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Encyclopedia > Gustatory system

The gustatory system is the sensory system that uses taste buds (or lingual papillae) on the upper surface of the tongue to provide information about the taste of food being eaten. This article or section may be confusing for some readers, and should be edited to be clearer or more simplified. ... Taste buds are small structures on the upper surface of the tongue, soft palate, and epiglottis that provide information about the taste of food being eaten. ... This page is a candidate to be moved to Wiktionary. ... An open surface with X-, Y-, and Z-contours shown. ... This article includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ... The ASCII codes for the word Wikipedia represented in binary, the numeral system most commonly used for encoding computer information. ... For the pop music band, see The The. ... Taste is one of the traditional five senses and refers to the ability to detect the flavor of foodstuffs and other substances (e. ... A meal is an instance of eating, specifically one that takes place at a specific time and includes specific, prepared foodstuffs. ...

Contents

Importance

Humans, as a living organism, require nutrition like any other organism. As such, they also require a way to distinguish between safe food items and dangerous food items. This ability has evolved into us as a species, and has resulted in the pleasure and displeasure we feel when eating certain foods. Bitter and sour foods we find unpleasant, while salty, sweet, and meaty tasting foods generally provide a pleasurable sensation. The five specific tastes received by gustatory receptors are salty, sweet, bitter, sour, and umami, which means “savory” in Japanese. Human beings are defined variously in biological, spiritual, and cultural terms, or in combinations thereof. ... This article or section does not cite any references or sources. ... The updated USDA food pyramid, published in 2005, is a general nutrition guide for recommended food consumption. ... The Other or constitutive other (also referred to as othering) is a key concept in continental philosophy, opposed to the Same. ... This article is about evolution in biology. ... Bitter can refer to: Bitter, one of the five basic tastes; Bitter, a kind of ale particularly popular in Britain or Bitters, a herbal preparation now used mostly in cocktails. ... Human taste sensory organs, called taste buds or gustatory calyculi, and concentrated on the upper surface of the tongue, appear to be receptive to relatively few chemical species as tastes. ... Human taste sensory organs, called taste buds or gustatory calyculi, and concentrated on the upper surface of the tongue, appear to be receptive to relatively few chemical species as tastes. ... Look up Sweet in Wiktionary, the free dictionary. ... Human taste sensory organs, called taste buds or gustatory calyculi, and concentrated on the upper surface of the tongue, appear to be receptive to relatively few chemical species as tastes. ...


According to Lindemann, both salt and sour taste mechanisms detect, in different ways, the presence of sodium chloride in the mouth. The detection of salt is important to many organisms, but specifically mammals, as it serves a critical role in ion and water homeostasis in the body. It is specifically needed in the mammalian kidney as an osmotically-active compound which facilitates passive re-uptake of water into the blood. Because of this, salt elicits a pleasant response in most humans. Homeostasis is the property of an open system, especially living organisms, to regulate its internal environment to maintain a stable, constant condition, by means of multiple dynamic equilibrium adjustments, controlled by interrelated regulation mechanisms. ... The kidneys filter wastes (such as urea) from the blood and excrete them, along with water, as urine. ...


Sour taste can be mildly pleasant in small quantities, as it is linked to the salt flavour, but in larger quantities it becomes more and more unpleasant to taste. This is because the sour taste can signal over-ripe fruit, rotten meat, and other spoiled foods, which can be dangerous to the body because of bacteria which grow in such mediums. As well, sour taste signals acids (H+ ions), which can cause serious tissue damage. For alternative meanings see acid (disambiguation). ...


The bitter taste is almost completely unpleasant to humans. This is because many nitrogenous organic molecules which have a pharmacological effect on humans taste bitter. These include caffeine, nicotine, and strychnine, which compose the stimulant in coffee, addictive agent in cigarettes, and active compound in many pesticides, respectively. It is interesting to note that many common medicines have a bitter taste if chewed; this is because most medicines are poisons taken in controlled doses. In this manner, the unpleasant reaction to the bitter taste is a last-line warning system before the compound is ingested and can do damage. Caffeine is a xanthine alkaloid compound that acts as a stimulant in humans. ... Nicotine is an alkaloid found in the nightshade family of plants (Solanaceae), predominantly in tobacco, and in lower quantities in tomato, potato, eggplant (aubergine), and green pepper. ... Strychnine (pronounced (British) or (U.S.)) is a very toxic (LD50 = 10 mg approx. ... A cup of coffee Workers sorting and pulping coffee beans in Guatemala Coffee is a widely consumed beverage prepared from the roasted seeds — commonly referred to as beans — of the coffee plant. ... A cigarette will burn to ash on one end. ... the plane is spreading pesticide. ...


Sweet taste signals the presence of carbohydrates in solution. Since carbohydrates have a very high calorie count (saccharides have many bonds, therefore much energy), they are desirable to the human body, which has evolved to seek out the highest calorie intake foods, as the human body in the distant past has never known when its next meal will occur. They are used as direct energy (sugars) and storage of energy (glycogen). However, there are many non-carbohydrate molecules that trigger a sweet response, leading to the development of many artificial sweeteners, including saccharin, sucralose, and aspartame. This probably does not mean that this particular taste receiver has very ambiguous criteria, or is “easily fooled”, but rather that our understanding of the system and its evolutionary significance is still fledgling. Carbohydrates (literally hydrates of carbon) are chemical compounds that act as the primary biological means of storing or consuming energy, other forms being fat and protein. ... This article deals with sugar as food and as an important, widely traded commodity; the word also has other uses; see Sugar (disambiguation) A sugar is a form of carbohydrate; the most commonly used sugar is a white crystalline solid, sucrose; used to alter the flavor and properties (mouthfeel, perservation... Electron micrograph of a section of a liver cell showing glycogen deposits as accumulations of electron dense particles (arrows). ... The skeletal formula of saccharin Saccharin is the oldest artificial sweetener; it was discovered in 1879 by Ira Remsen and Constantin Fahlberg of Johns Hopkins University. ... Sucralose is an artificial sweetener known by the trade name Splenda and the generic Altern. ... Aspartame (IPA: ) is the name for an artificial, non-carbohydrate sweetener, aspartyl-phenylalanine-1-methyl ester; i. ...


The umami taste, which signals the presence of the amino acid L-glutamate, triggers a pleasurable response and thus encourages the intake of peptides and proteins. The amino acids in proteins are used in the body to build muscles and organs, transport molecules (hemoglobin), antibodies, and the organic catalysts known as enzymes. These are all critical molecules, and as such it is important to have a steady supply of amino acids, hence the pleasurable response to their presence in the mouth. Human taste sensory organs, called taste buds or gustatory calyculi, and concentrated on the upper surface of the tongue, appear to be receptive to relatively few chemical species as tastes. ... Phenylalanine is one of the standard amino acids. ... Glutamic acid (Glu, E), also referred to as glutamate (the anion), is one of the 20 proteinogenic amino acids. ... Peptides are the family of molecules formed from the linking, in a defined order, of various amino acids. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... 3-dimensional structure of hemoglobin. ... Wikipedia does not yet have an article with this exact name. ... Neuraminidase ribbon diagram An enzyme (in Greek en = in and zyme = blend) is a protein, or protein complex, that catalyzes a chemical reaction and also controls the 3D orientation of the catalyzed substrates. ...


Function

In the human body a stimulus refers to a form of energy which elicits a physiological or psychological action or response. Sensory receptors are the structures in the body which change the stimulus from one form of energy to another. This can mean changing the presence of a chemical, sound wave, source of heat, or touch to the skin into an electrical “action potential” which can be understood by the brain, the body’s control center. Sensory receptors are modified ends of sensory neurons; modified to deal with specific types of stimulus, thus there are many different types of sensory receptors in the body. The neuron is the primary component of the nervous system, which transmits messages from sensory receptors all over the body. Look up stimulus in Wiktionary, the free dictionary. ... In a sensory system, a sensory receptor is a structure that recognizes a stimulus in the internal or external environment of an organism. ... Neurons (also called nerve cells) are the primary cells of the nervous system. ...


The Neuron

A typical neuron has all the parts an ordinary cell would have, as well as a few which set it apart. The main part of the cell is known as the soma or cell body, which contains the nucleus. Spreading out from the soma are a number of arms known as dendrites, where the neuron receives its message from. A long arm known as the axon connects the soma to a large number of extensions at the other end of the cell, longer axons are covered with fatty cells called Schwann cells, which together form the myelin sheath. Axons with a myelin sheath send nerve message faster, as the action potential can jump from space to space between the Schwann cells (the spaces are known as nodes of Ranvier), increasing the speed. On the end of each extension is an endplate; this is where the neuron connects to the dendrites of other neurons to pass on its message. In between the endplate of one neuron and the dendrite of another is a small empty (mostly) area known as the synapse. This article is about the Vedic plant and ritual. ... HeLa cells stained for DNA with the Blue Hoechst dye. ... In biology, a dendrite is a slender, typically branched projection of a nerve cell, or neuron, which conducts the electrical stimulation received from other cells to the body or soma of the cell from which it projects. ... An axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ... Schwann cells are a variety of neuroglia that wrap around axons in the peripheral nervous system, forming the myelin sheath. ... In neuroscience, myelin is an electrically insulating fatty layer that surrounds the axons of many neurons, especially those in the peripheral nervous system. ... This article is about anatomy; for the musical group see Nodes of Ranvier (band) Nodes of Ranvier are regularly spaced gaps in the myelin sheath around an axon or nerve fiber. ... Illustration of the major elements in a prototypical synapse. ...


Action Potential

Sensory receptors like those on the tongue change chemical signals into a moving electrical “potential”, which then travels through the nervous system (through many neurons) to the brain. When a stimulus is detected, the response is triggered and the “resting” potential changes to the action potential. While in resting potential, pumps in the neuron walls are constantly actively transporting 3Na+ ions out of the cell for every 2K+ ions that are pumped into the cell; this is accomplished by a structure known as a sodium-potassium pump. At the same time, an open ion gate is allowing K+ ions to flow down the concentration gradient back out of the neuron, while the ion gate for Na+ ions is closed. Thus, more positive ions are leaving the cell than entering, and the inside of the cell has a negative charge (-70mV). When an action potential is triggered, Na+ ions start to enter the cell through a separate gate, increasing the charge in the cell. This in turn triggers the voltage regulated Na+ and K+ channels in the cell wall to change shape. This opens the Na+ channel and closes the K+ channel. Sodium ions rush down the concentration gradient into the cell, but potassium ions are unable to escape, thus the potential in the cell rises to 40 mV. This potential in the cell causes other voltage regulated gates further down the cell to open, and the potential travels as a wave through the neuron, and into the next in the chain. After the potential has passed, the cell enters into a refractory period, to revert the potential to resting potential. To travel from one neuron to the next, the action potential must pass through the synapse. As the action potential travels down the axon, it triggers voltage regulated gates which allow Ca2+ ions to flow into the neuron. From this point there are several different routes which can be taken. Sometimes, these ions cause two or more free-floating chemicals within the cell to bond and form a secondary messenger known as a neurotransmitter. This neurotransmitter is then released from the cell into the synapse through exocytosis, when the vesicle (a small bubble containing the neurotransmitter) they are in merges with the pre-synaptic membrane. The neurotransmitter then goes on to trigger the opening of Na+ ion channels in the post-synaptic membrane, which allows Na+ ions to flow into the dendrite of the next neuron, continuing the action potential. Once the potential has been “passed on”, a different chemical causes the re-uptake of the neurotransmitter, breaking it down and returning it to the pre-synaptic neuron. Some neurotransmitters are acetylcholine, dopamine, serotonin, and GABA. The vesicle system of neurotransmitter release through exocytosis and return to pick up more neurotransmitter is known as the vesicle cycle and it involves, specifically, targeting, tethering, docking, release, membrane recovery and transmitter breakdown and vesicle recycling. The Human Nervous System The nervous system of a human coordinates the activity of the muscles, monitors the organs, constructs and also stops input from the senses, and initiates actions. ... A. A schematic view of an idealized action potential illustrates its various phases as the action potential passes a point on a cell membrane. ... Simplified Diagram of the sodium pump Na+/K+-ATPase (also known as the Na+/K+ pump or Na+/K+ exchanger) is an enzyme (EC 3. ... Chemical structure of D-Aspartic Acid, a common Amino Acid neurotransmitter. ... In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ... The chemical compound acetylcholine, often abbreviated as ACh, was the first neurotransmitter to be identified. ... Dopamine is a phenethylamine naturally produced by the human body. ... Serotonin (5-hydroxytryptamine, or 5-HT) is a monoamine neurotransmitter synthesized in serotonergic neurons in the central nervous system (CNS) and enterochromaffin cells in the gastrointestinal tract of animals including humans. ... Gaba may refer to: Gabâ or gabaa (Philippines), the concept of negative karma of the Cebuano people GABA, the gamma-amino-butyric acid neurotransmitter GABA receptor, in biology, receptors with GABA as their endogenous ligand Gaba 1 to 1, an English conversational school in Japan Marianne Gaba, a US model...


Taste as a form of Chemoreception

Taste is a form of chemoreception which occurs in specialized receptors in the mouth. These receptors are known as taste cells, and they are contained in bundles called taste buds, which are contained in raised areas known as papillae that are found across the tongue. To date, there are five different types of taste receptors known: salt, sweet, sour, bitter, and umami. Each receptor has a different manner of sensory transduction: that is, detecting the presence of a certain compound and starting an action potential which ultimately alerts the brain. It is a matter of debate whether each taste cell is tuned to one specific tastant or to several; Smith and Margolskee claim that “gustatory neurons typically respond to more than one kind of stimulus, [a]lthough each neuron responds most strongly to one tastant” (35). Researchers believe that the brain interprets complex tastes by examining patterns from a large set of neuron responses. This enables the body to make “keep or spit out” decisions when there is more that one tastant present. “No single neuron type alone is capable of discriminating among stimuli or different qualities, because a given cell can respond the same way to disparate stimuli” (39). As well, serotonin is thought to act as an intermediary hormone which communicates with taste cells within a taste bud, mediating the signals being sent to the brain. With that in mind, specific types of taste receptors will now be discussed. Receptor molecules are found on the apical (on top) microvilli of the taste cells. Taste buds (or lingual papillae) are small structures on the upper surface of the tongue that provide information about the taste of food being eaten. ... This page is a candidate to be moved to Wiktionary. ... This article includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ... In physiology, transduction is the conversion of a stimulus from one form to another. ... Serotonin (5-hydroxytryptamine, or 5-HT) is a monoamine neurotransmitter synthesized in serotonergic neurons in the central nervous system (CNS) and enterochromaffin cells in the gastrointestinal tract of animals including humans. ... Categories: Stub ...


Salt

Arguably the simplest receptor found in the mouth is the salt (NaCl) receptor. An ion channel in the taste cell wall allows Na+ ions to enter the cell. This on its own depolarizes the cell, and opens voltage-regulated Ca2+ gates, flooding the cell with ions and leading to neurotransmitter release. This sodium channel is known as EnAC and is composed of three subunits. EnAC can be blocked by the drug amiloride in many mammals, especially rats. The sensitivity of the salt taste to amiloride in humans, however, is much less pronounced, leading to conjecture that there may be additional receptor proteins besides EnAC that may not have been discovered yet. Ion channels are pore-forming proteins that help to establish and control the small voltage gradient that exists across the plasma membrane of all living cells (see cell potential) by allowing the flow of ions down their electrochemical gradient. ... Chemical structure of D-Aspartic Acid, a common Amino Acid neurotransmitter. ... Amiloride is an antihypertensive, a potassium-sparing diuretic that was first approved for use in 1967 and helps to treat hypertension and congestive heart failure. ...


Sour

Sour taste signals the presence of acidic compounds (H+ ions in solution). There are three different receptor proteins at work in sour taste. The first is a simple ion channel which allows hydrogen ions to flow directly into the cell. The protein for this is EnAC, the same protein involved in the distinction of salt taste (this implies a relationship between salt and sour receptors and could explain why salty taste is reduced when a sour taste is present). There are also H+ gated channels present. The first is a K+ channel, which ordinarily allows K+ ions to escape from the cell. H+ ions block these, trapping the potassium ions inside the cell (this receptor is classified as MDEG1 of the EnAC/Deg Family). A third protein opens to Na+ ions when a hydrogen ion attaches to it, allowing the sodium ions to flow down the concentration gradient into the cell. The influx of ions leads to the opening of a voltage regulated Ca2+ gate. These receptors work together and lead to depolarization of the cell and neurotransmitter release. Acidity redirects here. ...


Bitter

There are many different classes of bitter compounds which can be chemically very different. It is interesting that the human body has evolved a very sophisticated sense for bitter substances: we can distinguish between the many radically different compounds which produce a generally “bitter” response. This may be because the sense of bitter taste is so important to survival, as ingesting a bitter compound may lead to injury or death. Bitter compounds act through structures in the taste cell walls called G-protein coupled receptors (GPCR’s). Recently, a new group of GPCR’s was discovered, known as the T2R’s, which it is thought respond to only bitter stimuli. When the bitter compound activates the GPCR, it in turn releases gustducin, the G-protein it was coupled to. Gustducin is made of three subunits. When it is activated by the GPCR, its subunits break apart and activate phosphodiesterase, a nearby enzyme, which in turn converts a precursor within the cell into a secondary messenger, which closes potassium ion channels. As well, this secondary messenger can stimulate the endoplasmic reticulum to release Ca2+, which contributes to depolarization. This leads to a build-up of potassium ions in the cell, depolarization, and neurotransmitter release. It is also possible for some bitter tastants to interact directly with the G-protein, because of a structural similarity to the relevant GPCR. Wikipedia does not yet have an article with this exact name. ... The endoplasmic reticulum or ER is an organelle found in all eukaryotic cells that is an interconnected network of tubules, vesicles and cisternae that is responsible for several specialized functions: Protein translation, folding, and transport of proteins to be used in the cell membrane (e. ...


Sweet

Like bitter tastes, sweet taste transduction involves GPCR’s. The specific mechanism depends on the specific molecule. “Natural” sweeteners such as saccharides activate the GPCR, which releases gustducin. The gustducin then activates the molecule adenylate cyclase, which is already inside the cell. This molecule increases concentration of the molecule cAMP, or adenosine 3', 5'-cyclic monophosphate. This protein will either directly or indirectly close potassium ion channels, leading to depolarization and neurotransmitter release. Synthetic sweeteners such as saccharin activate different GPCR’s, initiating a similar process of protein transitions, starting with the protein Kinase A(PKA), which ultimately leads to the blocking of potassium ion channels.


Umami (Savory)

It is thought that umami receptors act much the same way as bitter and sweet receptors (they involve GPCR’s), but not much is known about their specific function. It is thought that the amino acid L-glutamate bonds to a type of GPCR known as a metabotropic glutamate receptor (mGluR4). This causes the G-protein complex to activate a secondary receptor, which ultimately leads to neurotransmitter release. The intermediate steps are not known.


Transmission to Brain

In humans, the sense of taste is conveyed via three of the twelve cranial nerves. The facial nerve (VII) carries taste sensations from the anterior two thirds of the tongue, the glossopharyngeal nerve (IX) carries taste sensations from the posterior one third of the tongue while a branch of the vagus nerve (X) carries some taste sensations from the back of the oral cavity. The facial nerve is seventh of twelve paired cranial nerves. ... This article includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ... The glossopharyngeal nerve is the ninth of twelve cranial nerves. ... The vagus nerve (also called pneumogastric nerve or cranial nerve X) is the tenth of twelve paired cranial nerves, and is the only nerve that starts in the brainstem (within the medulla oblongata) and extends, through the jugular foramen, down below the head, to the abdomen. ...


References

Bradbury, 2004. Taste Perception: Cracking the Code. <http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0020064> Article read on April 21, 2006.


Smith, David; Margolskee, Robert. 2001. Making Sense of Taste. Scientific American pp. 32-39; March 2001.


Gleason, Michael. 2004. Chemoreception. <http://www.biologyreference.com/Ce-Co/Chemoreception.html> Article read on April 21, 2006.


Watson, Flora. 2004. Tarsal Taste Receptors of Flies. <http://science.csustan.edu/flora/zool4232/Labs-S2005/fly-receptors.htm> Article read on April 21, 2006.


Scholey, J.M., et al. 2004. Biochemical Society Transactions. Biochemical Society. pp. 682-684.


Ward, Samuel. 1973. Chemotaxis by the Nematode Caenorhabditis elegans: Identification of Attractants and Analysis of the Response by Use of Mutants. PNAS Vol. 70, No. 3, pp. 817-821; March 1973.


Jacob, Tim. 2003. The Physiology of Taste. <http://www.cardiff.ac.uk/biosi/staff/jacob/teaching/sensory/taste.html> Article read on April 21, 2006.


Lindemann, Bernd. 2001. Nature Vol. 413, pp. 219-225; September, 2001.


Di Giuseppe, Maurice et al. 2003. Biology 12. Nelson. Toronto. pp. 438.


Boeree, George. 2003. General Psychology: The Neuron. <http://www.ship.edu/~cgboeree/theneuron.html> Article read on April 22, 2006.


Anonymous1. What is an action potential? <http://www.bio.brandeis.edu/biomath/mike/AP.html> Article read on April 22, 2006.


Koehler, Kenneth. 1996. The Action Potential. <http://www.rwc.uc.edu/koehler/biophys/4d.html> Article read April 22, 2006.


Anonymous2. 2006. Unit 10 - Neuronal Synapse. <http://mcdb.colorado.edu/courses/3280/lectures/class10.html> Article read April 22, 2006.


Bowen, R. 2003. Physiology of Taste. <http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/taste.html> Article read on April 22, 2006.


Purves, Dale et al. 2001. Neuroscience. Second Edition. Sinauer Associates Inc. Sunderland, MA.


Sugimoto, K. et al. 2002. Pure and Applied Chemistry. Vol. 74. No. 7. IUPAC. pp. 1148.


Becker, Lisa. 2007. The Neuron Psychology. <http://www.shenshina.com> Article read on Febrary 23, 2007.


Kalumuck, Karen. 2006. The Myth of the Tongue Map. <http://www.exploratorium.edu/ti/conf/nsta_2006/karen_kalumuck_session/Tonge%20Map%20Myths.pdf> Article read on April 23, 2006.


Bartoshuk, Linda. 1994. A Taste Illusion: Taste Sensation Localized by Touch. <http://www.bijouterieleroy.com/riedel3.htm> Article read on April 23, 2006.


  Results from FactBites:
 
Biology Department: Biology of the Gustatory System (1012 words)
Gustatory information from the tongue and oral cavity is processed in several CNS regions before reaching the gustatory cortex where perception occurs.
King, M.S. and Murphy, D.M., Morphology of projection neurons in the rat rostral nucleus of the solitary tract (rNST) and evidence for a projection to the rNST from the amygdala, Soc.
Recently, we have begun investigating the behavioral effects of microstimulation of discrete regions of the rat parabrachial nucleus (the second central structure in the ascending gustatory pathway).
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