Chapter 10SensorySensory PathwaysSensory ReceptorsSensory TransductionIntegration by CNSPowerPoint PresentationProperties of Stimulus: Intensity and DurationSlide 9The Olfactory SystemSlide 11Slide 12TasteSlide 14Slide 15The Ear: HearingSlide 17Slide 18Auditory PathwaysHearing LossThe Vestibular ApparatusSlide 22Slide 23The Eye and VisionSlide 25Slide 26VisionThe PupilThe LensSlide 30Slide 31MyopiaHyperopiaPhototransductionSlide 35Slide 36Slide 37Slide 38PhotoreceptorsFigure 1.30Chapter 10•General properties of sensory systems•Somatic senses•Chemoreception: smell and taste•The ear: hearing•The ear: equilibrium•The eye and vision© 2013 Pearson Education, Inc.SensorySensory Pathways•Stimulus as physical energy  sensory receptor–Receptor acts as a transducer•Intracellular signal  usually change in membrane potential•Stimulus  threshold  action potential to CNS•Integration in CNS  cerebral cortex or acted on subconsciously© 2013 Pearson Education, Inc.Sensory ReceptorsSensory Transduction•Stimulus energy converted into information processed by CNS–Ion channels or second messengers initiate membrane potential change•Adequate stimulus: Form of energy to which a receptor is most responsive •Threshold: Minimum stimulus•Receptor potential: Change in sensory receptor membrane potential© 2013 Pearson Education, Inc.Integration by CNS•Sensory information–Spinal cord to brain by ascending pathways–Directly to brain stem via cranial nerves•Visceral reflexes integrated in brain stem or spinal cord usually do not reach conscious perception•Perceptual threshold: level of stimulus necessary to be aware of particular sensation•Each major division of the brain processes one or more types of sensory information© 2013 Pearson Education, Inc.SENSORY PATHWAYS IN THE BRAINMost pathways pass through the thalamus on their way to the cerebral cortex.Gustatory cortexOlfactory cortexOlfactory bulbEyeNoseTongueThalamusBrainstemSomaticsensesEquilibriumCerebellumSoundVisual cortexAuditory cortexPrimary somaticsensory cortexOlfactory pathways fromthe nose project throughthe olfactory bulb to theolfactory cortex.Most sensory pathways projectto the thalamus. The thalamusmodifies and relays informationto cortical centers.Equilibrium pathways projectprimarily to the cerebellum.FIGURE QUESTIONWhich sensory pathways showndo not synapse in the thalamus?Properties of Stimulus: Intensity and Duration•Intensity–Coded by number of receptors activated and frequency of action potentials•Duration–Coded by duration of action potentials–Some receptors can adapt, or cease to respond•Tonic receptors versus phasic receptors © 2013 Pearson Education, Inc.The Olfactory SystemOlfactory PathwaysOlfactory bulbCranial Nerve IOlfactoryneuronsin olfactoryepitheliumOlfactory tractOlfactory cortexCerebral cortexLimbicsystemThe olfactory epithelium lies high withinthe nasal cavity, and its olfactory neuronsproject to the olfactory bulb. Sensory inputat the receptors is carried through theolfactory cortex to the cerebral cortexand the limbic system.The Olfactory SystemThe olfactory neurons synapse with secondary sensory neurons in the olfactory bulb.OlfactorybulbBoneOlfactoryepitheliumOlfactory sensoryneuronsSecondarysensory neuronsFIGURE QUESTIONMultiple primary neurons in theepithelium synapse on onesecondary neuron in the olfactorybulb. This pattern is an exampleof what principle?The Olfactory SystemOlfactory neurons in the olfactory epithelium live only abouttwo months. They are replaced by new neurons whose axonsmust find their way to the olfactory bulb.Olfactory neuronaxons (cranial nerve I)carry information toolfactory bulb.Lamina propriaSupporting cellBasal cell layer includesstem cells that replaceolfactory neurons.Developingolfactory neuronOlfactorysensory neuronOlfactory cilia(dendrites) containodorant receptors.Mucous layer:Odorant molecules mustdissolve in this layer.TasteTaste transduction. Each taste cellsenses only one type of ligand.Receptor cells with G protein–coupledmembrane receptors bind either bitter,sweet, or umami ligands and releaseATP as a signal molecule.Sweet, umami,or bitter ligandGustducinGPCRSignaltransductionATPCa2Ca2Ca2Ca2HH???PrimarygustatoryneuronsPresynaptic cells sense sour taste(H) but it is not clear whether Hacts on a receptor or enters the cell.SourLigands activate the taste cell. Ca2 signal in the cytoplasmtriggers exocytosis or ATPformation.Various intracellular pathwaysare activated.Neurotransmitter or ATP isreleased.Primary sensory neuron firesand action potentials aresent to the brain.The Ear: Hearing•Perception of energy carried by sound waves•Frequency is translated into pitch•Loudness is an interpretation of intensity, a function of wave amplitude© 2013 Pearson Education, Inc.SOUND TRANSMISSION THROUGH THE EARSound wavesstrike thetympanicmembraneand becomevibrations.The soundwave energy istransferred tothe three bonesof the middleear, whichvibrate.The stapes isattached to themembrane of the ovalwindow. Vibrations ofthe oval windowcreate fluid waveswithin the cochlea.The fluid waves push onthe flexible membranesof the cochlear duct. Haircells bend and ionchannels open, creating anelectrical signal that altersneurotransmitter release.Neurotransmitterrelease onto sensoryneurons creates actionpotentials that travelthrough the cochlearnerve to the brain.Energy from the wavestransfers across thecochlear duct into thetympanic duct and isdissipated back intothe middle ear at theround window.Ear canalMalleusIncusStapesOvalwindowMovementof soundwavesTympanicmembraneRoundwindowCochlear nerveVestibular duct(perilymph)Cochlear duct(endolymph)Tympanic duct(perilymph)SIGNAL TRANSDUCTION IN HAIR CELLSThe stereocilia of hair cells have “trap doors” that close off ion channels. Theseopenings are controlled by protein-bridge tip links connecting adjacent cilia.At rest: About 10% of the ionchannels are open, and a tonic signalis sent by the sensory neuron.Excitation: When the hair cells bendin one direction, the cell depolarizes,which increases action potentialfrequency in the associated sensoryneuron.Inhibition: If the hair cells bend in theopposite direction, ion channels close,the cell hyperpolarizes, and sensoryneuron signaling decreases.Tip linkStereociliumHair cellSome channels openPrimarysensoryneuronMore channelsopen.Cation entrydepolarizescell.Channels closed.Less cation