Lecture 8: Chemical Senses
Lecture 8: Chemical Senses Bil 268
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Date Created: 02/24/15
BIL 268 02122015 Lecture 8 Chemical Senses I Gustation Five basic tasti There are ve basic tastes saltiness sourness sweetness bitterness and umami The taste of deliciousness for umami Sugars like fructose and arti cial sugars are for sweetness and ions like potassium and magnesium are for bitter Taste Organs If you stick your tongue out and look at it in the mirror you can see the surface of it If you open your mouth the taste sensitivity is different 0 Maybe a portion of your tongue is especially sensitive to bitterness Tip of the tongue is more sensitive to sweetness while back of the tongue is more sensitive to bitterness The sides of the tongue are sensitive to saltiness and sourness The palate and the epiglottis are evolved for sensation and are not as strong as your tongue Tongue has the taste receptor cells The taste organs what are they 0 The tongue isn t entirely at It has bumps 0 These bumps are called papillae Leaf shaped papillae are foliate papillae You can nd receptor cells in the taste bud along with basal cells marked in green on the PowerPoint Some of the taste receptor cells are innervated by the nerve bers The receptor cells are regenerated and they have a short life span 2 wks at which point the basal cells develop into the receptor cells 0 Same thing is true for the olfactory receptor cells When you are born you have a xed number of auditory receptor cells 0 Which is why as you get older you have hearing loss Sensory Transduction Very important concept Applied to taste and smell along with hearing It s basically the process to convert a natural stimulus into an electrical signal at the receptor cell level If you have sugar directly stimulated to the brain directly you will not get any taste at all 0 Your brain cannot take the natural stimulations You must have something at the peripheral level to convert natural stimulation unto signals that can be recognized by the brain Refer to the schematic drawing in the ppt When you re recording from the membrane you re recording the Action Potentials yellowish box Taste receptor cells are capable of conducting action potentials even though they are receptor cells Transduction Mechaniw lonic processes underlying the basic tastes You need to know the ow chart and pay attention to whether ion channels or Gprotein coupled receptors are used If you have a drop of table salt on your tongue the sodium ions will go in via diffusion Amiloride o The positive ions going in will cause depolarization of the cell membrane which in turn will effect the voltagegated sodium channels and cause them to open 0 Synaptic Transmission will occur Sourness Increasing the Hydrogen ion concentrations 0 The H ions getting in will cause depolarization The potassium ion channels are open 0 The in ux of the hydrogen ions will cause the potassium ion channels to close It will cause depolarization which in turn will open voltage gated ion channeb Sourness looks at acidity and pH Sweetness Bitterness and Umami All three use Gprotein coupled receptors The taste binds to the receptor When the lP3 concentration is high it will cause the release of intercellular calcium into the cytosol which will sort of depolarize Different receptor cells have different receptors Taste Receptors There are three different taste receptors and two families of genes 0 One is called T1R gene family and the other is T2R o Transmembrane receptors that can generate about 30 membrane proteins depending on the different kinds of proteins 0 Different combinations will give you different taste sensations The T2R family has different shapes and groove patterns The sweet and umami receptors are from T1R Overall the one receptor contains two proteins Capsaicin Why do hot peppers taste Kind of like something is burning on your tongue In the hot peppers you have the capsaicin which can activate the thermal nociceptor pain 0 Burning pain The heat opens the ion channel causing the in ux of the cation Neural Coding of Taste There are two theories labeled line and population coding Labeled line is found in invertebrates The way the system is designed is that the receptors are tuned to one type of chemical Mwcom Type III receptors if isolated will only respond to salty and sour 0 However if you have the entire cell the cell will respond to all the different types of taste buds Can be recorded in vitro and in vivo The ATP released by the type II receptor cells will bind to the receptor Central Taste Pathways Sensory neurons go to different levels in the brain and eventually reach the cortex cells Gustatory cortex Impairment of taste ageusia ll Olfaction Pheromones are body odors we all have them o It is basically the chemical released in response to the same species o It can be seen as a mode of communication for the rodents Relegated to reproduction or territorial ghts Identi cation and aggression Smell Organ If you look at the medial view you ll see our nose chamber The dorsal wall has olfactory epithelium which has many receptor 0 If you make a cut you can nd the receptor cells along with the basal cells in addition to supporting cells 0 The receptor cells go and die 4 8 wks The basal cells regenerate into the new smell receptor cells The function of the supporting cells is that you need to have a layer of mucus that is produced by the supporting cells The taste receptor cells are neurons because they look like neurons and they function like neurons The cilia found in the mucus layer generate action potential which travels to the brain The receptor cells go directly to the brain quite unique The axon cells of the receptor cells innervate the brain Olfactory Transduction Looking at the tip of the cilia you can nd gprotein coupled receptors 0 ATP is converted to cAMP cAMP opens the ion channels and are also referred to cAMP gated channeb 0 Causes an in ux of positive ions which leads to depolarization 0 You cannot generate AP until the threshold is reached The in ux of positive ions will open the chlorine channel which will cause Calcium gated ion channels cells These are different from normal neurons 0 The outside concentration for chlorine is higher in normal neurons 0 It s the opposite in these neurons 0 The IC side has a higher concentration of chlorines The glomerulus there are three receive input from many receptor 0 In each glomerulus you can nd many synapses containing axons of receptor cells and dendrites of secondary olfactory neurons The glomeruli sort out the information sent to them Refer to ppt for the diagram of the Odor map Your different odors are mapped along the olfactory bulb Neural Coding of Smell Schematic drawings in ppt You can count the number of action potentials Temporal coding is for insects and not humans 0 By looking at the pattern of action potentials in time you ll see that the ring path in time is different Olfactory Maps You need to have voltage sensitive dye to label the olfactory bulbs When the dye is absorbed the receptor cells also have the dye You can play around with different stimulations and then look at the images caused which will cause the dye to emit light 0 The microscope will detect the pattern of the emissions so that you can form a map corresponding to different stimuli Use uorescent or confocal microscope
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