Taste

Taste, along with the sense of smell and trigeminal nerve stimulation (registering texture, pain, and temperature), determines flavors of food and other substances.

[14] Among humans, taste perception begins to fade during ageing, tongue papillae are lost, and saliva production slowly decreases.

As of the early 20th century, Western physiologists and psychologists believed that there were four basic tastes: sweetness, sourness, saltiness, and bitterness.

[18] The detection of salt is important to many organisms, but especially mammals, as it serves a critical role in ion and water homeostasis in the body.

Many non-carbohydrate molecules trigger a sweet response, leading to the development of many artificial sweeteners, including saccharin, sucralose, and aspartame.

These are all critical molecules, and it is important to have a steady supply of amino acids; consequently, savory tastes trigger a pleasurable response, encouraging the intake of peptides and proteins.

Synthetic sweeteners such as saccharin activate different GPCRs and induce taste receptor cell depolarization by an alternate pathway.

[28] The most common foods with natural sourness are fruits, such as lemon, lime, grape, orange, tamarind, and bitter melon.

Common bitter foods and beverages include coffee, unsweetened cocoa, South American mate, coca tea, bitter gourd, uncured olives, citrus peel, some varieties of cheese, many plants in the family Brassicaceae, dandelion greens, horehound, wild chicory, and escarole.

The ability to detect bitter-tasting, toxic compounds at low thresholds is considered to provide an important protective function.

[18] The TAS2R family in humans is thought to comprise about 25 different taste receptors, some of which can recognize a wide variety of bitter-tasting compounds.

[17][49] MSG is a sodium salt that produces a strong savory taste, especially combined with foods rich in nucleotides such as meats, fish, nuts, and mushrooms.

[51][52] L-glutamate may bond to a type of GPCR known as a metabotropic glutamate receptor (mGluR4) which causes the G-protein complex to activate the sensation of umami.

Each type of receptor has a different manner of sensory transduction: that is, of detecting the presence of a certain compound and starting an action potential which alerts the brain.

Researchers believe that the brain interprets complex tastes by examining patterns from a large set of neuron responses.

Sweetness is detected by a variety of G protein-coupled receptors coupled to a G protein that acts as an intermediary in the communication between taste bud and brain, gustducin.

[66] Undissociated acid diffuses across the plasma membrane of a presynaptic cell, where it dissociates in accordance with Le Chatelier's principle.

Substances such as ethanol and capsaicin cause a burning sensation by inducing a trigeminal nerve reaction together with normal taste reception.

This "fresh" or "minty" sensation can be tasted in peppermint and spearmint and is triggered by substances such as menthol, anethol, ethanol, and camphor.

Caused by activation of the same mechanism that signals cold, TRPM8 ion channels on nerve cells, unlike the actual change in temperature described for sugar substitutes, this coolness is only a perceived phenomenon.

Both Chinese and Batak Toba cooking include the idea of 麻 (má or mati rasa), a tingling numbness caused by spices such as Sichuan pepper.

Some foods, such as unripe fruits, contain tannins or calcium oxalate that cause an astringent or puckering sensation of the mucous membrane of the mouth.

[citation needed] Other terms for the astringent sensation are "dry", "rough", "harsh" (especially for wine), "tart" (normally referring to sourness), "rubbery", "hard" or "styptic".

Volunteers were able to separate the taste of fatty acids into their own category, with some overlap with savory samples, which the researchers hypothesized was due to poor familiarity with both.

[97] There are few regularly consumed foods rich in fat taste, due to the negative flavor that is evoked in large quantities.

The lingual nerve (trigeminal, not shown in diagram) is deeply interconnected with the chorda tympani in that it provides all other sensory info from the anterior ⅔ of the tongue.

However, their taste spectrum extends to include water, fatty acids, metals, carbonation, RNA, ATP, and pheromones.

About 50% of patients with SARS-CoV-2 (causing COVID-19) experience some type of disorder associated with their sense of smell or taste, including ageusia and dysgeusia.

In fact there is a "plethora of methods"[128] Indeed, the taste index of 1, assigned to reference substances such as sucrose (for sweetness), hydrochloric acid (for sourness), quinine (for bitterness), and sodium chloride (for saltiness), is itself arbitrary for practical purposes.

The indices table for McLaughlin & Margolskee (1994) for example,[24][25] is essentially the same as that of Svrivastava & Rastogi (2003),[129] Guyton & Hall (2006),[60] and Joesten et al.

Taste bud
The diagram above depicts the signal transduction pathway of the sweet taste. Object A is a taste bud, object B is one taste cell of the taste bud, and object C is the neuron attached to the taste cell. I. Part I shows the reception of a molecule. 1. Sugar, the first messenger, binds to a protein receptor on the cell membrane. II. Part II shows the transduction of the relay molecules. 2. G Protein-coupled receptors, second messengers, are activated. 3. G Proteins activate adenylate cyclase, an enzyme, which increases the cAMP concentration. Depolarization occurs. 4. The energy, from step 3, is given to activate the K+, potassium, protein channels.III. Part III shows the response of the taste cell. 5. Ca+, calcium, protein channels is activated.6. The increased Ca+ concentration activates neurotransmitter vesicles. 7. The neuron connected to the taste bud is stimulated by the neurotransmitters.
The diagram depicts the signal transduction pathway of the sour or salty taste. Object A is a taste bud, object B is a taste receptor cell within object A, and object C is the neuron attached to object B. I. Part I is the reception of hydrogen ions or sodium ions. 1. If the taste is sour, H + ions, from acidic substances, pass through H + channels. Depolarization takes place II. Part II is the transduction pathway of the relay molecules. 2. Cation, such as K + , channels are opened. III. Part III is the response of the cell. 3. An influx of Ca + ions is activated. 4. The Ca + activates neurotransmitters. 5. A signal is sent to the neuron attached to the taste bud.
The diagram depicted above shows the signal transduction pathway of the bitter taste. Bitter taste has many different receptors and signal transduction pathways. Object A is a taste bud, object B is one taste cell, and object C is a neuron attached to object B. I. Part I is the reception of a molecule.1. A bitter substance such as quinine, is consumed and binds to G protein-coupled receptors.II. Part II is the transduction pathway 2. Gustducin, a G protein second messenger, is activated. 3. Phosphodiesterase, an enzyme, is then activated. 4. Cyclic nucleotide, cNMP, is used, lowering the concentration 5. Channels such as the K+, potassium, channels, close. III. Part III is the response of the taste cell. 6. This leads to increased levels of Ca+. 7. The neurotransmitters are activated. 8. The signal is sent to the neuron.
Taste buds and papillae of the human tongue
Taste receptors of the human tongue
Signal transduction of taste receptors
Active brain areas in taste perception
This diagram linearly (unless otherwise mentioned) tracks the projections of all known structures that allow for taste to their relevant endpoints in the human brain.