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Sensory Systems Review 7.29/9.09 Sensory Systems Review Sensory Vision Hearing Smell Taste Touch System Signal Photon Sound wave Chemical Chemical Pressure, vibration, temperature, chemicals (pain) Encoded Color (cones) Amplitude Odor concentration Taste type (sugary, salt, Modality (touch, temp, information Spatial location Frequency Odor identity umami, bitter, sour) pain) (receptive field) Location Intensity Intensity Timing Sensory cell: Photoreceptor Inner hair cell Olfactory neuron (ON), Taste cells arranged in Dorsal root ganglion (DRG) AP or graded - Graded potential - Graded potential cilia project into nasal taste bud cell, nerve endings in - Depolarized / releasing - Do not regenerate mucosa - AP periphery response? NT in the dark - AP - Lots of turnover - AP - Lots of turnover Signal Rhodopsin: GPCR bound Trp mechanoreceptor, Many GPCRs, each - Sweet, umami: GPCR - Trp mechanoreceptors receptor to 11-cis-retinal coupled to extracellular encoded by unique dimer - MEC mechanosensitive ion tip link and cytoskeleton gene (~1000 in - Bitter: GPCR monomer, channels mammals), each ON many - Degenerins expresses only 1 - Salt: Amiloride-sensitive receptor Na channels (degenerins) - Sour: Trp channel + GPCR Signal Photon converts retinal Trp channel opens -> K+, GPCR -> Golf -> - Bitter, sweet, umami: Activated transduction to all-trans-retinal -> Ca influx -> depolarization adenylate cyclase -> GPCR -> PLC, no details mechanoreceptors allow ion Rhodopsin activated -> of hair cell, NT release via cAMP -> open cAMP - Salt: Pass directly flux -> nerve depolarization pathway in G-protein transducin -> dense body gated Na, Ca channel -> through Na channel sensory cell phosphodiesterase -> depolarized cell fires AP cGMP levels decrease -> cGMP gated Na, Ca channel closes -> cell hyperpolarizes 1 Coding - “Off” retinal ganglion 1. Place code: where hair - 1 receptor/ON, Labelled line model: Taste Slowly adapting receptors -> cells firing in dark, “On” cell is on basilar though 1 receptor can cells are tuned to single signal pressure and shape of retinal ganglion cells membrane determines bind multiple odors taste modality, as are object firing in light frequency - Increasing odor secondary afferent Rapidly adapting receptors - - Center surround 2. Frequency code: concentration activates neurons > signal motion of objects antagonism mediated by auditory neuron fires at greater number of ONs on skin inhibitory horizontal and sound wave frequency - All ONS expressing 1 amacrine cells (true up to 1000 Hz) receptor project to - Mangocellular retinal 3. Stellate chopper cells same glomerulus in ganglion cells (RGCs) fire at frequency of sound olfactory bulb encode “where” info, wave, bushy cells respond Parvocellular RGCs to start/end of stimulus: encode “what” info sound localization Mechanisms 1. Ca influx relieves 1. Ca influx activates 1. Activated GPCR is Not discussed Slow or fast depending on of inhibition of guanylyl myosin motors, physically phosphorylated and stimulus type cyclase -> cGMP levels move and close Trp desensitized adaptation increase -> channel 2. Ca influx -> photoreceptor 2. Outer hair cells vibrate calmodulin -> close depolarizes and dampen basilar cAMP gated channel 2. Pupil dilates in low membrane light, constricts in high 3. Middle ear muscles light contract and reduce stapes vibration Mechanisms 1 photon -> 1 rhodopsin Tympanic membrane is Not discussed Not discussed Not discussed of -> activates 100 35X larger than oval transducins -> each window amplification activates 1 phosphodiesterase -> cleaves 1,000 cGMP: 105 cGMP cleaved / photon Information Photoreceptor -> Bipolar Hair cell -> Cochlear Olfactory neuron -> Taste cell -> Bipolar - Touch/Proprioception: pathway in cell -> Ganglion cell -> nucleus (medulla) -> Olfactory bulb neuron -> Gustatory DRG -> Spinal cord dorsal Thalamus LGN -> Cortex Superior olivary nucleus glomeruli -> Pyriform nucleus (medulla) -> column -> synapse in dorsal CNS layer IV, Superior (pons) -> Inferior cortex, hippocampus, Thalamus VPN -> column nucleus (medulla) -> colliculus (Tectum), colliculus -> Thalamus amygdala Gustatory cortex Cross midline -> Thalamus Superchiasmatic nucleus MGN -> primary auditory ** Only sensory system (temporal lobe) VPN -> Post-central gyrus (Hypothalamus) cortex (temporal lobe) that doesn’t relay (parietal) 2 Dorsal flow (to region through thalamus - Nocioception: DRG neuron MT): “where” before reaching cortex -> synapse in spinal cord Ventral stream (to dorsal horn -> Cross midline region IT): “what” -> Spinothalamic tract -> Thalamus VPN -> cortex Cortex Ocular dominance Cortical neurons grouped Not discussed Not discussed Somatosensory map on mapping columns (each eye by sound frequency cortex; inputs grouped segregated), orientation depending on spatial columns, “blobs” location on body segregated by color Important Myopia, astigmatism, Conductive deafness, Not discussed Not discussed Referred pain, phantom pathologies rod disease, macular sensorineural deafness, limb, hyperanalgesia, degeneration, color central deafness chronic neuropathic pain blindness, optic neuritis, glaucoma, diabetic retinopathy, cataracts, amblyopia, agnosia 3 MIT OpenCourseWare http://ocw.mit.edu 7.29J / 9.09J Cellular Neurobiology Spring 2012 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms..
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