Lecture 8 for Neurobiology
Lecture 8 for Neurobiology Bil 268
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This 3 page Class Notes was uploaded by Pooja Dave on Thursday September 29, 2016. The Class Notes belongs to Bil 268 at University of Miami taught by Dr. Zhongmin in Fall 2016. Since its upload, it has received 15 views. For similar materials see Neurobiology in Neurobiology at University of Miami.
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Date Created: 09/29/16
Neurobio Lecture 8: Chemical Senses 5 senses - vision is the most important o Taste/smell evolved first = chemical senses Gustation = taste o Phenylthiocarbamide (PTC) Arthur fox from dupont co lab PTC test = two people tasted it and felt two different things Taste gene 3 forms o Form 1/form 1 = homozygous, bitter for PTC o Form 1/form 2 = heterozygous, somewhat bitter o Form 3/ form 3 = homozygous, not bitter o 5 basic tastes Saltiness, sourness, sweetness, bitterness, and umami o Taste organs Tip of tongue = sweetness, more receptor cells for sweetness Back of tongue = bitterness Sides of tongue = saltiness and sourness Pharynx and epiglottis = at back of tongue/throat, some sensitivity to taste Papillae Foliate = looks like leaf Vallate = looks like volcano Fungiform = looks like mushroom Many taste buds for 1 papillae = contain taste receptor cells o Interface between brain and environment o Designed specifically for taste chemical signals o Receptor cells last only for 2 weeks = basal cell generates new receptor cells (doesn’t apply to auditory receptor cells, one reason for hearing loss with age) Receptor potentials o Can generate AP if strong enough, but normally does not fire AP Receptor vs neuron = need taste molecule to activate, sensory transduction o Sensory transduction Convert natural signal to chemical signal by the receptor cells Capable of causing membrane potential change that leads to depolarization and release of NT etc. gustatory afferent axons – detect AP o know flow charts – membrane proteins o transduction mechanisms tastants ion channels or g protein coupled receptors saltiness uses ion channel amiloride sensitive sodium channel – open all the time voltage gated Ca and Na channel - depolarization sourness uses ion channel h gets in through amiloride sensitive closes potassium channel reach threshold of voltage gated Ca and Na sweetness/bitterness/umami use g protein coupled receptors g protein activated phospholipase C triggers intracellular Ca release leads to depolarization and open voltage gated cation channel o Taste receptors T1R family (umami and sweet) = two receptors in combination T2R family (bitter) o Capsaicin In hot pepper Activates thermal nociceptor = heat pain receptor Causes influx of cations o Neural coding of taste Labeled line - insects Each receptor is unique in dna codes A lot of energy to design unique receptor cells Population coding - human Recording from one receptor cell Relative sensitivity to different tastes in the receptor Instead of having individual pieces of code for each receptor, use brain to analyze the response received – moves job from PNS to CNS o Taste receptor cells Type II – for bitter/sweet/umami, not innervated with sensory neurons, release ATP NT to bind to receptor in Type III to activate sensory neurons Type III – for salty/sour, presynaptic cell innervated with sensory neurons o Central taste pathways Localized lesions -> ageusia Loss of taste perception Ipsilateral – left side of tongue to left side of brain Olfaction = smell o Pheromones Smell = mode of communication Important signals Reproductive behavior Territorial boundaries Identification aggression o smell organ olfactory epithelium receptor cells and basal cells o receptor = neurons that generate AP, die then basal become receptor cells supporting cells = produce mucus that cover olfactory epithelium receptors are directly connected to the brain by olfactory bulb o olfactory transduction binds to g protein coupled receptor that triggers cAMP triggers Ca channel to open ca concentration is high = activates chloride channel that causes it to leave depolarization by decrease in negative inside o central olfactory pathways glomerulus – on olfactory bulb that connects terminus of receptor to dendrites of olfactory neuron random mapping to organized mapping in glomerulus = odor map o neural coding of smell population coding temporal coding locust smell receptor o give apple smell to locust and receptor cells are set off at different times onset = responds to start of stimulation sustained = responds to continued stimulation buildup = gradually increase as stimulation continues off set = during stimulation no AP inhibition = hyperpolarizes during stimulation o Olfactory maps = Sensory maps Voltage sensitive dye o
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