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Why do we study taste and smell together? SENSORY INTERACTION: the principle that one sense may influence another. The senses of taste and smell have a very cooperative working relationship. Many of the subtle distinctions you may think of as flavors really come from odors n Often, if you can’t smell the food, you can’t taste the food.
Five Distinct Tastes: n Each of these tastes developed as survival functions, according to evolutionary psychology. Sweet energy source Sour – potentially toxic acid Bitter – potential poisons Salty – sodium essential to physiological processes Umami – proteins to grow and repair tissue =the taste of glutamate (MSG) – savory taste in meat and cheese
A Theory Debunked Since 1942, tongue maps like this one were widely published and touted as an accurate portrayal of where certain taste receptors were located. n Wine glasses are even designed around this idea. The notion that the tongue is mapped into four areas—sweet, sour, salty and bitter—is wrong. There are five basic tastes identified so far, and the entire tongue can sense all of these tastes more or less equally. The tongue map is easy enough to prove wrong at home. n n Place salt on the tip of your tongue. You'll taste salt. For reasons unknown, scientists never bothered to dispute this inconvenient truth until 1974, and even today, many textbooks still publish pictures of the tongue map. Remarkably, more is known about vision and hearing, far more complicated senses, than taste.
Gustatory system Although we speak about taste it is always a combination of odors (~ 75%) and tastes (~25%) 4 types of papillae on the surface of the tongue: 1. pp. filliformes (vlaknate), they do not contain taste buds, so they are not a part of the gustatory system 2. pp. circumvallatae (opkopane), 10 12, “V” shape 3. pp. fungiformes (gljivaste, mushroom like), mostly on the top and on the lateral edges 4. pp. foliate (listaste), mostly in the posterior part
Papillae Those bumps on our tongue are called papillae. Papillae help grip food while your teeth are chewing. They also have another special job n Each has 200 or more taste buds Individuals vary in their sensitivity to taste sensations, a function of the density of these papillae on the tongue.
Taste Buds Each taste bud pore has 50 100 taste receptor cells with antenna like hairs that sense food molecules
(a) Taste buds line the trenches around tiny bumps on the tongue called papillae. There are three types of papillae, which are distributed on the tongue as shown in (b). The taste buds found in each type of papillae show slightly different sensitivities to the four basic tastes, as mapped out in the graph at the top. Thus, sensitivity to the primary tastes varies across the tongue, but these variations are small, and all four primary tastes can be detected wherever there are taste receptors. (Data adapted from Bartoshuck 1993 a).
Taste receptors reproduce themselves every week or two (this is why it hardly matters if you burn your tongue with hot food). As you grow older, the number of taste buds decreases, as does taste sensitivity.
Taste As with other senses, your experiences influence your brain’s response. n n n If you are told something is going to taste bad, your brain responds more negatively. Reversely, drinking coffee from your favourite cup will taste 10 20% better Likewise, being told that a wine costs $90 rather than its real $10 price makes an inexpensive wine taste better and triggers more activity in a brain area that responds to pleasant experiences. As happens with the pain placebo effect, the brain’s thinking frontal lobes offer information that other brain regions act upon.
Receptors for a given taste on apical surface of taste cells
Gustatory pathway starts with gustatory cell of the taste bud (not with a neuron) First synapse is the one between the basal surface of the sensory cell and primary afferent axon (bodies of the 1 st neuron are in sensory ganglia of the CN. VII, IX, X (g. geniculi ext. , g. petrosum, g. nodosum) N. VII inervates the first 2/3 of tongue surface, N. IX posterior 1/3, and N. X small number of taste buds on epiglottis Central processes of these neurons end on rostral, “gustatory” pole of the solitary nucleus (polus gustatorius n. solitarii) (2 nd neuron of the gustatory pathway) Collaterals of these axons end up on the salivatory nuclei (for secretion of saliva) and dorsal vagal nucleus (reflex secretion of gastric juices)
Gustatory pathway cont. Most of the axons of the 2 nd neuron of the gustatory pathway project to n. parabrachialis medialis in the lateral tegmentum, where is the soma of the 3 rd neurona Aksons of the 3 rd neurona ascend through medial part of the LM into ipsi and contralat. VPM thalamic nucleus (pars parvocellularis); smaller portion of axons of the 2 nd neuron come directly to VPM th. n. (so, in th. is 3. or 4. neuron of the path) Thalamocortical “gustatory” projection end up in. BA 43 (ventral surface of the juncure of pre and postcentral gyrus in the ‘roof’ of the lateral sulcus of Sylvius) (4. or 5. neuron of the gustatory path)
Osmoreceptors Most of the osmoreceptor neurons are located in OVLT (organum vasculosum laminae terminalis), where the capilaries of the BBB are fenestrated (hypovolemic thirst) These neurons project on vasopressin neurons in n. supraopticus and n. paraventricularis on the anterior hypothalamus (which themselves have osmoreceptors that react on osmotic stimuli and changes of Na concentration in blood)
Olfaction Our Sense of Smell What's in a name? That which we call a rose by any other name would smell as sweet. William Shakespeare
How Olfaction Works Smell (Olfaction): operates much like the sense of taste. n The physical stimuli are chemical substances carried in the air that are dissolved in fluid, the mucus in the nose. Pathway: Olfactory cilia -> neural impulse -> olfactory nerve -> olfactory bulb (brain) n n Olfactory receptors (olfactory cilia) and are located in the upper portion of the nasal passages. The olfactory receptors instantly alert brain through axon fibers the brain. Olfaction is the only sense that is not routed through the thalamus. This suggests that smell develops earlier than the other senses.
How Olfaction Works Receptor proteins are embedded on the surface of nasal cavity neurons n n As a key slips into a lock odor molecules slip into receptors Some odors trigger a combination of receptors Odors are not easily classified. n Humans can distinguish among about 10, 000 odors, but for some reason have a hard time attaching names to odors quite frequently.
Chemoreceptors of the olfactory system - Olfactory epithelium consists of 3 types of cells - Primary aferent (bipolar) neurons are constantly renewed from basal cells (every 30 days); their 10 -20 immovable ciliae contain olfactory receptor molecules - Whole olfactory pathway is fully ipsilateral
Bipolar cells (1. ) Olfactory pathway Mitral and tufted cells (2. ) in the olf. bulb 3. Their axons make olf. tract which divides into med. i lat. olf. stria making trigonum olf. in which we see tuberculum olf. Cortex praepiriformis (primary olf. cx), n. olf. ant. , cx periamygdaloideus, etc. Kandel, 2000
100 snopića njušnog živca Buck, Linda and Axel, Richard (1991) A novel multigene family may encode odorant receptors: a molecular basis for odor recognition. Cell, 65, 175 -187. 6 milijuna NPW 2004 >1000 gena za rec. mirisa (7 TM) = >3 % genoma
Mitral cells are principal neurons of the olf. bulb. Their primary apical dendrite extends into spherical glomerulus (about 25 mitral cells converge to one glomerulus), which accepts axons primary olfactory neurons. Axons of mitral cells make tzv. lateral olfactory tract. These axons give collaterals involved in pos. and neg. feedback control. The architecture of the bulb results in 1: 1000 convergence of olfactory receptor neurons to Centrifugal pathways have a "wipe clean" mitral cells. Thus a lot of function to reset the system ready for the information about individual receptors is thrown away but this next input and also with disinhibition. increases sensitivity since When hungry smells have a greater effect! contributions from many receptors are added together.
Olfactory pathways Most important projections of the praepiriform cx: Orbitofrontal cx (discrimination of odors) Mediodorsal th n. (pars magnocellularis), also projects to orbitofront. cx basal telencephalon, pro and entorhinalni cx, hipp. formation, lat. hipoth. (through n. accumbens septi): affective component of smell (“Prousts phenomenon”, + aura – olf. halucinations)
Olfactory system – interesting facts Most odor molecules have mol. mass less than 350 k. Da Night butterflies can smell single molecule of bombicol (pheromone) Polar bears can detect a seal or whale carcass from as far away as 32 60 km
Smell in space Research has shown that your olfactory sensitivity depends upon body position. Lie down, and you become less sensitive. [Lundstrom et al. , (2006) "Sit up and smell the roses better: olfactory sensitivity to phenyl ethyl alcohol is dependent on body position". Chemical Senses 2006. Although they give a number of reasons for this phenomenon, it may be as simple as the decreased effect of gravity on the blood pressure, as in astronauts. Astronauts tend to lose their senses of smell and taste. This is thought to be because to the congestion in the nose resulting from the increased capillary pressure as the heart no longer has to work against gravity. As a consequence the sinuses tends to fill up with fluid, giving rise to a feeling of stuffiness similar to a head cold.
Menstrual synchrony and smell Armpit swabs taken from donor women at a certain phase in their menstrual cycle and wiped on the upper lip of recipient women can advance or retard menstruation in the recipients depending upon the phase of the donor (Stern & Mc. Clintock, Nature (1998) 392, 177 179): They found that odourless compounds from the armpits of women in the late follicular phase of their menstrual cycles accelerated the preovulatory surge of luteinizing hormone of recipient women and shortened their menstrual cycles. Axillary (underarm) compounds from the same donors which were collected later in the menstrual cycle (at ovulation) had the opposite effect: they delayed the luteinizing hormone surge of the recipients and lengthened their menstrual cycles. By showing in a fully controlled experiment that the timing of ovulation can be manipulated, this study provides definitive evidence of human pheromones.
Attractiveness of men's faces in relation to women's phase of menstrual cycle n n In between subjects studies on two groups of women of the same age, we show that women assess male's facial attractiveness differently in the follicular (F) and luteal (L) phases. In the high conception risk phase (F), women tended to give higher scores to male faces than when they were in the luteal phase. During the five first days of the cycle, i. e. when the estrogen level is still low, women assessed men's facial attractiveness relatively highly. We suggest that it is progesterone in the luteal phase that is responsible for lower attractiveness assigned then to male faces. We also tested which anthropometric facial traits or indices influence male attractiveness. We found that assessments of attractiveness were correlated only with mouth height (positively) and the angle between the middle of the mouth and the middle of the eyes (negatively). Danel D, Pawlowski B, Coll Antropol. 2006 Jun; 30(2): 285 9
Smell of fear Dogs and horses can smell fear in humans. Work by Denise Chen (Chen & Haviland Jones, Physiology and Behaviour 1999; 68: 241 250) has demonstrated the ability of underarm odour to influence mood in others. Karl Grammer, in Vienna, has recently demonstrated that the smell of fear can be detected (by women) in the armpit secretions of people who watched a terrifying film (Ackerl, Atzmueller & Grammer, Neuroendocrinol Lett 2002; 23(2): 79 84). The implication of this work is that a chemical signal is secreted in sweat which communicates the emotion.
Pheromones In many animals, the sense of smell is used for communication. For example, insects such as ants and termites and vertebrates such as dogs and cats communicate with each other by secreting and detecting odorous signals called pheromones – especially to signal sexual receptivity, danger, territorial boundaries, and food sources. We humans seem to use the sense of smell primarily in conjunction with taste to seek and sample food, but some evidence exists to suggest that people may also use sexual pheromones as well as pheromones that help us identify family members by smell. For more information: n Video “Sweaty T-Shirts and Human Mate Choice” for an evolutionary perspective on pheromones
Fragrance Effects Research suggests that pleasant scents may trigger pleasant moods and give a boost to workers’ performance. Social psychologist Robert Baron, who has studied these fragrance effects, has patented and is marketing a device that emits pleasant scents. Called PPS (Personal Productivity/Privacy System) it combines fragrance release with a white noise generator and an air filter. After testing dozens of smells, Baron found that lemon and light floral had broad appeal (pine was the least popular odor), and is marketing discs producing these odors with the PPS. On a much larger scale, Shimizu Corporation has also patented an “odor delivery” for commercial buildings. For example, it pumps a citrus odor through an office building’s ventilation ducts every two minutes. “The fragrance sense can be fundamental to controlling conditions for office workers, ” says Junichi Yagi, a representative for Shimizu. He cites a month long study of Japanese keypunchers in which those who inhaled a lemon aroma make 54 percent fewer errors than those who sniffed plain air. While the citrus odor seemed to make people more alert, other smells, such as spiced apple, seemed to aid relaxation.