Taste A79 Taste Physiology



Download 290.42 Kb.
Date06.02.2017
Size290.42 Kb.

taste A79 ()banner_for_pages

Taste Physiology

Last updated: April 3, 2016



taste buds (sense organs for taste) see 1826 (2-4) p.

  • total ≈ 10.000 taste buds.

  • each taste bud is innervated by ≈ 50 nerve fibers; each nerve fiber receives input from ≈ 5 taste buds.

  • if sensory nerve is cut, taste buds it innervates degenerate and eventually disappear;

if nerve regenerates, epithelial cells in neighborhood become organized into new taste buds.

Taste Pathways

Tongue:

anterior two-thirds → chorda tympani branch of facial nerve.



posterior third → glossopharyngeal nerve.

Areas other than tonguevagus nerve.


  • all taste fibers (myelinated but slowly conducting) unite in rostral third of nucleus tractus solitarii (in medulla oblongata); further way:

    1. axons cross midline and join medial lemniscus → specific sensory relay nuclei of thalamus.

    2. gustatory lemniscus - uncrossed ascending fibers; some switch in parabrachial nuclei (rostral pons) and continue to thalamus, hypothalamus, amygdala.

    3. some axons connect to adjacent RF and dorsal motor nucleus n. vagi – salivatory and lingual reflexes.

  • taste projection area is in foot of postcentral gyrus (parietal operculum).

N.B. taste does not have separate cortical projection area and is represented in face area.

d:\viktoro\neuroscience\a. neuroscience basics\a79. taste\00. pictures\central taste pathways.jpg
Basic Taste Modalities

  • gustatory chemoreceptors (located on microvilli of taste cells) respond to sapid (taste-producing) substances dissolved in oral fluids bathing them.

  • concentrating & transporting protein (delivers taste-producing molecules to receptors) is produced by Ebner glands.

sweet - at tongue tip.

  • most sweet substances are organic: sucrose, maltose, lactose, glucose, polysaccharides, glycerol, some alcohols and ketones, chloroform, beryllium salts, various amides of aspartic acid.

  • artificial sweeteners (saccharin and aspartame) produce satisfactory sweetening without calorie burden.

  • thaumatin and monellin (proteins isolated from African berries) are 100,000 times as sweet as sucrose; structures of these two proteins are very different, yet antibodies to one cross-react with antibodies to other (some sort of common 3D structure).

  • receptor activation: sweet substances act via GS protein → cAMP↑ → reduced K+ conductance → depolarization.

d:\viktoro\neuroscience\a. neuroscience basics\a79. taste\00. pictures\f-69.jpg

sour - along posterior half of tongue side (also on palate).

  • sourness is proportionate to H+ concentration.

  • receptor activation: acids depolarize sour receptors by activating H+-gated cation channels.

salt - along anterior half of tongue side.

  • salty taste is produced by Na+ (and anions of ionizable salts).

  • receptor activation: Na+ depolarizes salt receptors via Na+ channel related to amiloride-sensitive epithelial sodium channel (ENaC).

  • some organic compounds also taste salty (e.g. dipeptides lysyltaurine & ornithyltaurine are more potent than NaCl).

bitter - mostly on tongue back (also on palate).

  • no apparent common molecular feature of substances that taste bitter.

  • organic compounds (esp. alkaloids): quinine sulfate, strychnine hydrochloride, morphine, nicotine, caffeine, urea.

  • inorganic salts of magnesium, ammonium, calcium.

  • receptor activation: bitter substances reduce cAMP (via G protein*) and increase IP3 and DAG.

*novel G protein (α-gusducin) has been cloned - it activates phosphodiesterase, but exact role remains unsettled.


  • all four modalities can be sensed on pharynx and epiglottis.

  • additional taste modality named umami has been postulated to exist - taste of (monosodium) glutamate.

  • taste cells are not different histologically; each nerve fiber responds to more than one taste stimulus (but responds best to one of four primary taste qualities).

  • intensity discrimination is relatively crude (like in olfaction) - 30% change in concentration of substance being tasted is necessary before intensity difference can be detected.

  • taste threshold concentrations vary with particular substance:

d:\viktoro\neuroscience\a. neuroscience basics\a79. taste\00. pictures\taste thresholds.gif
Flavor components:

  1. combinations of four basic taste components.

  2. smell – nn. olfactorii

  3. may include element of pain stimulation (e.g. "hot" sauces) – n. trigeminus

  4. consistency (texture) – n. trigeminus

  5. temperature – n. trigeminus

N.B. taste is component of flavor!

After-Effects

  • taste exhibits after-reactions and contrast phenomena (similar to visual after-images and contrasts) - some are chemical "tricks," but others may be true central phenomena.

  • miraculin - taste modifier protein discovered in plant - when applied to tongue, makes acids taste sweet.

  • animals and humans form particularly strong aversions to novel foods if eating food is followed by illness (survival value of avoiding poisons).



Taste Abnormalities

ageusia (absence of taste sense); e.g. drugs which contain sulfhydryl groups (e.g. captopril, penicillamine) cause temporary ageusia.
hypogeusia (diminished taste sensitivity) - many different diseases.
dysgeusia (disturbed taste sense).

Bibliography for ch. “Taste” → follow this link >>

Ganong “Review of Medical Physiology”, 2002

NMS Neuroanatomy 1998, Physiology 2001

Viktor’s Notes℠ for the Neurosurgery Resident



Please visit website at www.NeurosurgeryResident.net


Directory: A.%20Neuroscience%20Basics -> A79.%20Taste
A.%20Neuroscience%20Basics -> Brain Stem Lesions A59 Brain Stem lesions
A.%20Neuroscience%20Basics -> Embryogenesis of cns blood vessels A201 Embryogenesis of cns blood vessels
A.%20Neuroscience%20Basics -> Bbb a8 Blood-brain barrier (bbb)
A.%20Neuroscience%20Basics -> Diencephalon A110 Diencephalon
A.%20Neuroscience%20Basics -> Vestibulospinal Tract
A.%20Neuroscience%20Basics -> Facial Nerve A73 Facial Nerve
A.%20Neuroscience%20Basics -> Corticonuclear (corticobulbar) fibers A55 (8) Corticonuclear (corticobulbar) fibers
A.%20Neuroscience%20Basics -> Autonomic ns pharmacology A35 Autonomic Nervous System Pharmacology
A.%20Neuroscience%20Basics -> Smell functions Warning spoiled foods, leaking natural gas, polluted air, smoke. Basic communication
A79.%20Taste -> Taste A79 Taste Physiology


Share with your friends:


The database is protected by copyright ©dentisty.org 2019
send message

    Main page