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Sensory Systems 1 Vladimir Kefalov [email protected] 362-4376 McMillan 625 Five sensory modalities recognized since ancient times • • • • • Vision Hearing Touch Taste Smell Sensory Transduction: Sensory StimulusReceptor MoleculeTransduction Channel Receptor PotentialSpike Train or Transmitter Release Ideal Sensory Receptor Response Stimulus •Rapid response •Large amplitude •Rapid recovery •Steady baseline Important Features for Sensory Receptor Cell Function • High Sensitivity • Adaptation • Receptors code relative stimulus, not absolute size “Ionotropic versus Metabotropic” Sensory Receptors Response Stimulus A A* B A A* B* C C* Structure of Cochlea Structure of Hair Cells Deflection of Hair Cell Bundles Deflection of Hair Cell Bundle Towards Kinocilium Causes Depolarization Stereocilia Form the Apical Hair Cell Bundle Tip Links Connect Adjacent Stereocilia Scanning Electron Micrograph Transmission Electron Micrograph Where are the Transduction Channels Located? Hair Cell Transduction Channels Opened by Bundle Movement Bundle Movement K+ Ca2+ Rest Stimulated Adapted Nature of the Transduction Channels Cochlea Sound Frequency Tuning Hair Cells Frequency Tuning Voltage- and Calcium-Activated Channels Shape Hair Cell Voltage Responses Tuning Frequency and K+ Conductance Cochlea Sound Frequency Tuning Hair Cell Adaptation Involves a Calcium Feed Back Signal Bundle Movement K+ Ca2+ Rest Stimulated Adapted Myosin is the Adaptation Motor actin myosin Rate of adaptation comparable to rate of myosin movement in muscle. Adaptation is blocked by ADP, analogous to muscle rigor. Evidence for myosin in hair bundle. Possible Mechanisms of a Calcium Feed Back Signal Important Unresolved Issues • Transduction channel • Molecular basis for calcium regulation of transduction and adaptation • Other transduction complex constituents • Targeting of proteins to the hair bundle • Hair bundle development and maintenance • Possible hair cell replenishment Suggested Readings • From Neuron to Brain (IV ed.): Chapters 17 & 18 • Ionic Channels of Excitable Membranes: Chapter 8 • Sensory Transduction (Sinauer): Chapters 6-9 • Curr Opin Otolaryngol Head Neck Surg. 2008 Oct;16(5):44551.How hair cells hear: the molecular basis of hair-cell mechanotransduction. • Making an effort to listen: mechanical amplification in the ear. Hudspeth AJ. Neuron. 2008 Aug 28;59(4):530-45.
