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Sensory Transduction Chemoreceptors Photoreceptors Mechanoreceptors Olfactory bulb Audition Olfaction Vision Anatomy of the Retina Direction of light Pigment layer Choroid layer Direction of retinal visual processing Sclera Front of retina Back of retina Fibers of the optic nerve Ganglion cell Amacrine cell Bipolar Horizontal cell cell Cone Rod Photoreceptor cells Back of retina Cells of pigment layer Cone Outer segment Inner segment Phototransduction Rod Discs Mitochondria Outer segment Nuclei Inner segment Disc Light absorption Retinene Synaptic terminal Dendrites of bipolar cells Front of retina Direction of light Opsin Synaptic terminal Rhodopsin in the dark: retinene in 11-cis form (inactive) 11-cis form of retinene Enzymes Rhodopsin in the light: retinene changes shape to all-trans form (active) all-trans form of retinene LIGHT (Absorption) DARK Activation of photopigment High concentration of cyclic GMP Na+ channels open in outer segment Takes place in outer segment Activation of transducin (G protein) Activates PDE Cells of pigment layer Cone Rod Discs Membrane depolarization Takes place in outer segment Opens Ca2+ channels in synaptic terminal Release of inhibitory transmitter Takes place in synaptic terminal Outer segment Membrane hyperpolarization (the receptor potential) Nuclei (inhibition) Bipolar cells inhibited Decrease in cyclic GMP Closure of Na+ channels in outer segment (Spreads to synaptic terminal) Takes place in retina (Reaction cascade) Bipolar dendrites Inner segment Synaptic terminal (Spreads to synaptic terminal) Takes place in synaptic terminal Closure of Ca2+ channels in synaptic terminal Release of inhibitory transmitter (Removal of inhibition) Bipolar cells disinhibited (or, in effect, excited) Front of retina No action potential in cell ganglion cell No action potential propagation to visual cortex Graded potential change in bipolar cell (If of sufficient magnitude to bring ganglion cell to threshold) Action potential in ganglion cell Propagation of AP to visual cortex (occipital lobe) visual perception Takes place in retina Rods versus Cones Properties of Rod and Cone Vision RODS CONES 100 M per retina 3 M per retina Vision in shades of gray Color Vision High Sensitivity Low Sensitivity Low Acuity High Acuity Night vision Day vision Much convergence in retina Little convergence in retina More numerous peripherally Concentrated in fovea What about adaptation? Color Vision Anatomy of the Auditory System The Middle Ear and Cochlea APEX: Wider, more flexible end of basilar membrane (vibrates best with low-freq) BASE: Narrower, stiffer end of BM near oval window (vibrates best with hi-freq) The Traveling Wave QuickTime™ and a Cinepak decompressor are needed to see this picture. The Organ of Corti (Stereocilia) Outer hair cells Tectorial membrane Inner hair cells Supporting cell Nerve fibers Basilar membrane The Hair Cell Potential SOUND WAVES Tympanic Membrane Vibrates Ossicles Vibrate Oval Window Vibrates Vibration of round window Fluid Movement within Cochlea Energy dissipates (no sound perception) Basilar Membrane Vibrates Closure of Ca2+ channels in synaptic terminal Hair cell stereocilia bend as the movement of the basilar membrane displaces them in relation to the overlying tectorial membrane in which they are embedded. Graded potential change in bipolar cell Graded potential change in hair cell Action potentials generated in auditory nerve Propagation of AP to auditory cortex (temporal lobe) sound perception Takes place in ear The Transduction Channel What about Adaptation? What about the Outer Hair Cells? QuickTime™ and a decompressor are needed to see this picture. QuickTime™ and a decompressor are needed to see this picture. What about the Outer Hair Cells? QuickTime™ and a decompressor are needed to see this picture. Cochlear Implants