[Assessment of the correlation between taste and smell functioning].
Taste and Olfaction. This page contains a few, relatively straightforward points about taste and olfaction. Taste. As shown to the right, each taste bud consists of a. In fact, he said studies have shown a big connection between lowered sense of smell and the likelihood that a person will develop such. The Science of Mouth and Nose – How We Taste and Smell . The Science of Taste and Smell · The Relationship Between Taste and Smell · Smell and Taste.
The axons from all the olfactory neurons of one type converge on one cluster in the olfactory bulb. There they form synapses with neurons with axons in the olfactory tract.
The olfactory bulb actually is a lobe of the brain. You might not guess this in a human brain, but in lower vertebrates it is obvious, with the olfactory bulbs often being larger than the cerebral hemispheres. Taste information enters the brainstem and evokes rather simple behaviors, such as secreting saliva, or perhaps spitting something bitter out.
Smell information, by contrast, projects into the medial temporal lobe near the midline of the cerebrum. This places it close to areas important in emotions and motivations.
Taste and Olfaction
And corresponding to this, smells often call up complex, emotionally rich thoughts. When stimulated, these cells send signals to specific areas of the brain, which make us conscious of the perception of taste. Similarly, specialized cells in the nose pick up odorants, airborne odor molecules. Odorants stimulate receptor proteins found on hairlike cilia at the tips of the sensory cells, a process that initiates a neural response.
Ultimately, messages about taste and smell converge, allowing us to detect the flavors of food. Just as sound is the perception of changes in air pressure and sight the perception of lighttastes and smells are the perception of chemicals in the air or in our food. Separate senses with their own receptor organs, taste and smell are nonetheless intimately entwined.
Taste and Smell
This close relationship is most apparent in how we perceive the flavors of food. Actually, what is really being affected is the flavor of the food, or the combination of taste and smell. Use of this term avoids the confusion otherwise produced by using taste to refer specifically to the sensations produced by stimulation of taste receptors, as well as to the combined sensations of taste and smell.
Although the same arguments apply to other terrestrial vertebrates, there is little knowledge of the extent to which flavour, as opposed to taste, is important in other organisms.
This entails processes that are initiated at the taste or smell receptor cells. First, the molecule must be captured in and traverse a layer of mucus, in which the endings of the receptor cell are bathed; these are known as perireceptor events. Second, the molecule must interact with the surface of the receptor cell in a specific way to produce reactions within the cell.
These reactions lead to a change in cellular electrical charge, which generates a nerve impulse.
Taste and Smell
Transformation of an external stimulus into a cellular response is known as signal transduction. The electrical signal produced by a particular nerve cell is the same regardless of the nature of the stimulus.
If chemicals are to be distinguished from one another, they must stimulate separate cells. Thus, different cells are responsible for the reception of sweet, salt, sour, and bitter tastes and for distinguishing the different odours detected by the olfactory system.
Perireceptor events Water-soluble compoundssuch as sugars and amino acidscan move freely in the mucus covering the taste and olfactory receptor cells. However, most bitter-tasting and many volatile compounds are not water soluble and must be made soluble if they are to reach the receptors. This is achieved by binding them to soluble proteinswhich can move freely through the mucus. Such proteins have been isolated both from saliva and from the mucus in the nasal epitheliumalthough the precise role of soluble proteins in transporting chemicals to receptor cells has yet to be clearly demonstrated in mammals.
In insectstaste and olfactory neurons are contained within cuticular structures, but the sensitive nerve endings are bathed in a fluid called sensillar lymph that is analogous to the mucus of vertebrates. In the olfactory system this fluid contacts odour-binding receptors that presumably function in the same way as those of vertebrates but that are produced by different families of genes.
Three families of these receptor proteins have been identified.
- [Assessment of the correlation between taste and smell functioning].
One family, consisting of pheromone -binding proteins, is restricted to receptors known to be sensitive to pheromones. The remaining two families contain general odorant receptors that respond to other odours not pheromones. These proteins, to differing extents, govern which chemicals reach the membrane of the receptor cell and can be regarded as filters.
Differences in their binding capacity could account for some of the differences in sensitivity of different receptor cells. It is important that taste and odour molecules be removed from the immediate environment of the receptor cell; otherwise the cell, and thus the animal, continues to respond to something that is no longer relevant.
Removal of the unwanted molecules is thought to be achieved, at least in part, by odorant-degrading enzymes that are also present in the mucus or other fluid surrounding the sensitive endings of the receptor cells. Signal transduction Information is conveyed along neurons by electrical signals called action potentials that are initiated by electrical changes in receptor cells. In the case of chemoreceptorsthese electrical changes are induced by chemicals.
The initial changes are called receptor potentialsand they are produced by the movement of positively charged ions e. Thus, in order to stimulate a receptor cell, a chemical must cause particular ion channels to be opened. This is achieved in various ways, but it most commonly involves specific proteins called receptors that are embedded in the cell membrane. Within the cell membrane, receptor proteins are oriented in such a way that one end projects outside the cell and the other end projects inside the cell.
This makes it possible for a chemical outside the cell, such as a molecule of an odorant or a tastant compoundto communicate with and produce changes in the cellular machinery without entering the cell. The outer and inner ends of receptor proteins involved in taste and smell are connected by a chain of amino acids. Because the chain loops seven times through the thickness of the cell membrane, it is said to have seven transmembrane domains.