SENSORYPHYSIOLOGY
PhysiologyUnit2
SensoryPathwaysintheBrain
SensorySystem
• Sensoryinformation– Conscioussensations– Unconscioussensations
• Sensoryprocessing– Transferringstimulusenergyintoagradedpotential(receptorpotential)
– Thentoanactionpotentialinanafferentneuron• Patternofactionpotentialsisthecodethatprovidesinformationonthestimulus
GeneralClassesofReceptors
• Mechanoreceptors• Thermoreceptors• Photoreceptors• Chemoreceptors• Nociceptors
SensoryReceptors• Specializedendingsof
sensoryneurons• Separatecellsthatsignal
theafferentneuronsbyreleasingchemicalmessengers
• Theenergyorchemicalthatactivatesasensoryreceptorisastimulus
• Theprocessbywhichastimulusistransformedintoanelectricalresponseissensorytransduction
ReceptorPotential
• Sensorytransductioninvolvestheopening/closingofionchannels
GradedPotentialtoActionPotential
• Theinitialionmovementgenerateslocalcurrentthatflowsashortdistancealongtheaxontoaregionwherethemembranehasvoltage-gatedionchannelsananAPcanbegenerated
• UsuallythefirstNodeofRanvier
SensoryModality
• Modalities– Temperature,taste,sound,touch
• Submodalitiesofsensation– Submodalityoftemperature:hot/cold– Submodalitiesoftaste:sweet,bitter,salty,sour,umame
– Submodalityofsound:pitch,volume
PrimarySensoryCoding
• ConvertingstimulusenergythatconveysrelevantsensoryinformationtotheCNSiscoding– Typeofenergyitrepresents(modality)
– Intensity– Locationofthebodyaffected
Sensory Unit
StimulusIntensity
StimulusDuration• Rapidadaptation
– Phasicreceptors– Signalchange– Rapidfadingofsensation– “on” and“off” response
• Slowadaptation– Tonicreceptors– Signalslowchangesor
prolongedevents– Joint,musclereceptorsfor
maintainingposture
SomaticSenses
• 4SomatosensoryModalities1. Touch2. Proprioception3. Temperature4. Nociception
– Pain– Itch
SomaticSensation• Sensationsfrom
– Skin– Muscles– Bones– Tendons– Joints
• Sensationsof– Touch– Pressure– Bodyposition– Temperature– Pain
SensoryPathways• ASensoryPathway
– Abundleofparallel neuronsthatruntogether– Receptoractivation– 1storder(primary)sensoryneuron– 2nd order(secondary)sensoryneuron
– aninterneuron– decussation
– 3rd order(tertiary)sensoryneuron– Alsocalledascendingpathways
– Non-specific– Specific
– Manysensorypathwaysalsosendinformationtothecerebellumtocoordinatebalanceandmovement
– Mostsensorypathwaysconveyinformationfromasinglemodality
SpecificAscendingPathways• AscendingPathways
1. ThroughtheBrainstem(RAS)2. Thalamus3. Finalneuronsinthepathwayterminateinthe
specificsensoryareaofthecortexandthecerebellum
• Exception:olfactoryneuronsbranchtotheolfactorycortexandamygdala/hippocampus(limbicsystem)ratherthanthethalamus• Odorsarecloselyassociatedwithmemoriesandemotions
SomatosensorySystemPathwaysAnterolateralPathway
• 1st neurontravelsintothespinalcord
• 2nd neurondecusatesinthespinalcordanduptothethalamus
• 3rd neurontravelstothesomatosensorycortex
• Processes• Nociception• Temperature• Coursetouch
Decusationinthespinalcord
SomatosensorySystemPathwaysDorsalColumnPathway
• 1st neuronpassesintothespinalcordanduptothebrainstemwhereitdecusates
• 2nd neurontravelstothethalamus
• 3rd neurontravelstothesomatosensorycortex
• Processes• Finetouch• Vibration• Proprioception
Decusationinthebrainstem
DistributionofPeripheralStimuli
SpecialSense:Vision
• Opticalcomponent– Focusesvisualimageonthereceptorcells
• Neuralcomponent– Transformsthevisualimagetoapatternofgradedandactionpotentials
Light
• Thereceptorsoftheeyeareonlysensitivetoasmallportionoftheelectromagneticspectrum
• Thevisiblespectrumisbetween400-750nm
• Differentwavelengthsoflightareperceivedasdifferentcolors
ColorVision
TheOpticsofVision
• Refractinglightishowoureyesfocusonobjects
• Thecorneaandthelensrefractlighttofocusitintheretina
• Adjustmentsfordistanceismadebychangestheshapeofthelens.Thisisaccommodation
Accommodation
PhotoreceptorCells• Outersegmentmadeof
stackedlayersofmembrane(discs).
• Thediscsholdthephotopigments whichabsorblight
• Photopigmentsaremembraneboundproteinscalledopsins whichsurroundandbindamoleculecalledretinal• Retinolisaderivativeof
vitaminA
PhotoreceptorCells
• Thereare4uniquephotopigments intheretina(calledphotopsins)• Rodshavethephotopigmentrhodopsin
• Theothersarefoundinthe3typescones
Phototransduction
NeuralPathwayofVision
• Pathway:– Photoreceptorsoftheretina
– OpticNerve(C.N.II)– Opticchiasm
• SCN
– Optictract– Thalamus– Visualcortex
Suprachiasmaticnucleus(SCN)controlscircadianrhythms
SpecialSense- Hearing
SoundTransmission
OrganofCorti
Sensory Hair Cells
NeuralPathwayforHearing
• Pathway:– Sensoryhaircells– Cochlearbranchofvestibulocochlearnerve(C.N.VIII,AuditoryNerve)
– Brainstem– Midbrain– Thalamus– Auditorycortex
VestibularSystem
• Vestibularapparatus– Semicircularcanals
–Utricle– Saccule
SemicircularCanalsRotationalMovement
UtricleandSacule• Themaculaprovidesinfoonchangesinheadpositionrelativeto:– Forceofgravity– Linearacceleration
• Vestibularinformationisusedfor:– Controleyemovements– Reflexestomaintainposture
– Consciousawarenessofourselvesin“space”
Gustation
Olfaction