Psyc 6 week 4
Popular in Introduction to Neuroscience
Popular in Psychology (PSYC)
This 5 page Class Notes was uploaded by Sabrina Straus on Monday October 3, 2016. The Class Notes belongs to PSYC 6 at Dartmouth College taught by Catherine Cramer in Fall 2016. Since its upload, it has received 5 views. For similar materials see Introduction to Neuroscience in Psychology (PSYC) at Dartmouth College.
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Date Created: 10/03/16
3. 09-30-16 Intro to Neuro class notes REVIEW -smooth goes myelinated axon } faster than temp -finer 2point : smaller receptive field -study dermatome Dorsal: touch vibration Cross in medulla Anterolateral: pain and temperature Immediate cross -decussate at different points CLASS NOTES CHEMICAL SENSES I. Gustation A. Anatomy Papillae- bump Has receptors that can transduce all of the tastes taste buds-has cell where transduction occurs Taste dissolves in saliva and is taken in free nerve ending sites facial & glossopharyngeal nerves Receptor cell->glossopharyngeal nerve-> facial nerve-> gustatory nucleus->brainstem->thalamus gustatory nucleus primary gustatory cortex B. Processing of primary tastes (salty, sour, bitter, sweet, umami) transduction at ion channels Salty: Na+ enters channel and depolarizes cell (graded potential opens voltage gated sodium channel and Ca2+ flows into open vesicle) Sour: H+ flows in and inhibits potassium channels to depolarize cell (Na+ and Ca2+ go in and fires action potential) transduction involving second messengers Bitter, sweet, amami: like metabotropic because use G-protein coupled receptors (ca2+ is stored in the cell and is released which causes Na+ to flow in which stimulates ATP and causes AP) } no release of neurotransmitter** After transduction->gustatory axon Different cells respond to different tastes Some element of labeled lines population coding-pattern of firing C. Taste (only the gustatory part) vs flavor (taste and smell) II. Olfaction A. Anatomy air->turbinates olfactory mucosa->dissolves and goes to epithelial->receptors->bulb (glomerulus->mitral cell->bulb->tract (in central nervous system)->synapses in tubercle->thalamus and orbitofrontal cortex and to other areas like hypothalamus or amygdala and prepyriform cortex)) In cilia: odor-> g protein w/ ATP -> cAMP -> in Ca2+ and a+-> depolarize and out of Cl- -> action potential -> olfactory receptor -> bulb olfactory epithelium olfactory bulb Glomeruli-composed of inputs from one type of receptor and odor B. Models of initial processing transduction receptor specificity C. Central projections amygdala hypothalamus prepyriform (primary olfactory) cortex = mixing thalamus and orbitofrontal (secondary olfactory) cortex D. Population coding spatial vs temporal Chapter Notes Chapter 8: Chemical Senses ~help identify nourishment, noxious substances, or suitability of a potential mate and determine flavor -Taste : gustation ● Basic tastes: salty, sour, sweet, bitter (poisons), and delicious (defined by the savory taste of monosodium glutamate:MSG) ○ Organs of taste: tongue (tip=sweetness/back=bitter/sides=salty+sour), palate, pharynx (receives odors and passes to nasal cavity where olfactory receptors detect), and epiglottis ■ Tongue: has papillae (bumps that have taste buds which have taste receptor cells a taste pore and basal cells all connecting to gustatory afferent axons / ● Need a threshold concentration ○ Taste receptor cells: chemically sensitive part of taste receptor is small membrane } apical end ■ apical end: Have thin microvilli that project into taste pore ■ Taste poor: small opening on tongue where taste cell is exposed to contents in mouth ■ Not neurons but do form synapses w/ gustatory afferent axons @ bottom of taste bud ■ Make electrical and chemical synapses onto basal cells which synapse onto sensory axons ■ Undergo constant cycle of life (2 weeks)} depends on sensory nerve ■ Receptor potential: when chemical activates receptor and depolarizes-> taste receptors fire action potentials-> voltage gated calcium channels open and Ca2+ enters cytoplasm (triggering release of transmitter molecules) -> postsynaptic sensory axon communicate to brain stem ● Sour + salty: release serotonin onto gustatory axons ● Sweet + bitter + umami: release ATP ○ Mechanisms of taste transduction ■ Transduction: process by which an environmental stimulus causes an electrical response in a sensory receptor (1) directly pass through ion channels (salt and sour) (2) bind to and block ion channels (sour), or (3) bind to G-protein-coupled receptors in the membrane that activate second messenger systems that, in turn, open ion channels (bitter, sweet, and umami). ■ Saltiness: NaCl ● Taste cells use a Na+ selective channel (sensitive to amiloride) + generally stays open } diffusion -> depolarization -> voltage-gated sodium and calcium channels open near synaptic vesicles to trigger the release of neurotransmitter molecules ■ Sourness: high acidity -> protons ● H+ can bind and block K+ selective channels -> depolarization ■ Bitterness: relies on T1R and T2R ● G protein coupled taste receptors -> stimulate enzyme to increase production of intracellular messenger-> activates ion channel Na+ and Ca2+ -> activate special membrane channel that allows ATP to leave the cell as a synaptic transmitter, activating purinergic receptors ● Diamers ■ Sweetness: all dimers of G-protein-coupled receptors ● Requires T1R2 and T1R3 ● Activates same second messenger as bitter receptors but on different taste cells and connect to different gustatory axons so messages are delivered to the central nervous system along different transmission lines ■ Umami (amino acids): same as sweetness except ● T1R1 and T1R3 ● Specific taste cells ○ Central taste pathways : taste buds->primary gustatory axons->brain stem->thalamus->cerebral cortex ■ Facial nerve: axons from anterior ⅔ tongue+palate to cranial nerve ■ Glossopharyngeal nerve: axons from posterior ⅓ tongue ■ Vagus nerve: from throat (glottis, epiglottis, and pharynx) synapse within gustatory nucleus ■ Path to neocortex via thalamus is a common one for sensory info ● Neurons of gustatory nucleus synapse in ventral posterior medial (part of thalamus that deals w/ sensory info) -> sends axons to primary gustatory cortex ● Pathways are ipsilateral to cranial nerves ● Gustatory info is distributed to hypothalamus+telencephalon (of limbic system) ○ Neural coding of taste ■ Taste line ■ one axon may combine the taste information from numerous taste cells ■ Mixing of taste info ■ Population coding: responses of a large number of broadly tuned neurons are used to specify the properties of a particular stimulus ■ Other senses also help out like smell, temperature, etc -Smell : olfaction ● Pheromones:chemicals released by the body-> important for reproductive behaviors ○ Organs of smell ■ Olfactory epithelium: thin sheet of cells high up in the nasal cavity ● Olfactory receptor cells: sites of transduction } genuine neurons w/ axons that penetrate into the central nervous system ○ Cycle (4-8 weeks) ● Supporting cells: help produce mucus ○ Odorants: dissolve in mucus layer before they reach receptor cells ● Basal cells: source of new receptor cells ○ Olfactory Receptor Neurons: have a single dendrite that ends at the epithelium and there are a lot of cilia in mucus ■ Odorants: dissolved in mucus + bind to surface of cilia and activate transduction ■ Unmyelinated axon: on opposite side of olfactory receptor cell} constitute olfactory nerve ■ Cribriform plate: small cluster of axons penetrate this boe then go to olfactory bulb ■ Olfactory transduction: transduction molecules are located in thin cilia ● odorants->receptors->G-protein->activate adenylyl cyclase->form cAMO->bind to cyclic nucleotide-gated cation channel->opens and influx of Na+ and Ca2+ and Cl- (amplifies receptor potential) ->depolarization ● Strength of smell usually fades because the response of the receptor cell itself adapts to an odorant within about a minute } adaptation ■ Olfactory receptor proteins: G-proteins ■ cAMP-Gated channels: channels in cilia respond directly to cAMP ● Also used for visual transduction ● Population coding scheme ○ Central Olfactory pathways: responds to all info from olfactory epithelium (population code) and use it to classify odors ■ Olfactory receptor neurons send axons into two olfactory bulbs ■ Bulbs are full of neural circuits w/ various neurons ● Glomeruli: has endings of axons which converge and terminate on dendrites of second-order neurons ■ Olfactory cortex: target of output axons of bulbs (whereas all other sensory systems first pass thru thalamus) ○ Spatial and temporal representations of olfactory information ■ Olfactory Population Coding: combination of responses ■ Olfactory maps: arrangement of neurons that correlates w/ certain features of the environment ● Neurons in particular places respond to particular smells ● Spatial patterns ■ Temporal coding ● Slow action potentials ● Timing helps determine smell -Chemoreceptors : report subconsciously and consciously about internal state
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