Chapter 13 (Taste) Flashcards
Tastants
molecules that taste receptors “recognize” and respond to by producing neural signals that the brain represents as perceptions of different tastes
- Dissolve in saliva and activate taste receptor cells within taste buds,
- Different detection thresholds
Basic tastes
five well-established taste categories- sweet, salty, umami, sour and bitter
*Associated with tastants that fill particular nutritive needs
Umami
basic taste evoked by tastants such as MSG and certain amino acids found in meats; it generally signals the presence of protein in food
- Recent addition to basic taste
- Glutamate receptors in the gut may serve the protein signaling function
Flavor
total sensory experience evoked by ingesting something; it includes the perception of the basic tastes, the perception of other attributes of tastants such as pleasantness and intensity, and other sensory properties, the most important of which is smell
- Comes both from odorants released by the food before it is placed in the mouth (nasal cavity via the nostrils)
- From the odorants released while the food is in the mouth and being chewed and swallowed (nasal cavity via the retronasal pathway)
Taste buds
structures that contain taste receptor cells, within papillae in the mouth
- 3,000-12,000 taste buds on average
- A third of them on soft palate, epiglottis, and upper esophagus
- Two-thirds on the tongue, within papillae
Papillae
tiny structures on surfaces in the mouth, mainly on the tongue; three different types of papillae contain taste buds
Fungiform papillae
tiny mushroom-shaped structures located along the edges and top of the front two-thirds of the tongue, each fungiform papilla contains 3-5 taste buds on its upper surface
Foliate papillae
ridgelike folds of tissue located on the sides of the tongue near the back; a few hundred taste buds are tucked into each fold
Circumvallate papillae
mushroom-shaped structures (much larger than fungiform papillae) situated in a row at the back of the tongue; each circumvallate papilla contains 200-700 taste buds around its sides
Filiform papillae
don’t contain taste buds, cover much of the tongue’s surface; contain somatosensory receptors thought to provide information about the texture of food
*Most common
Taste receptor cells (TRCs)
elongated neurons with cilia at their outer ends and without axons, packed within taste buds, that transduce tastants into neural signals
- Each TRC lives for only a week or so and is then replaced
- New TRCs develop from basal cells in the taste buds
- The cilia of the TRCs project into a taste pore (opening onto the surface of the tongue) at the top of the taste bud, where the cilia come into contact with tastant molecules dissolved in saliva
Receptor cells
type of taste receptor cells containing receptors that initiate transduction of sweet, umami, and bitter tastants
- Each receptor cell contains only a single category of receptors on its cilia
- Do not have synapses with cranial nerve fibers
Presynaptic cells
a type of taste receptor cells in which the receptors take the form of ion channels where transduction of salty and sour tastants is initiate
* Inner ends of presynaptic cells release neurotransmitters into synapses with cranial nerve fibers that send taste signals to the brain
Cell-to-cell signaling
signals from receptor cells to presynaptic cells, causing the presynaptic cells to release neurotransmitters in a way that carries information about sweet, umami, and bitter tastes.
Labeled-line model
each cranial nerve fiber carries signals with information about just one of the five taste qualities, and that the cortical neurons on the receiving end of these signals also respond only to information about a single type of tastant.
* There is a single “labeled line” from the specialized TRCs in taste buds to correspondingly specialized cranial nerve fibers to correspondingly specialized cortical neurons.
Across-fiber pattern model
cranial nerve fibers can carry signals from multiple taste receptor types, and that the cortical neurons receiving these signals are broadly tuned to respond to signals carrying information about multiple types of tastants.
*cranial nerve fibers carry information about differences in taste quality based on the relative activity of a few different types of receptors (TIR1-TIR3, TIR2-TIR3, T2R2, and 3 different ion channels)
Facial nerve (Cranial nerve VII)
innervates the front two-thirds of the tongue and the soft palate
Glossopharyngeal nerve (Cranial nerve IX)
innervates the back one-third of the tongue
Vagus nerve (Cranial nerve X)
innervates the epiglottis and the upper esophagus
Primary taste cortex
first cortical areas to receive taste signals, consisting of the anterior insular cortex and the frontal operculum
*taste qualities; identify tastants
Orbitofrontal cortex (OFC)
Respond strongly- indicating high reward value- only when the animal is hungry.
- Motivate organisms to eat when they’re hungry
- Pleasantness of eating flavorful foods
- Receives signals not only from the primary taste cortex but also from many other sensory modalities
- Flavor, reward value
eNose
electronic nose; capable of detecting and identifying odorants, localizing their source, and even tracking odor plumes
- Sampling the chemical composition of the air in environments
- Helping diagnose diseases that often produce characteristic odors in concentrations too low for the human nose to detect and identify
- Detecting drugs or explosives
- Monitoring foods for freshness and possible contamination
Orthonasal and retronasal
From the front of the nose and from the back of the nose
- odors have different significance if they come from the mouth or from the outside world.
- Outside the world or inside your mouth
Super tasters
Experience heightened taste sensations to a broad range of tastes
- Higher density of fungiform papillae on the tongue and presumably, higher density of taste receptors
- 35% women; 15% men
- Intense sensations of oral burn, oral touch, retronasal olfaction, intense flavor (by trigeminal somatosensory nerve)
