Sensory Transduction Olfaction Chemoreceptors Photoreceptors Vision Olfactory bulb Olfaction Chemoreceptors Photoreceptors Vision Mechanoreceptors Audition Sensory Transduction

Direction of retinal visual processing 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 cell Horizontal cell Cone Rod Photoreceptor cells

Rhodopsin in the light: retinene changes shape Back of retina Cells of pigment layer Phototransduction Cone Rod Outer segment Discs Disc Outer segment Mitochondria Inner segment Inner segment Nuclei Light absorption Retinene Dendrites of bipolar cells Opsin Synaptic terminal Synaptic terminal Enzymes Rhodopsin in the dark: retinene in 11-cis form (inactive) Rhodopsin in the light: retinene changes shape to all-trans form (active) Front of retina Direction of light 11-cis form of retinene all-trans form of retinene

LIGHT DARK Cells of pigment layer Cone Rod Discs (Absorption) DARK Activation of photopigment High concentration of cyclic GMP Cells of pigment layer Activation of transducin (G protein) Activates PDE (Reaction cascade) Cone Rod Takes place in outer segment Takes place in outer segment Na+ channels open in outer segment Decrease in cyclic GMP Discs Closure of Na+ channels in outer segment Membrane depolarization Outer segment (Spreads to synaptic terminal) Membrane hyperpolarization (the receptor potential) Takes place in retina Opens Ca2+ channels in synaptic terminal Inner segment (Spreads to synaptic terminal) Takes place in synaptic terminal Takes place in retina Nuclei Closure of Ca2+ channels in synaptic terminal Takes place in synaptic terminal Release of inhibitory transmitter (inhibition) Synaptic terminal Release of inhibitory transmitter Bipolar cells inhibited Bipolar dendrites (Removal of inhibition) Bipolar cells disinhibited (or, in effect, excited) Front of retina Graded potential change in bipolar cell No action potential in cell ganglion cell (If of sufficient magnitude to bring ganglion cell to threshold) Action potential in ganglion cell No action potential propagation to visual cortex Propagation of AP to visual cortex (occipital lobe) visual perception

Rods versus Cones What about adaptation? 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

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 Vibration of round window Energy dissipates Tympanic Membrane Vibrates Ossicles Vibrate Oval Window Vibrates Fluid Movement within Cochlea Vibration of round window Basilar Membrane Vibrates Energy dissipates (no sound perception) Takes place in ear 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

The Transduction Channel

What about Adaptation?

What about the Outer Hair Cells?

What about the Outer Hair Cells?

Cochlear Implants