Senses of Smell, Taste, and Touch: Mechanisms and Receptors

The Sense of Smell

The nose, equipped with olfactory nerves, is the principal organ of smell. The olfactory nerves are also important to differentiate the taste of substances found inside the mouth. Olfactory sensations are difficult to describe and classify. However, ratings have been looking at the chemical elements associated with the odor of substances. Research indicates the existence of seven primary odors: camphor, musk, flowers, mint, ether, pungent (vinegar), and rotten. These primary odors correspond to seven types of receptors on the cells of the olfactory mucosa. Research indicates that smell substances with similar odors are molecules of the same type. It is thought that these molecules are combined with specific cells of the nose, or chemical compounds that are within those cells. The capture of odors is the first step in a process that continues with the transmission of momentum through the olfactory nerve and ends with odor perception by the brain.

The Sense of Taste

Taste acts by contact of soluble substances with the tongue. Considered in isolation, the sense of taste can only perceive four basic tastes: sweet, salty, sour, and bitter. Each of them is detected by a special type of taste bud. Typically, the papillae sensitive to sweet and salty flavors are concentrated at the tip of the tongue, while the acid-sensitive and bitter-sensitive areas are at the sides and back, respectively. The food chemicals dissolve in the moisture of the mouth, and taste buds penetrate through the pores of the surface of the tongue, where they come into contact with sensory cells. When a receptor is stimulated by a dissolved substance, it sends nerve impulses to the brain.

The Sense of Touch

Through touch, the body perceives contact with various substances and objects. Humans have specialized nerve endings located in the skin, called touch receptors, which can be of three types: Meissner corpuscles, Merkel discs, and Pacinian corpuscles. These receptors are stimulated by a mechanical deformation of the skin and carry sensations to the brain via nerve fibers. The receptors are found in the epidermis and are distributed throughout the body variably, so some zones have varying degrees of sensitivity to touch based on the number of receptors they contain. Pacinian corpuscles are pressure-sensitive receptors, which are sensitive parts of the fingertips. Free nerve endings perceive both changes in pressure and temperature. Touch is the least specialized of the five senses, but with practice, acuity can be increased. For example, the blind have a delicate sense of touch that allows them to read the letters of the Braille system.

• Taste Buds:
  • Sweet
  • Salty
  • Sour
  • Bitter
• Touch Receptors:
  • Meissner corpuscles
  • Merkel discs
  • Pacinian corpuscles