), thermoreceptors (temperature), nociceptors (), hair cells (hearing and balance), and a number of other different mechanoreceptors for touch and proprioception (stretch, distortion and stress).
They also sense decrease in partial pressure of O 2, but to a lesser degree than for pCO 2 and H + ion concentration. The chemoreceptor trigger zone is an area of the medulla in the brain that receives inputs from blood -borne drugs or hormones , and communicates with the vomiting center (area postrema) to induce vomiting .
Nociceptors are specialised receptors for signals of pain. [4] The sense of touch in perceiving the environment uses special sensory receptors in the skin called cutaneous receptors. They include mechanoreceptors such as tactile corpuscles that relay information about pressure and vibration; nociceptors, and thermoreceptors for temperature ...