Integrative Oral Sciences 1507
Chemical Sensory System Functions

by Dr. M. Hutchins

OVERVIEW

The chemical senses, taste & smell, are important sensory systems that are essential for the selection of foods which are necessary for nutrition and metabolism. They are contact  senses, i.e. chemicals must be in solution and make contact with the taste receptors in the taste pore of the taste buds; while odorant molecules must be present in inspired air, contact theolfactory mucosa and then bind to the olfactory receptors.

Both of these chemical senses can adapt or alter their sensitivity to specific taste molecules or to odors. This process is not fully understood, but research indicates that repetitive exposure can inactivate or alter the respective membrane receptor. For example, our sensitivity to salt or sucrose can be enhanced if we reduce the concentration of salt or sugar added to our diet.

An odor, that seems initially seems very intense to humans is not identified after prolonged exposure. Dental patients may not recognize that their breath is malodorous, yet complain of the odor in a dental clinic.

Flavor of foods is the major reason that humans select certain foods for enjoyment. It is dependent primarily upon our ability to distinguish between the 4 categories of taste ( umami or the taste of monosodium glutamate is considered by some cultures to be the fifth quality) and  to discriminate between  the 6 classes of odors (Fig. 2). The flavor of foods is also dependent upon the flow and dissolution of foods with saliva; upon mastication which brings the dissolved food into contact with the oral mucosa & tongue. Thorough mastication of foods permits stimulation of the afferent fibers of the Trigeminal nerve to distinguish touch, temperature, and even pain to fully enjoy selected favorite foods, hot sauces and liquids.

An appreciation of and changes in the flavor of foods  also depends upon other foods that have been previously eaten and the amount of water present in the prepared food. Humans who wish to have a discriminating taste for different wines or foods(e.g...judge for a chili cookoff) should rinse with distilled water between samples to improve perception.   Neuroanatomically stimulation of the afferent cranial nerves; I, V, VII, IX, and X  occurs in order for the central nervous system to perceive and identify consumed liquids, and foods.

Figure 1
Role of mastication and saliva in appreciation of flavor
Figure 3

A study late in 1980 indicated that 2-3 million Americans suffer  from a deficiency in some type of chemosensory function . Many complain of a taste disorder, but this study determined that a majority of these individuals instead have a partial loss in the sense of smell.
Figure 4

Dental patients without a loss in taste or smell function and treated with a prosthesis that partially covers the palate may complain that the prosthesis has acutely altered the flavor of foods because the appliance has compromised sensory input from the oral cavity by the Trigeminal nerve. Some dental patients have a reduced salivary flow due to medicinal drug use and complain of a “bad taste” or “food does not taste good”.


 


Content questions should be directed to: Dr. Max Hutchins
Copyright © 2001, All Rights Reserved
The University of Texas Health Science Center at Houston (UT-Houston)
Created by the staff of the Multimedia Scriptorium