What Are Taste Buds?
Introduction
Have you ever wondered why a particular type of food tastes so good? Your taste buds let you recognize different food flavors such as the saltiness of chips and the sweetness of candies or doughnuts.
According to ancient Greek view, that there are seven basic tastes, which consist of sour, bitter, salty, sweet, pungent or spicy, astringent (dryness), and harsh. Out of all the tastes, there are five that the tongue is sensitive towards and they are, sweet, sour, salty, bitter, and umami, which corresponds to the flavor of monosodium glutamate. Umami is a Japanese term used when referring to a "savory" or "meaty" taste.
1. Salty
The taste of saltiness is known to be produced by the very presence of sodium chloride and other types of salts to a lesser degree. The ions present in the salt, especially sodium, tend to directly pass through these ion channels into the tongue leading to a potential action.
2. Sour
Most acidic solutions such as organic acids and lemon juice are sour in taste. The actual mechanism to detect a sour taste is quite the same to detecting saltiness. The concentration of hydronium ions, which are formed from water and acids are detected by hydrogen ion channels. Hydrogen ions can permeate amiloride-sensitive sodium channels. However, it is not the only mechanism involved when it comes to sourness detection.
3. Bitter
Bitter is known to be the taste that detects bases. Similar to sweetness, bitterness is sensed by the G protein, which is coupled up with receptors and the G protein gustducin.
Most of the time, certain individuals find that the bitter taste is quite unpleasant. Many alkaloids tend to taste bitter. Sensory cells have around 35 proteins that respond to substances that are bitter. There are various bitter species of plants and some of them are poisonous. From an evolutionary viewpoint, it was a matter of survival for man to learn how to recognize which ones were poisonous to avoid accidental poisoning.
4. Umami or Savory
Umami is a savory taste sensation, which is said to be caused by aspartic acid or glutamic acid. These glutamates are commonly found in certain aged or fermented food items. In English terms, it is described as "meaty" or "savory". In Japanese, the term umami would mean that it has "a delicious flavor to it".
A savory taste is considered as one of the fundamental tastes in Japanese as well as Chinese cooking, but not much discussed in the Western cuisine.
5. Sweet
The taste of sweetness is usually caused by the presence of sugar, certain proteins, and sugar derivatives such as lactose and fructose.
Sweetness is often connected to ketones and aldehydes, which consist of the carbonyl group. The taste of sweetness is detected by a variety of G proteins, which are coupled up with receptors and the G protein gustducin found in the taste buds. There has to be an activation of at least two of the different variants of sweet taste receptors for the brain to register the taste of sweetness.
What are taste buds?
Taste buds are basically sensory organs found on the tongue. Taste buds allow people to experience different tastes, which can be sweet, sour, salty, bitter, or umami. But how do taste buds work? To find out, stick out your tongue and have a closer look at it in the mirror. Do you see all those small bumps present on your tongue? They are called as papillae, and most of them contain taste buds.
Taste buds contain very sensitive microscopic hairs called as microvilli. These tiny hairs send messages to the brain about how a certain food item would taste, which is how we get to know whether the food or liquid we consume is sweet, sour, bitter, spicy, or umami.
An average person has around 10,000 taste buds, which are replaced every two weeks. However, as people age, many taste buds do not get replaced. In the case of an elderly individual, there are around 5,000 working taste buds. In such cases, certain food items would not taste stronger than it would taste for an adult. Smoking can also reduce the number of taste buds an individual has.
Taste buds contain taste receptors, which are also medically called as gustatory cells. They are usually located just around the papillae present on the upper surface of the tongue, upper esophagus, epiglottis, soft palate, and cheek. These structures are known to be involved in the detection of the five main elements of taste, which are salty, sour, umami (savory), sweet, and bitter.
We tend to detect correct flavors even if we taste various flavor combinations. The tongue map has been around for ages, wherein it maps the basic tastes on the tongue. However, this notion is wrong because the entire tongue is capable of sensing all of the basic tastes, which means that a particular taste can be detected by any area of the tongue no matter which region it belongs to.
With the presence of small openings in the tongue epithelium known as taste pores, there are certain portions of food that are dissolved in the saliva, which come into contact with taste receptors and are placed on top of the taste receptor cells, which constitute the taste buds. The taste receptor cells then send out information, which gets detected by clusters of various receptors and ion channels to the gustatory regions of the brain through the seventh, ninth, and tenth cranial nerves.
However, before you give credit to your taste buds for taste sensations, you should also thank your nose. A food’s flavor is produced when its taste is combined with its smell. If an individual has an impaired sense of smell due to a cold, stuffy nose, or allergy, then the taste perception is also affected.
Types of Papillae
The papillae are wart-like projections seen under the tongue’s mucous membrane. They usually function by intensifying individual tastes. They contain numerous taste buds, which have around 10-15 sensory cells. They are also categorized according to their shape:
- Fungiform Papillae: They are slightly in the shape of a mushroom if viewed in the longitudinal section. They are also mostly present at the tip of the tongue.
- Foliate Papillae: They are ridges and grooves toward the posterior portion of the tongue and are found at the lateral borders.
- Circumvallate Papillae: Every individual only has 7-12 of this type of papillae. However, the papillae contain thousands of taste buds. They are visible to the naked eye and forms a V-shape arrangement at the back of the tongue.
How Taste Buds Work
When we chew our food, there is a release of certain chemicals, which immediately travel up into our nose and trigger olfactory receptors. These olfactory receptors work along with the taste buds to create the food's true flavor by informing the brain about it.
It is the reason why we cannot sense much flavor in food when we have a stuffy nose due to allergies or colds. When we have these conditions, the upper portion of our nose has a difficulty in receiving the chemicals that trigger the olfactory receptors, which tell the brain as well as create flavor sensations.
On your next meal, try holding your nose when you eat something. You would notice that your taste buds are capable of telling your brain what kind of food you're eating. However, you cannot identify the food's true flavor until you let go of your nose.
Issues Concerning Taste
An impaired taste would mean that an individual's sense of taste is not functioning as it should be. Taste impairment also refers to the absence of taste or an altered sense of taste such as having a metallic taste in the mouth.
Most of the time, individuals may experience a temporary impaired taste and lose their ability to taste. It is quite rare for people to completely lose their sense of taste. The causes of an impaired taste may be due to a common cold or serious medical complications, which may involve the central nervous system.
An impaired taste is also a sign of the normal aging process. It has been estimated that around 70 percent of people who are above the age of 80 have an impaired taste.
Causes
There are a wide variety of causes for an impaired taste. Many of the causes are known to involve the respiratory system. The following conditions can have an effect on an individual's ability to taste:
- Flu
- Sinusitis infection
- Common colds
- Salivary gland infections
- Certain throat infections such as pharyngitis or strep throat
Apart from the ones mentioned above, the other reasons that may lead to an impaired taste would include:
- Inflammation of the gums leading to periodontal disease or gingivitis
- A deficiency of important nutrients such as zinc or vitamin B12
- Head or ear injuries
- Smoking
- The use of certain medications, which include lithium and medications for thyroid disorders as well as cancer
- Sjogren's syndrome, which is an autoimmune disorder that causes mouth and eye dryness
Any disorder of the nervous system is also known to cause an alteration in the sense of taste. Disorders of the nervous system are said to affect on how the nerves would send out the messages to the rest of the body.
The organs of the body that are known to control taste may also be affected due to nervous system impairment. Individuals diagnosed with Bell’s palsy or multiple sclerosis are also known to experience taste impairment.
