11 Sensory Phys · 2018-03-12 · SENSORY PHYSIOLOGY Physiology Unit 2. Sensory Pathways in the Brain. Sensory System •Sensory information –Conscious sensations –Unconscious

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