Common perception is that the small elevated buds in the tongue are taste buds. That’s not true. Small elevated buds are papillae and they belong to four different kinds – fungiform, filiform, and foliate and vallate. Fungiform and filiform care found in the tip of the tongue extending to the middle while foliate and vallate are seen from the middle to the back of the tongue. Taste buds that we talk about are located within these papillae grouped in numbers ranging from 2 to 250. Taste buds are described to be in the shape of onions or small navel oranges. Taste buds have about 200 cells that can be classified as a receptor or basal. Taste buds have 5 primary taste senses – salt, sweet, bitter, sour and umami.
Tastants produce tasting ability by response to dissolution of ions and molecules. Taste receptor cells help us in detecting taste. Taste receptor cells are grouped in taste buds. There is a pore in each taste bud to facilitate dissolved molecules in the mouth to be received by the receptors. When we eat tasty food and the food enters the mouth, it is dissolved by the saliva by breaking the chemicals into ions and molecules. These floating molecules enter the pores.
A taste bud has taste cells of all 5 tastes. Every taste cell has receptors on its surface. The receptors consist of transmembrane proteins that help them to attach to free molecules to produce the taste sensations. It is possible that only one taste sensory receptor is active in the cell when compared to other sensory receptors. Since bitter and sweet are extreme tastes, both these tastes are not found active in a single cell on normal conditions.
A synapse connects the receptor cell to the sensors related neurons to the brain. A sensor related neuron can connect many taste cells in different more taste buds. As in the case of all senses, taste sensation lies in the brain.
Sweet and bitter tastes activate gustuducin that results in a electrochemical transmission between receptors and basal cells and the information is relayed to the gustatory cortex in the brain which says ‘this is sweet’. In the case of salt and sour tastes, sodium and potassium ions increased positive charge buildup generated a small electric current that gets transformed to the brain as something salty or sour is being eaten.
A person has 10000 taste buds that get replaced about every 2 weeks and this process weakens with age and certain taste cells are not replaced. This is the reason for a child experience stronger taste than adults.
The role of olfactory senses is clearly stated in physiology of taste. Onion and Strawberry taste the same way if the eyes and nose are tightly closed. Flavor is more significant in adding taste to the food and our senses identify the food by smell much before it is tasted.