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UA ECOL 437 - Vertebrate Physiology

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Lecture 08, 18 Sept 2003Chapters 7 (and 8?)Vertebrate PhysiologyECOL 437University of ArizonaFall 2003instr: Kevin Boninet.a.: Bret PaschVertebrate Physiology 4371. Nervous System (CH7, CH8)2. Term paper topic and annotated references due3. Exam Thurs next week -old exam on website -review sheet later today7-24 Randall et al. 2002Enhancing Receptor Sensitivity- Lateral Inhibitione.g., improvetouch sensitivityand visual acuity(edges especially)7-14 Randall et al. 2002Ch 7 Sensing the EnvironmentExternal Chemoreception (Taste and Smell)-Taste~ direct contact-Smell~ distant signal source-Chemoreception very sensitive-Bombyx moth antenna example:Male responds to femalepheromone at low [ ] of1 molecule in 1017 !Taste Chemoreception-Taste1. Salt2. Sour3. Sweet4. Bitter5. Umami (“savory” or ”meaty”)SaltySourSweet4-5 qualities:Usually oral cavitySome fish fins!Differing ReceptorProperties7-17 Randall et al. 2002Taste-Generate AP’s but no axons-1º afferent neurons in facial,glossopharyngeal, and vagus nerves- microvilli- basal cells giverise to new receptorcells every 10 days7-16 Randall et al. 200210-14 Silverthorn 2001human10-15 Silverthorn 2001Smell/ Olfaction-1 Nasal Cavity-turbinates (↑s.a.)-2 Vomeronasal organ-usually conspecificcommunication7-19 Randall et al. 20027-16 Randall et al. 2002Smell/ Olfaction-Nasal and Vomeronasal:-Epithelial tissue origin-Cilia or Microvilli covered in mucus-Receptor proteins with 7-transmembrane helices-Coupled to G-protein cascade7-21 Randall et al. 2002Smell/ Olfaction- Nasal and Vomeronasal:-Thousands of receptor proteins-but different for nasal and vomeronasal-Receptor cells contain axons- Glomeruli in olfactory bulb/accessory olfactory bulb7-21 Randall et al. 2002Mechanoreception- Several Types:1 Undifferentiated nerve endings in connective tissue2 More specializede.g., Pacinian Corpusclee.g., Muscle stretch receptors3 hairlike sensory receptorsActivated by stretch ordistortion of plasmamembraneMechanoreception- Hair Cells in cupulaone Kinocilium (or none)many stereociliae.g.,-lateral line system in fish and amphibians(motion/electricity)-hearing and equilibrium7-24 Randall et al. 20027-25 Randall et al. 2002Hearing and Equilibrium- Both are functions of the earEquilibrium:2 chambers Sacculus Utriculus w/ 3 semicircular canals in three perpendicular planesThese three planes can detect movement in anydirection as endolymph moves and cilia are bentSacculus and Utriculus also contain patches of hair cells that detect position relative to gravity via otoliths7-26 Randall et al. 20027-27 Randall et al. 200210-24 Silverthorn 2001Hearing (in a nutshell…1)- external ear funnels sound- sound is oscillating air pressure- funneled to tympanic membrane (eardrum)- auditory ossicles transfer sound across air-fluid boundary to oval window (another membrane)- [auditory ossicles are malleus, incus, stapes]- tympanum area 19x oval window area= amplificationHearing (in a nutshell…2)- cochlea is fluid filled chamber on other side of oval window and it contains hair cells- hair cells in cochlea bathed in endolymph (high in K+)- when cilia bent, ion channels for K+ open and cell depolarizes, causing transduction- (skipped a lot of detail about the cochlea)- different hair cells (and location in cochlea) for different frequencies of sound7-27 Randall et al. 2002VisionDisappearing Head Trick!Disappearing Head Trick!Vision- light is focused by cornea to create an image on the retina- refraction by cornea (85%) and by lens (15%)- alter focal length by altering shape and curvature of lens (zonular fibers and ciliary muscle ‘sphincter’)- binocular convergence (both eyes on same part of retina)LIGHT INTENSITY- pupil for variable aperture via iris and radial muscleFOCUS7-34 Randall et al. 20027-37 Randall et al. 200210-27 Silverthorn 200110-29 Silverthorn 2001Out of focusdistantcloseVision- sclera white tough outer layer- choroid lots of blood vessels- pigment layer with photoreceptors- fovea where highest acuity and highest # cones-(visual streak?)- photoreceptors (rods and cones)-Transduce photons (light) into electrical signal- rhodopsins (visual pigments) opsin (7-transmembrane lipoprotein) plus retinal (absorbs photon)~ANATOMYTRANSDUCTIONVisionRods andConesReceptor Cells-Dim light, low resolution-Bright light, high resolution7-38 Randall et al. 200210-27 Silverthorn 2001Rods andConesRhodopsins (visual pigments)-located in stacked lamellaeMembraneshyperpolarize inresponse to lightNa+ ‘dark current’When light hits,the Na+ currentinto the cell isstopped andmembranehyperpolarizesstopping release ofNT7-39 Randall et al. 2002Rhodopsin mechanism:cis-trans isomerization of retinal moleculeChanges conformation of opsinmolecule and therefore initiatestransductionactivated7-43 Randall et al. 2002Activated retinal changes conformationof opsin molecule (opsin and retinalseparate) and initiates transductionG-proteinamplificationNeed toreconstitutethe rhodopsin(night blindness)7-45 Randall et al. 20027-44 Randall et al. 2002Rod and Cone detailsAction spectrum (where absorb light)3 (e.g., humans, fish)-5 (e.g,. birds)different photopigmentsDifferent opsins, same retinalSensitivity vs. AcuityPorphyropsins (differentretinal) seem better thanrhodopsins in freshwater10-35 Silverthorn 2001Physiology PlayersTheatre Slam-3 competing casts-Judge(s) -accuracy -enthusiasmActors:1. Photon 4. Transducin 7. Ion channel2. Retinal 5. PDE 8. Cation (Na+)3. Opsin 6. cGMPAct IPhoton enters stage right. Other players assembledwithin or near membrane. …photo transduction...Dark current reduced as curtain closes.7-49 Randall et al. 2002Red vs. Green


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