Concepts CNS part 2 & Intro to Sensory Systems

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:


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


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


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


BrainFunction:LearningandMemory• Learning– Theacquisitionofknowledge

• Twobroadtypes• Associativelearning – 2stimuli areassociatedtogether

• Nonassociative learning• Repeatedexposuretosinglestimulus

• Habituation andsensitization


BrainFunction:Language• Left cerebral hemisphere

• Integration ofspokenlanguage involves tworegions

• Damage toWernicke’s area causesreceptiveaphasia

• Unable tounderstandsensoryinput• Damage toBroca’s area causesexpressiveaphasia

• Unable tounderstandcomplexsentences


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

area© 2016 Pearson Education, Inc.

Figure9-17

PET Scans of Functional Brain Areas

BrainFunction:Personality

• Combinationofexperienceandinheritance• Schizophrenia

• Bothgeneticandenvironmentalbasis


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


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


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

©2016PearsonEducation,Inc. © 2016 Pearson Education, Inc.


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


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.


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


TemperatureReceptors

• Free nerve endings• Terminate insubcutaneouslayers• Coldreceptors

• Lowerthanbodytemperature• Warmreceptors

• Abovebodytemperaturetoabout45°C• Painreceptorsactivatedabove45°C

• Thermoreceptors usecation channelscalledtransient receptor potential (TRP)channels

•


Nociceptors

• Respondtostrongnoxiousstimulusthatmaydamage tissue

• Free nerve endings• Primary sensoryfibers• Aδ fibers• Cfibers


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)


Nociceptors Pathways

• Modulatedbylocal chemicals• SubstancePissecretedbyprimarysensoryneurons• Mediateinflammatoryresponse• Inflammatorypain

• Ischemia islackofadequate bloodflow• Referred pain• Chronicpain isapathological (neuropathic)pain


Figure10.11aReferredpain


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


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.


PainModulation

• Analgesic drugs• Aspirin

• Inhibitsprostaglandins,decreasesinflammation,andslowstransmissionofpaintositeofinjury

• Opioids• Blockpainperceptionbydecreasingprimarysensoryneuronneurotransmitterreleaseandbypostsynapticinhibitionofsecondarysensoryneurons

• Endorphins,enkephalins,dynorphins

©2016PearsonEducation,Inc. © 2016 Pearson Education, Inc.

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Concepts CNS part 2 & Intro to Sensory Systems