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PSYB51 chapter 14 and 15.docx

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Maydianne Andrade

PSYB51- Chapter 14 Taste - Olfaction and gestation are often grouped together as the chemical senses - in terms of physiology , these two sensory systems are in some ways quite similar - taste serves the most specific function of any of the senses: it controls which chemicals we need to ingest because they are nutritious and which we need to spit out because they may be poisonous Taste vs. Flavour -to the early Greeks, sensations perceived from foods and beverages in the mouth were tastes ands sensations perceived by sniffing were smells - but food molecules are almost always perceived by both our gustatory and our olfactory systems - the molecules we taste are dissolved in out saliva and passed over the taste receptors our taste buds - when we chew and swallow our food, other molecules are released into the air inside our mouths and forced up behind the palate into the nasal cavity where they contact the olfactory epithelium and stimulate our olfactory receptors -retro nasal olfactory sensations: the sensation of an odour that is perceived when chewing and swallowing force an odorant in the mouth up behind the palate into the nose - Such odour sensations are perceived as originating from the mouth even though the actual contact of odorant and receptor occurs at the olfactory mucosa - flavour: the combination of true taste ( sweet, salty, sour, bitter) and retro nasal olfaction - foods are perceived by the somatosensory system by touch, temperature, and pain receptors in the tongue and mouth - some of these sensations have protective functions: such as the burn of acid, protection from things that might damage your stomach - somatosensations also provide information about the nature of foods…example, fattening foods are oily etc… Localizing Flavour Sensations - flavour seems to come from the mouth because of the tactile sensations of chewing and swallowing that occurs in the mouth - only things like wasabi give off volatile chemicals that run all the way to your retro nasal passage because they activate the pain receptors - chorda tympani: branch of cranial nerve VII - carries taste info from the anterior mobile tongue - leaves the tongue with the lingual branch of the trigeminal nerve and then passes through the middle ear on its way to the brain - Study: subjects had their chorda tympani anesthetised with lidocaine while they tasted yogurt - they reported a blueberry sensation due to retro nasal olfaction, they said it came from right side of mouth - the intensity of the blueberry sensation was reduced, and this intensity was reduced even further when both taste nerves were blocked - the brain processes odours differently, depending on whether they come from the mouth or through the nostrils - need signals from the outside world to tell us where an odour is coming from, input from the olfactory receptors cannot be routed to the proper brain area to connect the smell sensation with the food stimulus - sugar ( increase in sweetness) will increase the perceived olfactory sensation of something. - so if you want to make people buy pear juice, adding sugar will make the smell of it more intense. Anatomy and Physiology of the Gustory system - Taste perception: - Chewing breaks down food substances into molecules - dissolved by saliva - molecules flow into a taste pore that leads to the taste buds embedded in structures called papillae -papillae: give tongue its bumpy appearance - types that have taste buds: fungi form, foliate, and circumvillate - types that do not have taste buds: filiform papillae ( smallest type) - the tongue is the “retina of the mouth” - each taste bud has a lot of taste receptor cells: cells within the taste bud that contain sites on their apical projections that can interact with taste stimuli. These sites falls into two major categories: those interacting with charged particles and those interacting with specific chemical structures - the taste receptor responds to a limited number of molecule types - when one of its preferred molecules makes contact with it, it produces action potentials that send information along one of the cranial nerves to the brain Taste Buds and Taste Receptor Cells - Each taste bud is a cluster of elongated cells - the tips of some the cells, the taste receptor cells, end in slender microvillus - microvillus contains the sites that bind to taste substances - they are extensions of the cell membrane, not tiny hairs - in fungi form papillae, the taste nerve fibres that enter the taste buds branch so that an individual cell can be innervated by more than one taste fiber - an individual taste fiber can be innervated more than one cell - taste receptors have a limited life span: about 10 days they die and are replaced by new cells - this replaces allows the taste system to recover from any damage- which is why our taste system is still robust even in old age - nerve fibers are able to select the cells with which they will synapse so that the message they convey remains stable, even though the receptor cells are continually replaced - tastant: any stimulus that can be used - the mechanisms that permit a taste cell to recognize a taste stimulus, contacting its microvili can be divided into two large categories: 1. One class of tastants is made up of small, charged molecules that taste salty or sour. Small openings, called ion channels, in microvili membranes allow some types of charged particles to enter cells but bar others - when the charged particles in salty and sour foods enter salty and sour receptor cells, the cells signal their tastes 2. Tastants that produce sensations that we label as sweet or bitter are perceived by a mechanism similar to that in the olfactory system - using G proteins coupled receptors(GPCR)- they wind back and forth across microvillus membranes and when a particular tastant molecule “ key” is fitted into the “lock” portion of a GPCR on the outside of the membrane, the portion of the GPCR inside the cell starts a cascade of molecular events that eventually causes an action potential to be sent to the brain Taste Processing in the central nervous system - after leaving the taste buds through the cranial nerves, gustatory information travels through way stations in the medulla and thalamus before reaching the cortex - the primary cortical processing area for taste- the part of the cortex that first receives taste info- is the insular cortex - insular cortex: the primary cortical processing area for taste- the part of the cortex that first receives taste information - The orbit frontal cortex receives projections from the insular cortex - some of these ^ neurons are multimodal - they respond to temperature, touch, smell, taste suggesting that it may be an integration area - inhibition is used to protect our whole mouth perception of taste in the face of injuries to the taste system - out brains receive taste input from several nerves- releases inhibition so that damage is not entire - localized taste damage though is often accompanied by phantom taste sensations which is as if the release of inhibition permits even noise in the nervous system to be perceived as a taste -patients with a serious oral pain disorder were shown to have localized taste damage as well - women who have taste damage are more likely to suffer from severe nausea and vomiting during pregnancy…also people with cancer who undergo chemotherapy that damages taste system experience same thing…coughing, gagging etc.. The Four Basic tastes: - salty, sour, bitter, sweet SALTY - made up of two charged particles: a cation and an anion - common salt is NaCl - sodium must be available in relatively large quantities to maintain nerve and muscle function and a loss of body sodium is fatal - if you don’t eat so much salty foods, once you do eat something salty…it seems more salty than it is - increased preference for salty snacks among college students whose mothers had experienced moderate to severe morning sickness during pregnancy SOUR - The taste quality produced by the hydrogen ion in acids - sour is the taste of acids - at high concentrations acids will damage both external and internal body tissues BITTER - The human genome project revealed a multigene family responsible for about 25 different bitter receptors - The bitter genes are located on three different chromosomes: 5, 7, 12 - quinine, which is used to treat malaria, is one example of a bitter compound - the diversity of receptors for bitterness enables species or individuals in a given species to have varying responses to an array of bitter compounds - compounds that taste bitter tend to be poisonous - Some are good for us -Adenosine monophosphate:bitter inhibitor that is natural in mother’s milk -sensitivity to bitterness intensifies during pregnancy and diminishes in menopause SWEET - evoked by sugars - artificial sweeteners don’t actually taste like sugar Survival Value of Taste - sense of smell helps us identify objects in our environment - gustatory system responds to a fixed and much smaller set of molecules - each of the four basic tastes is responsible for a different nutrient or anti nutrient and has evolved according to its purpose - bitterness a type of poison detector Chapter 15: Spatial Orientation and the Vestibular System - the vestibular system: sometimes called the vestibular labyrinth - set of specialized sense organs located in the inner ear right next to the cochlea - These organs sense motion of the head, as well as the orientation of gravity and make a predominant contribution to our sense of tilt and out sense of self motion - spatial orientation: a sense comprised of three interacting sensory modalities: our sense of linear motion, angular motion, and tilt - the vestibular “sixth sense” provides fundamental contributions that are often overlooked - it does things like, contributing to clear vision when we move and helps us maintain balance when we stand - people report cognitive deficits when it fails - but it remains unaware until it completely stops working - before, this system was thought of to be just the entrance to the cochlea - many of the responses evoked by this system are reflexive and linked to the outputs of other sensory systems - ex: at higher frequencies of motion, you should notice that each fingertip stays in focus more readily and at higher speeds when you move your head than when you move your hand - you can compensate for head movement more readily than hand movement because of a vestibulo ocular reflex Modalities and Qualit
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