The sense of taste is a chemical sense that can be used to determine the more precise nature of substances, especially food. In humans, the sensory cells of taste are located in the oral cavity, mainly on the tongue, but also in the oral and pharyngeal mucosa.
What is the sense of taste?
The sense of taste is a chemical sense that can be used to determine the more precise nature of substances, especially food. In humans, the sensory cells of taste are located in the oral cavity, especially on the tongue. Like the sense of smell, the sense of taste is a chemical sense that serves to absorb chemical stimuli from the environment. In contrast to the sense of smell, the sense of taste is a close sense, since it can only pick up stimuli from a substance when it comes into direct contact with it. The stimulus is perceived via specific chemical components of the substance, each of which stimulates precisely assigned taste cells. The taste stimulus is then transmitted to the brain via taste buds and evaluated there. This is closely linked to simultaneously perceived olfactory information. The final taste of a substance is therefore composed of chemical taste and odor information as well as the temperature and tactile perceptions from the oral cavity. At the current state of science, recognized basic tastes are sweet, sour, salty, bitter and umami (spicy). The taste of fatty is also currently being investigated and seems to be confirmed. Also being tested is the specific perception of the tastes metallic, aqueous, and alkaline.
Function and task
The receptor cells for taste in humans are located in the taste buds. Each bud contains between 50 and 150 taste receptor cells. Seventy-five percent of the taste buds are distributed on the tongue. The rest are found in the mucous membranes of the oral cavity and pharynx, on the upper esophagus, larynx and soft palate. Infants and young children not only have a greater amount of taste buds than adults. In addition, in them the buds are also distributed in the middle of the tongue, in the mucous membrane of the lips and cheeks, and on the hard palate. Then, as they age, the number and distribution of taste buds continues to decrease. On the tongue, the taste buds are arranged in differently shaped taste buds. About half of all taste buds in the mouth are located in the rear third of the dorsum of the tongue. Wallpapillae here contain several thousand taste buds in a V-shaped arrangement near the base of the tongue. Also in the posterior third of the tongue are the leaf papillae with several hundred taste buds at the edge of the tongue. Fungal papillae are found primarily on the anterior two-thirds of the tongue. There are up to 400 of them, each containing three to five taste buds. Each receptor cell can only perceive one particular flavor. However, receptor cells for different tastes are always arranged together in the taste buds. This ensures that each area of the taste buds can respond to all possible taste nuances. This extensive responsiveness is explained by the vital importance of the sense of taste: it allows humans to test ingested substances for their constituents before they are actually ingested. A sour or bitter taste can indicate unripe or fermented or even poisonous food. The tastes sweet, salty, umami and fatty often indicate the presence of nutritionally important components such as carbohydrates, minerals, proteins and fats. This facilitates the selection of needed foods and the avoidance of harmful foods. If taste cells are stimulated by the constituents of an ingested substance, this information is transmitted via the taste buds. These combine to form a total of three major cranial nerves: the facial nerve, the glossopharyngeal nerve and the vagus nerve. These are also referred to as VII, IX, and X, and they conduct taste perceptions to the brain.
Diseases and disorders
Diseases of the sense of taste are medically called dysgeusia. When the sense of taste is quantitatively impaired, a person may be hypersensitive (hypergeusia) or show decreased sensitivity (hypogeusia).A qualitative impairment manifests itself in taste sensations without a triggering stimulus (phantogeusia) or in altered taste sensations (parageusia). For example, if the taste sensations are altered in such a way that everything tastes unpleasant, the physician speaks of kakogeusia. Causes of disorders of the sense of taste can be divided into three areas:
First, dysgeusia can occur due to epithelial damage to the taste buds. For this, the taste buds can be damaged by flu-like infections or radiation therapy in the head area, among other things. The taste buds can also be damaged by diabetes mellitus, liver and kidney diseases, hypothyroidism or inflammation of the oral mucosa or tongue. Similarly, the intake of numerous active ingredients can affect the sense of taste. These include penicillamine, chlorhexidine, terbinafine and cytostatic drugs. Cushing’s and Sjögren’s syndromes are other possible causes of dysgeusia, as is poor oral hygiene. Damage to cranial nerves VII, IX, or X can also be a trigger for taste disturbance. The transmission of taste sensations through these nerves can be disturbed by tumors or inflammatory nerve diseases. Injury to the taste nerves is also possible due to a skull base fracture or during surgery on the teeth, ears, palatine tonsils or cervical lymph nodes. The third area that can affect the sense of taste involves central nervous causes. It concerns the so-called “tasting pathway”, i.e. the path that the transmission of the taste stimulus takes in the central nervous system. Disturbances here can be caused by injuries to the brain stem or brain tumors. Certain forms of epilepsy or neurodegenerative diseases such as Alzheimer’s can also affect the sense of taste. Likewise, some poisonings affect the sense of taste. An indirect impairment of the sense of taste also occurs through a disturbance of the sense of smell. Even a simple inflammation of the nasal mucosa (common cold) can therefore already cause a clearly perceived deterioration of the sense of taste. The reason for this is the combined processing of taste and odor information into a complex taste image in the brain.
