Physiology of Taste and Smell, Differences between Taste and Smell and How Flavour Relates to Them - Essay Example

Running header: Biology Student’s name: Instructor’s name: Subject code: Date of submission: Differences between taste and smell and how flavour relates to them Taste and smell are so much tangled in people’s experiences that many do not realize that most of what they think is taste is olfactory in nature. These sensations which are triggered by substances put into our mouths are composite involving more than just taste. For instance, an orange soda pop gives one a mixture of sweet and sour taste, it may be cold, sting or tingle a little like it is carbonated; it also smells fruity and fragrant. The only part of the sensation arising from taste-resulting from the tongue is the sweetness or sourness (Margaret, 1998). Furthermore, when one has a cold, he experiences flatness or blandness of his diet since the access of odorants to olfactory receptors is blocked by the mucus. This shows that taste and smell are much related and are determining factors in the kind of flavours we experience when we expose our mouths to different substances. Flavour may be defined as the sensation one realizes when he places a substance (e.g. food) in his/her mouth. The overall flavour results from a blend of responses to the receptors on the tongue, the mouth, throat and nose. The receptors trigger signals to the nervous systems which enable one differentiate various substances in sensory terms. This paper seeks to examine the difference between taste and smell and also explain how they relate to flavour. This will be done by explaining the various features of both the gustatory and the olfactory systems. Olfactory sensation-smell Overview This is a highly developed sense in most animals that is helpful in determination of flavours. Detection of smell is the function of chemo receptors found in the olfactory cells located in the olfactory epithelium on the nasal cavity (Fredric, 2008). This epithelium is covered by much hair like cilia whose function is to sense odorous molecules and stimulate olfactory sensations. For something to be smelled air has to be present and the substance has to be in gaseous state for its particles to enter nostrils in the course of sniffing. It must also be soluble in water so that the gaseous particles may dissolve in the mucus of the epithelium and initiate an impulse received by the brain. The olfactory cells react rapidly to stimuli and can detect odours at extremely low concentration. Anatomy Olfactory sensation or smell stems from the olfactory receptors found on the posterior segment of the nasal cavity in a mucosal area measuring around 5 sq cm. the olfactory epithelium is located on top of the cavity above the superior turbinate bones. The epithelium is yellow colored with no synchronously beating cilia hence differentiating it from the surrounding respiratory epithelia. The bowman’s glands that contain the yellow pigment and secret the mucus which covers the sensory epithelium are also found in the sensory region. The odorant has to dissolve in this mucus layer so as to reach the olfactory receptors. The receptor cells found on the olfactory epithelium are bipolar nerve cells unlike the receptor cells of the tongue that are specialized epithelial cells. The receptor cells have their nuclei in the lower side of the epithelium with their epical ends projecting to the surface. The ends are slightly enlarged with numerous cilia projecting out into the mucus. At their basal ends, the receptors are modified to an axon forming part of the olfactory nerve. The nerve fibers are not myelinated and are 0.2m in diameter. The nerve fibers converge onto mitral cells that send their axons to the piriform cortex, the olfactory tubercle and the periamygdaloid area. Unlike the gustatory pathway, the olfactory pathway does not relay in the thalamus although fibers leave the olfactory cortical region and relay in the thalamus into the hypothalamus where they regulate food intake and other behaviors dependent on olfactory information. Physiology of smell Microelectrode recordings from the epithelium give rise to two kinds of responses to olfactory stimulation. There is the slow wave potential evocative of the generator potentials of mechanoreceptors. The potential is however larger than the potentials recorded extracellulary from other single receptors. The potential does not have fixed bearing on the time of spike initiation. The potential is the summation of the nearby receptor cells and the potential from supporting cells. Secondly, there is the familiar spike discharges in the receptor cell axons. It should be noted that olfactory receptors are not specific but respond to a variety of odorants. The Gustatory sensation- taste Overview Taste results from the stimulation of the chemo receptors located on the taste buds on the tongue. The buds are tiny protruding that contains gustatory cells stimulated via taste pores which are tiny openings in the buds. The tongue’s rough surface is as a result of papillae that vary in shape and size. Examples of papillae are the circumvallate papillae that contain taste buds and form a V shape at the back of the tongue. Fungiform papillae which are mushroom shaped are found at the tip as well as sides of the tongue and also contain taste buds. Foliate papillae present on the folds along the sides of the tongue on the other hand contain lesser numbers of taste buds. Research has established that individuals with more taste buds have higher taste sensitivity. Apart from the taste buds, saliva is another significant component of the taste function since it acts as a solvent in which substances dissolve so that we can taste. Chewing on the other hand acts to stimulate secretion of the saliva together with other stimulus such as thought, sight as well as smell (Margaret, 1998). The combination of the factors usually lead to anticipation of the taste to be experienced even before the food is brought to the mouth. There are four generally accepted primary tastes that stimulate the taste buds at specific points of the tongue and hence taste buds are specific unlike the olfactory receptors. The four tastes include sweet, sour, bitter and salty. The sweet taste has been found to be predominantly recognized at the tongue’s tip and front, sour and salty tastes at the sides while bitter taste is recognized at the back of the tongue. Research has established that people usually confuse bitter and sour taste mainly because the two tastes often occur together in such products as lemons hence resulting into confusion about specifity. Anatomy of taste As earlier stated, the gustatory receptor cells are responsible for taste detection. These are found on taste buds of foliate, circumvallate and fungiform papillae found on the tongue. The taste buds are located in the taste pores and are composed of elongated sensory cells arranged along other non sensory cells just like in oranges segments. At the apical portions of the cells are microvilli projecting into taste pores which function by increasing surface area of the cell membrane. The cells respond to chemicals hence detecting the taste. Beneath taste buds, there are plexus of myelinated nerve fibers that carry impulses from the tongue to the nervous system’s chorda tympani of the seventh cranial nerve, lingual branch of ninth cranial nerve and pharyngeal of tenth cranial nerve which contain taste signals (Bruce 2001). The taste nerves on the other hand relay in the nucleus tractus solitarius and contract secondary cells organized in a topographical manner. These secondary cells in the brain stem project fibers to the ventral thalamus’ medial part adjacent to the somatic face projection from trigeminal nerve as well as to pontine taste areas. Physiology of taste The gustatory system detects and responds to various kinds of chemicals such that chorda tympani taste fibers respond to substances which are bitter, sour, sweet and salty. In other words, they respond to stimuli of two or more taste sub modalities. The nerve sends a brisk discharge ones sodium chloride or saccharin is put on the tongue although the nerve is only slightly excited by HCL, sucrose and quinine (Margaret, 1998). This implies that the quality of taste is only determined by the nervous system depending on the pattern of discharge across sensory nerve fibers. On the other hand, the intensity of taste depends on the number of impulses being discharged every second on the primary taste fibers. This way, the taste function in conjunction with the smell and texture functions play an important role in the sensation of flavours by animals as well as human beings. Smell and taste relationship to flavours As earlier stated, the senses of smell and taste play a crucial role in an individual’s perception of flavours. It is the combination of both the sense of smell and the sense of taste in conjunction with the tactile sensation of the touch sense that provide the flavour of various products. Once we place food in our mouths, we will recognize the primary taste of the food or drink on our tongues in conjunction with texture sensation as well as other related sensations found in the mouth’s palate. The taste will be identified owing to the volatile components that move from the back of the mouth to olfactory area where the sense of smell is in action (Margaret, 1998). Actually, when one says that he/she has lost the sense of taste, it is the sense of smell that is usually not being detected. This is the reason why people with common cold have problems with identifying tastes and hence flavours which is related to the volatile components and hence the olfactory function. This is owing to the fact that during colds, the olfactory epithelium earlier discussed becomes unable to send impulses to the brain as mucus on the surface impede the volatile components and hence the detection mechanism fails. The result of this is imbalance making one to have an impression of flavour that is distorted since the volatile components which confer identity can not be recognized. Flavour and appeal to food relates to the senses of taste and smell and are essential criteria through which one judges food before deciding on whether to consume. A good flavour may entice one into consuming the food while a bad flavour may deter one from consuming the food (Catherine and Benoist, 2002). In essence, flavour is a combination of both taste and smell. Other senses that determine the appeal for food include the sight and texture. The olfactory and gustatory sensations play a great role in determining the flavour of food and hence are indicative of the expected characteristics of the food product which include how fresh it is, its appropriateness and the quality of flavour. The qualities of taste and smell also determine the kind of flavour experienced in a product. As such, they may give rise to positive or negative response on the product depending on what product it is. A desirable flavour in one product may not be desirable in another (Margaret, 1998). For instance, the intensity of bitterness varies in beer and coffee and is desirable but it may not be desirable in oranges. This shows how important the senses of smell and taste are in determining flavour of food products and may determine whether the food product is accepted or not. Conclusion This paper has established that both the taste and smell function play an important role in flavour sensation. it is the characteristics of the senses of smell and taste experienced in a product that determine what kind of flavour the product has or is expected to have. However, a number of differences have been established between the olfactory sensation and the gustatory sensation. It has been established that gustatory sensation is mediated by taste buds that are located on the tongue’s papillae while olfactory sensations are mediated by the olfactory receptors found on the posterior segment of the nasal cavity. Four taste sub modalities have been established which include sweet, sour, salty and bitter which are not entirely independent as they interact in successive tastings. Different taste stimuli yield different sensations at different levels of concentration. On the other hand, olfactory sensations are triggered by volatile substances though no primary sub modalities have been established although they respond to different odorants. References: Fredric, M2008, Fundamentals of anatomy and physiology, Benjamin Cummings, London. Bruce E, 2001, Sensation and perception, Woods worth publishing company, Sydney Catherine, R and Benoist, S, 2002, olfaction, taste and cognition, Cambridge university press, Cambridge. Margaret, P, 1998, Symposium on ‘taste, flavour and palatability’: Taste and flavour perception, Nutrition society, 57,603-607. Read More