UCI Psych 160D (Brain Disorders) - Unit 5b: Gustation (Taste)

Tastant molecule

any substance capable of stimulating the sense of taste

Taste receptor cells

provide taste information; they are located throughout the tongue in the taste buds, have areas of higher sensitivity, and have a very short life span (i.e., they are replaced frequently with new taste cells)

Taste bud

structure on the tongue that contains several taste receptor cells; a young tongue contains ~10,000 taste buds

Microvilli

microscopic cellular membrane protrusions that increase the surface area of cells and minimize any increase in volume and are involved in a wide variety of functions

Taste pore

any of numerous spherical clusters of receptor cells found mainly in the epithelium of the tongue and constituting the end organs of the sense of taste

Papillae

the majority of taste buds on the tongue sit on raised protrusions of the tongue surface called papillae (papilla = singular form / papillae = plural form); there are four types of papillae present in the human tongue; these types differ by shape, location on tongue, and location of taste buds within a papilla

Filiform papillae

these are thin, long papillae "V"-shaped cones that don't contain taste buds but are the most numerous; these papillae are mechanical and not involved in gustation

Fungiform papillae

as the name suggests, these are slightly mushroom-shaped if looked at in section; these are present mostly at the apex (tip) of the tongue, as well as at the sides

Foliate papillae

these are ridges and grooves towards the posterior part of the tongue found on lateral margins

Circumvallate papillae

there are only about 3-14 of these papillae on most people, and they are present at the back of the oral part of the tongue; they are arranged in a circular-shaped row just in front of the sulcus terminalis of the tongue

Supertasters

people who have a genetic mutation producing extra fungiform papillae and an increase of gustatory nerve fibers per papilla; they therefore experience a greater intensity of taste than normal, and may be especially sensitive to bitter tastes and the texture of fat

Gustatory nerves

nerve fibers at each taste bud that receive information from the taste receptor cells; their axons join three different cranial nerves to carry taste information to cortex (which cranial nerve depends on location in tongue and pharynx/throat)

Anterior insula & frontal operculum

adjacent cortical regions involved in taste processing; considered to be primary gustatory cortex; plays a primary role in taste identification and evaluation of taste intensity

Orbitofrontal cortex for taste

ventral region of the frontal lobes that is located just above the orbits of the eyes; contains secondary gustatory cortex (among other functions; see above for olfaction), which is involved in identifying taste, determining the reward value (e.g., pleasantness) of a taste, combining multisensory information to determine flavor, and signaling satiety (fullness)

Flavor

the perception of flavor is a multisensory experience, which relies on the integration of cues from most of the human senses; the process of flavor perception involves the complex interaction of taste with the smell, texture (from S1), and sight of food; in addition, flavor perception changes over time during a meal to signal satiety or fullness

Ageusia

the complete loss of taste; patients will not be able to discriminate differences among sweetness, sourness, bitterness, saltiness, and umami

Hypogeusia

partial loss of taste; taste sensitivity is reduced

Dysgeusia

distortion or alteration of taste; food tastes abnormal

Causes of ageusia, hypogeusia, dysgeusia

medication side effects, vitamin deficiencies, and respiratory illnesses with clogged nasal sinuses are common causes of dysgeusia and hypogeusia; trauma is a common cause of ageusia

Geographical tongue

an inflammatory condition of the mucous membrane of the tongue in which the loss of fungiform papillae produce smooth, red, painful regions that change location over time; may result from other infections or medications like antibiotics

Fissured tongue

benign condition characterized by deep grooves (fissures) in the top surface of the tongue; associated with geographical tongue, aging, environmental factors, and genetic conditions like Down's syndrome