concepts cns part 2 & intro to sensory systems part 2 & intro to sensory systems ... •...
TRANSCRIPT
Biol 219Lecture15Fall2016 Dr Scott
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CNSpart2&IntrotoSensorySystems
BrainFunction– ImportantConcepts• Functionalareasofthecerebralcortex
• Sensory, Motor,Association
• Cerebrallateralization– eachhemispherehasfunctionsnotsharedbytheother
• TheSpinalCordandBrainIntegrateSensoryInformation
• PrimarySomaticSensoryCortex– Inputfromsomaticsenses
• TheSpecialSenseslocalizetoothercorticalregions• PrimaryMotorCortex– Voluntarymovement(Output)
Functional Areas of the Cerebral Cortex BrainFunction– ImportantConcepts• AssociationAreas- SensoryInformationisProcessedintoPerceptionØThebrain’s interpretation ofthesensorystimuli
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BrainFunction– ImportantConcepts
• TheBehavioralStateSystem• Controlssensoryandcognitiveprocessing
• Levelsofconsciousness(awarenessofselfandtheenvironment)
• Sleep-wake cycles
• Diffusemodulatory systems
• Reticularformationinthebrainstem,HT,&limbicsystem
DiffuseModulatorySystems(4)
• Regulatebrainfunctionbyinfluencing• Attention• Motivation• Wakefulness• Memory• Motorcontrol
• Mood• Metabolichomeostasis
Figure 9.16a Diffuse modulatory systemsNoradrenergic (Norepinephrine)
Functions: Attention, arousal, s leep-wake cycles, learning,memory, anxiety, pain, and mood
Locus coeruleus of the ponsNeurons Originate:
ThalamusNeurons Terminate:
Hypothalamus CerebellumLocus coeruleus
Cerebral cortex, thalamus, hypothalamus,olfactory bulb, cerebellum, midbrain, spinal cord
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Figure 9.16b Diffuse modulatory systems
Serotonergic (Serotonin)
Functions:
To basalnuclei
Neurons Originate:
1. Lower nuclei: Pain, locomotion2. Upper nuclei: Sleep-wake cycle; mood and
emotional behaviors, such as aggressionand depression
Raphe nuclei a long brain stem midline
Raphenuclei
Neurons Terminate:2. Upper nuclei project to most of brain1. Lower nuclei project to spinal cord
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Figure 9.16c Diffuse modulatory systemsDopaminergic (Dopamine)
Functions:
Prefrontalcortex
1. Motor control2. “ Reward” centers linked to
addictive behaviors
1. Substantia nigra in midbrain2. Ventral tegmentum in midbrain
1. Cortex2. Cortex and parts of limbic system
To basalnuclei
Substantianigra
Ventraltegmental area
Neurons Originate:
Neurons Terminate:
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Figure 9.16d Diffuse modulatory systemsCholinergic (Acetylcholine)
Functions: Sleep-wake cycles, arousal, learning, memory,sensory information passing through thalamus
Base of cerebrum; pons and midbrain
Cerebrum, hippocampus, thalamus
Cingulategyrus
Neurons Originate:
Neurons Terminate:
Fornix
Pontinenuclei
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BrainFunction:Sleep
• Fourstageswithtwomajorphases• Slow-wave sleep
• Adjustsbodywithoutconsciouscommands
• Rapideyemovement (REM)sleep
• Brainactivity inhibitsmotorneuronstoskeletal muscle,paralyzing them
• Dreaming takesplace
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BrainFunction:Sleep
Sleepdisorders• Insomnia:inabilitytosleep• Sleepapnea:stoppingnormalbreathingduringsleep
• Somnambulism:sleepwalking
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• TotheN.F.L., 40WinksIsasVital as the40-YardDash
Inthenever-ending search foranedge, teams haveopened theireyes tosleepasapriority, backedupbyscience that increasinglypointstoitsimportance forphysicalandmentalhealth.
BrainFunction:
• Circadianrhythms
• Biologicalcycleofrestandactivity
• NeuronsarelocatedinSuprachiasmaticnucleus(SCN)ofthehypothalamus
• SCNhasmelatoninreceptors- linkedtocircadianrhythmsdisruptedbyshiftworkandjetlag
BrainFunction:Motivation
• Definedasinternal signalsthat shapevoluntarybehaviors
• Somestatesknownasdrives
• Workwithautonomicandendocrine responses
• Motivatedbehaviors stopwhenapersonhasreached acertain level ofsatiety
• Pleasure andaddictivebehaviors: linktodopamine
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Figure 9.18 Emotions affect physiology
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BrainFunction:Moods• Similar toemotionsbutlonger-lasting• Mooddisorders
• Fourthleading causeofillnessworldwide today• Depression
• Sleep andappetite disturbances• Alterations ofmoodandlibido• Mayaffectfunctionat schoolorworkorinpersonal relationships
• Antidepressant drugsalter synaptictransmission
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BrainFunction:LearningandMemory• Learning– Theacquisitionofknowledge
• Twobroadtypes• Associativelearning – 2stimuli areassociatedtogether
• Nonassociative learning• Repeatedexposuretosinglestimulus
• Habituation andsensitization
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BrainFunction:Language• Left cerebral hemisphere
• Integration ofspokenlanguage involves tworegions
• Damage toWernicke’s area causesreceptiveaphasia
• Unable tounderstandsensoryinput• Damage toBroca’s area causesexpressiveaphasia
• Unable tounderstandcomplexsentences
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Speaking a Written Word
Motorcortex
Broca’sarea
Wernicke’sarea
Readwords
Visualcortex
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Speaking a Heard Word
Motorcortex
Broca’sarea
Hearwords Auditory
cortexWernicke’s
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Figure9-17
PET Scans of Functional Brain Areas
BrainFunction:Personality
• Combinationofexperienceandinheritance• Schizophrenia
• Bothgeneticandenvironmentalbasis
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https://www.youtube.com/watch?v=yH97lImrr0Q
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SensoryPhysiology– ImportantConcepts• TheSomatic Senses
• Touch
• Temperature
• Pain
• Itch
• Proprioception
• TheSpecial Senses• Vision,Hearing,Taste,Smell,Equilibrium
SensoryPhysiology
• Generalpropertiesofsensorysystems• Somaticsenses• Chemoreception:smellandtaste• Theear:hearing• Theear:equilibrium• Theeyeandvision
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Peripheral Nervous System
Central Nervous System
Afferent (Sensory)
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SensoryPhysiology– ImportantConcepts• SomatosensoryPathways
• Chainofneurons fromthe receptororgan tothecerebral cortex responsible fortheperception ofthesenses
Somatic Sensory Pathways to the Cerebral Cortex
SensoryPathways
• Stimulusasphysicalenergy→ sensoryreceptor
• Receptoractsasatransducer
• Intracellular signal→ usuallychange inmembranepotential
• Stimulus→ threshold→ actionpotential toCNS
• Integration inCNS→ cerebral cortexoractedonsubconsciously
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ReceptorstoParticularFormsofEnergy• Naked (“free”)nerves
• Complexneural receptorsencased inconnectivetissuecapsules
• Smell receptorsareneurons
• Non-neural receptors forfourspecial senses
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ReceptorstoParticularFormsofEnergy• Chemoreceptors respondtochemical ligands:taste, smell
• Mechanoreceptors respondtomechanical energypressureandsound:hearing
• Thermoreceptors respondtotemperature• Photoreceptors forvisionrespondtolight
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Simple receptors are neuronswith free nerve endings. Theymay have myelinatedorunmyelinated axons.
Complex neural receptors have nerveendings enclosed in connective tissue capsules.This illustration shows a Paciniancorpuscle,which senses touch.
Most special senses receptors are cells that release neurotransmitter onto sensory neurons, initiating an action potential. The cell illustrated is a hair cell, found in the ear.
Stimulus Stimulus Stimulus
Free nerve endings
Unmyelinatedaxon
Cell body
Enclosed nerveendingLayers of connective tissue
Myelinated axon
Cell body
Specializ ed receptorcell (hair cell)
Synaptic vesicles
Synapse
Myelinated axon
Cell body ofsensory neuron
Sensory Receptors and Sensory Neurons
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SensoryTransduction• Conversionofaphysicalstimulusintoanelectricalsignal
• Ionchannelsorsecondmessengers initiatemembrane potentialchange
• Adequate stimulus:formofenergy towhichareceptor ismostresponsive
• Threshold:minimum stimulus
• Receptorpotential: change in sensoryreceptormembrane potential
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Sensory Transduction
Receptive Field of a Sensory Neuron
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Two-Point Discrimination Test Sensory Pathways
IntegrationbyCNS
• Sensory information
• Spinal cordtobrainbyascendingpathways
• Directly tobrainstemviacranialnerves
• Visceral reflexes integrated inbrainstemor spinalcordusuallydonotreachconsciousperception.
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IntegrationbyCNS
• Perceptual threshold: levelofstimulusnecessary tobeaware ofparticular sensation
• Habituation:decreased perception throughinhibitorymodulation
• Fallsbelowperceptualthreshold
• Eachmajordivisionofthebrainprocessesoneormore typesofsensoryinformation
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1. Stimulus modality is encoded by specific neural pathways to the cerebral cortex.
2. Representation of stimulus location in the somatosensorycortex.
Perception of Sound Location Lateral Inhibition- enhances contrast between adjacent receptive fields- sharpens perception of stimulus location
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3. Stimulus intensity is encoded by thenumber of receptors activated, and...
Stimulus intensity is encoded by the frequencyof action potentials in sensory neurons
Receptor Adaptation
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SomaticSenses:Modalities
• Touch• Proprioception• Temperature• Nociception
• Pain• Itch
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TemperatureReceptors
• Free nerve endings• Terminate insubcutaneouslayers• Coldreceptors
• Lowerthanbodytemperature• Warmreceptors
• Abovebodytemperaturetoabout45°C• Painreceptorsactivatedabove45°C
• Thermoreceptors usecation channelscalledtransient receptor potential (TRP)channels
•
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Nociceptors
• Respondtostrongnoxiousstimulusthatmaydamage tissue
• Free nerve endings• Primary sensoryfibers• Aδ fibers• Cfibers
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Nociceptors
• Pain• Subjectiveperception• Fastpain
• Sharpandlocalized—byAδ fibers• Slowpain
• Dullerandmorediffuse—byCfibers
• Itch• HistamineactivatesCfibers,causingitch• Fromskinnociceptors
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Nociceptors Pathways
• Reflexive protective response• Integratedinspinalcord• Withdrawalreflex
• Ascendingpathway tocerebral cortex• Becomes conscious sensation(painoritch)
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Nociceptors Pathways
• Modulatedbylocal chemicals• SubstancePissecretedbyprimarysensoryneurons• Mediateinflammatoryresponse• Inflammatorypain
• Ischemia islackofadequate bloodflow• Referred pain• Chronicpain isapathological (neuropathic)pain
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Figure10.11aReferredpain
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Pain in internal organs is often sensed on the surface of the body, a sensation known as referred pain.
Heart
Liver andgallbladder
Stomach
Appendix
Colon
Smallintestine Ureters
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Figure10.11bReferredpain
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One theory of referred pain says that nociceptors from severallocations converge on a single ascending tract in the spinal cord. Pain signals from the skin are more common than pain from internal organs, and the brain associates activation of the pathway with pain in the skin. Based on H.L. Fields, Pain (McGraw Hill, 1987).
Skin(usual stimulus)
Kidney(uncommon stimulus)
Secondarysensory neuron
Primary sensory neurons
Ascending sensorypath to somatosensory
cortex of brain
PainModulation
• Gatecontroltheory: Aβfibers synapseoninhibitoryinterneuronsandincrease inhibition
• IntegratedresponsefromAβandCfibersdecreasestheperceptionof pain.
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PainModulation
• Analgesic drugs• Aspirin
• Inhibitsprostaglandins,decreasesinflammation,andslowstransmissionofpaintositeofinjury
• Opioids• Blockpainperceptionbydecreasingprimarysensoryneuronneurotransmitterreleaseandbypostsynapticinhibitionofsecondarysensoryneurons
• Endorphins,enkephalins,dynorphins
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