Smell and Taste
The objectives of this section are to indicate.
• The sensations of taste and smell are age-dependent.
• Olfaction (smell) is experienced in the mouth, tongue and nose.
• Olfaction or the perception of smells is a very complex sensation which has not been totally defined chemically.
• Gustation (taste) distinguishes salt, sour, sweet, bitter and umami.
• Taste receptors recognise a wide range of chemical substances as having sweet and bitter properties.
Gustation is the term for the sense of taste and olfaction for the sense of smell. Together they make for the sensation of flavour. There are a large number of tastes and smells which add to the joy of eating and life in general. Good nutrition must include an enjoyment of food which is enhanced by good company and food with an appetising appearance and taste. Different animals have different sensitivities to smells for example dogs can be trained to detect explosives , drugs and people. Some smells smells are said to affect behaviour, certainly this is the case with insects with the smells of flowers but may apply to mammals. Such chemiclas are pheromes, which may haveamongst other properties have sexual attracting properties .
Taste qualities are divided into four or five sensations; salt, sour, sweet, bitter and umami. The latter is described as an amino acid type of taste, e.g. sodium glutamate. Each of these tastes is immediately recognised. Intensity only becomes relevant when a taste sensation is too strong or too weak.
Each of these tastes involves a single transducive nerve sequence and is associated with recognition of specific chemical structures. The appreciation of the flavour of food involves several sensory systems, mechanoreceptive, thermoreceptive and chemoreceptive. Many of the non-taste and non-olfactory sensations are carried to the brain by the trigeminal nerve (V). Taste is largely dependent upon multiple sensations, predominantly gustation and olfaction (smell). Taste is appreciated by specialised receptor cells in the mouth and palate which recognise chemical stimuli. The recognition of a chemical involves altering the firing rate of the sensory nerve. Gustation is the term the sensation of taste and olfaction for smell. In addition to the basic tastes of sweet, sour, bitter and salty there are a large number of tastes and smells.The recognition of the flavour of food involves several sensory systems, mechanoreceptive, thermoreceptive and chemoreceptive.
2. The olfactory system is capable of recognising thousands of smells. The system is very complex and it is not clear whether recognition takes place peripherally or centrally in the brain. The olfactory epithelium in humans is found predominantly on the dorsal aspect of the nasal cavity, the septum and part of the superior turbinates. The physical and chemical properties of olfactory mucus regulate the access of odorants to, and their clearance from, olfactory cells.
3. The olfactory bulb and receptors have an adult pattern by the middle of the 11th week of gestation. At about 28 weeks the olfactory system is capable of detecting chemical stimuli.
4. The chemoreceptor cells which experience taste sweet, sour, bitter and salty are arranged into buds in the oral cavity. Most taste buds are found on the upper surface of the tongue, though there are some in the soft palate, larynx, pharynx and epiglottis.
5. Taste cells are developed in the human foetus at 7–8 weeks’ gestation and morphologically mature cells are to be found at 14 weeks. The newborn baby enjoys sweet, sour and bitter tastes, and can discriminate tastes. The number of taste buds in the gustatory papillae does not decrease with age, and taste response remains in old age.
6. Saliva is produced by three large, paired salivary glands: the parotid, submaxillary and sublingual glands. It is a dilute aqueous solution that contains inorganic and organic constituents and has a cleansing, antimicrobial and buffering action that protects the teeth. The composition of saliva varies with time of day and degree and type of stimulation.
7. The sensation of sweetness is said to be appreciated by a sweet receptor called the AH,B system. There is a role in the sweet receptor site for the hydrophobic region of the molecule elsewhere in the sweet receptor.
8. The taste sensation is picked up by receptors and the information carried to the cerebral cortex by the VII and IX cranial nerve and processed into the sensation