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== Taste perception: Current understanding ==
As per current biomedical understanding, there are five primary taste sensations viz., salty sour sweet bitter umami ()
=== Overview of the mechanism of taste perception<ref>Kimball JW. 15.9G: Taste. Published 2022. Accessed November 8, 2022. https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_Biology_(Kimball)/15%3A_The_Anatomy_and_Physiology_of_Animals/15.09%3A_Senses/15.9G%3A_Taste</ref> ===
<div style='text-align:justify;'>
Each taste bud comprises 50-100 taste cells that represent all five flavors. The apical surface of every taste cell is covered in receptors. These are transmembrane proteins that allow the chemicals that cause the flavors of sweet, bitter, and umami to bind to the ions that provide the taste of salt.
<br/>It appears that a single taste cell can only express one type of receptor (except for bitter receptors). Action potentials in a neighboring sensory neuron that connects to the brain are set off by a stimulated taste receptor cell. However, in each of the several taste buds, a single sensory neuron can connect to a number of taste cells. The brain is where all sensations, including taste, originate. </div>
{| class="wikitable" style="margin:auto; text-align:justify;"
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! Taste
! Plausible mechanism of taste detection
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| Salty
| The sodium ion channel that is activated by table salt (NaCl) in mice and possibly humans allows sodium ions (Na) to enter the cell directly, depolarizing it and causing action potentials in neighboring sensory neurons. The hormone aldosterone increases the number of these salt receptors in laboratory animals and maybe in humans. Biologically, this makes sense: Aldosterone's primary job is to keep the body's salt levels regular. An animal suffering from sodium deficiency (typically an issue for ungulates, including cattle and deer) would benefit from having a higher sensitivity to salt in its meal.
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| Sour
| Protons (H) released by sour substances are detected by sour receptors (acids). This causes transmembrane K channels to close, which causes the cell to become depolarized and release the neurotransmitter serotonin into the space where it connects to a sensory neuron.
|-
| Sweet
| G-protein-coupled receptors (GPCRs) are found on the cell surface and bind to sweet compounds (such sucrose, the table sugar). Each receptor consists of two T1R2 and T1R3 subunits that are connected to G proteins. Due of the G protein complex's structural and functional resemblance to the transducin, which is so crucial to rod vision, it has been given the name gustducin. A series of intracellular processes are triggered by gustducin activation, including the synthesis of the second messengers inositol trisphosphate (IP3) and diacylglycerol (DAG). This allows for the entry of Na ions, which depolarizes the cell and causes the release of ATP, which sets off action potentials in neighboring sensory neurons. It also releases intracellular Ca reserves. Leptin opens the K channels in sweet cells to suppress them. As a result, the cell becomes hyperpolarized, which makes it more challenging for action potentials to form.
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| Bitter
| Bitter compounds like quinine and phenylthiocarbamide [PTC] bind to gustducin-coupled G-protein-coupled receptors as well, and the signaling pathway is the same as for sweet drugs (and umami). Each taste cell sensitive to bitter expresses several (4–11) of the 25 distinct bitter receptors ("T2Rs") that are encoded by human genes. Despite this, and for reasons that are still unknown, a single taste cell appears to respond to certain bitter-tasting molecules in preference to others. (This is in stark contrast to the system in olfaction where a single odor-detecting cell expresses only a single type of odour receptor.) The brain is where all sensations, including taste, originate. Transgenic mice express a receptor for a tasteless substance in cells that normally express T2Rs (bitter), which are repulsed by the tasteless material, and T2Rs in cells that normally express T1Rs (sweet), which respond to bitter things as though they were sweet. Therefore, neither the chemicals nor the receptors themselves, but rather the activation of hard-wired neurons, determines the perception of taste.
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| Umami
| The reaction to glutamic acid salts, such as monosodium glutamate (MSG), a taste enhancer found in many processed foods and many Asian meals, is known as umami. Additionally, glutamate is present in processed cheeses and meats (proteins). On G-protein-coupled receptors that are connected to heterodimers of the protein components T1R1 and T1R3, amino acids, including glutamic acid, bind. The subsequent signalling chain is identical to that for sweet and bitter.
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== References ==
== References ==