nervous sytem v3

7/29/2019 Nervous Sytem V3

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THE NERVOUS SYSTEM


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TheNervousSystem

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FunctionoftheNervousSystem

Tocoordinatetheactionsofyourbody

Toensureeffectivebehavior To maintain the internal environment within safelimits(homeostasis)

Messages are relayed throughout the body via

electrochemical messages from the brain orthrough chemical messengers hormones(hormones require more time than nervoustransmissionbutarelonglasting)

TherearemorenervecellsinthebodythantherearevisiblestarsintheMilkyWay!

1cm3ofbraintissuehousesseveralmillionneuronswitheachconnectingwithseveralthousandothers

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NervousTissue

Thenervoussystemisdividedintoacentralnervous system (CNS), consisting of the

brain and spinal cord, and a peripheral

nervous system (PNS), consisting ofnerves carrying sensory and motor

informationbetweentheCNSandmuscles

andglands.Both systems have two types of cells:

neurons that transmit impulses and

neuroglialcellsthatsupportneurons.17-4


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Organizationofthenervous

system

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NeuronStructure

Neurons are composed of dendrites thatreceivesignals,acellbodywithanucleus,and an axon that conducts a nerveimpulseaway.

Sensory neurons take information fromsensoryreceptorstotheCNS.

Interneurons occur within the CNS and

integrateinput(nonmyelinated).Motor neurons take information from theCNStomusclesorglands.

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Typesofneurons

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dendrites receive information (either from

receptor cells or other nerve cells),conducting towards the cell body (~200

dendrites/cellbody)

cell body location of the nucleus, highmetabolicrate(socontainsmitochondria)

axonmay be 1m long, very thin, conducts

the impulse towards other neurons oreffectors,startsataxonhillock,thesmaller

the neuronal diameter, the faster the

neuronaltransmission17-9


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nodes of Ranvier the unmyelinated

sections of a myelinated neuron,

impulses jump between the nodesofRanvier

neurilemmaathinlayerencompassing

neurons in the peripheral nervoussystem,promotingtheirregeneration

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Schwanncellresponsibleforthemyelin

synthesis,typeofglialcell(supportingand

nourishingcellfoundinthenervous

system)

AxonBulbeitheratasynapticbulborend

platetomuscle,containsneurotransmitter

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MyelinSheath

Myelination covers long axons with aprotective myelin sheath (made byneuroglialcellscalledSchwanncells).

Thesheathcontainslipidmyelinwhichgivesnerve fibers their white, glisteningappearance.

The sheath is interrupted by gaps callednodesofRanvier.

Multiplesclerosisisadiseaseofthemyelinsheath.

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http://www.siumed.edu/~dking2/ssb/neuron.htmhttp://www.siumed.edu/~dking2/ssb/neuron.htmhttp://www.siumed.edu/~dking2/ssb/neuron.htm


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Myelinsheath

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FYI

Nerves are generally comprised of many

neuronstogether(likefibreopticcable)

Myelinatedneurons in thebrainare termed

whitematter(themyelinmakesthemlook

white)

White matter may regenerate after injury,

whereasgreymatter(unprotected)willnot

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TheNerveImpulse

Thenervoussystemusesthenerveimpulse

toconveyinformation.

The nature of a nerve impulse has been

studied by using excised axons and a

voltmetercalledanoscilloscope.

Voltage (in millivolts, mV) measures the

electricalpotentialdifferencebetween theinsideandoutsideoftheaxon.

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MembranePolarization(RestingPotential)

When an axon is not conducting a nerve

impulse, the inside ofan axon is negative (-

70mV)comparedtotheoutside(+40mV);this

istherestingpotential.

Toestablishthe70mVpotentialinthecell:

Na+isactivelypumpedoutofthecell

K+isactivelypumpedintothecell

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Sodium pump
http://d/Bio30/Nervous%20System/Rest%20Potent%20Anim.movhttp://d/Bio30/Nervous%20System/Rest%20Potent%20Anim.mov


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MembranePolarization(RestingPotential)

Na+ and K+ diffuse down theconcentration gradient, but K+ diffusesfasterdue toan increased numberof ion

channels(gates)opentoK+ions Sincethereisanetlossofpositiveionstothe outside of the cell, -70 mV isestablishedinsidetheneuron

There are also large negative proteinsinside the neuron that contribute to thenegativecharge

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http://d/Bio30/Nervous%20System/Rest%20Potent%20Anim.movhttp://d/Bio30/Nervous%20System/Rest%20Potent%20Anim.mov


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Restingpotential

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MembraneDepolarization

When the nerve cell is excited, themembrane DEPOLARIZES (ActionPotential)

Themembranespolaritychanges: Na+ channels open, Na+ rushes in, K+gatesclose

Thepositiveionsflowingincausesachargereversalto+40mVinsidetheneuron

(gatedchannelproteins)

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http://d/Bio30/Nervous%20System/Actn%20Potent%20Anim.movhttp://outreach.mcb.harvard.edu/animations/actionpotential.swfhttp://outreach.mcb.harvard.edu/animations/actionpotential.swfhttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/anim0013.swf::Voltage%20Gated%20Channels%20and%20the%20Action%20Potentialhttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/anim0013.swf::Voltage%20Gated%20Channels%20and%20the%20Action%20Potentialhttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/anim0013.swf::Voltage%20Gated%20Channels%20and%20the%20Action%20Potentialhttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/anim0013.swf::Voltage%20Gated%20Channels%20and%20the%20Action%20Potentialhttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/anim0013.swf::Voltage%20Gated%20Channels%20and%20the%20Action%20Potentialhttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/anim0013.swf::Voltage%20Gated%20Channels%20and%20the%20Action%20Potentialhttp://outreach.mcb.harvard.edu/animations/actionpotential.swfhttp://outreach.mcb.harvard.edu/animations/actionpotential.swfhttp://outreach.mcb.harvard.edu/animations/actionpotential.swfhttp://d/Bio30/Nervous%20System/Actn%20Potent%20Anim.mov


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Actionpotential

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MembraneRepolarization

Oncethechargebecomespositive,theNa+

gates close, K+ gates open, eventually

restoringthechargeinsidetheneuronto70mV(buttheNa+excessisinsideand

K+excessisoutside!)

The Na/K Pump restores the ion

concentrationsinsideandoutsidethecell

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http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/bio_a.swf::Sodium-Potassium%20Exchangehttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/bio_a.swf::Sodium-Potassium%20Exchangehttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/bio_a.swf::Sodium-Potassium%20Exchangehttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/bio_a.swf::Sodium-Potassium%20Exchangehttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/bio_a.swf::Sodium-Potassium%20Exchangehttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/bio_a.swf::Sodium-Potassium%20Exchange


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MembraneRepolarization

During the repolarization, the nerve

cannot be reactivated this is called

therefractoryperiod(1to10ms)andisarecoverytimefortheneuron

The pump requires ATP in order to

operate

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TheNa/KPump

To be ready for another action potential,themembranere-establishestheproper

concentration gradient for sodium andpotassium

ThreesodiumionsareactivelytransportedacrossthemembraneandtotheECM

Two potassium ions are then carriedacrosstothecytoplasm

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http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/bio_a.swf::Sodium-Potassium%20Exchangehttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/bio_a.swf::Sodium-Potassium%20Exchange


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MovementoftheActionPotential

Theactionintheneuronadjacenttoanareaof restingmembrane causes that area to

depolarize, moving the action potential

along (due to attraction of oppositecharges)

Since the area from which the action

potential came is still in recovery, theaction potential will only move in one

direction

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PropagationofanActionPotential

The action potential travels the length of anaxon, with each portion of the axonundergoing depolarization then

repolarization.A refractory period ensures that the actionpotentialwillnotmovebackwards.

Inmyelinated fibers, theaction potential onlyoccursatthenodesofRanvier.

This jumping from node-to-node is calledsaltatoryconduction.

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Fig.48-13
http://highered.mcgraw-hill.com/olc/dl/120107/bio_d.swfhttp://highered.mcgraw-hill.com/olc/dl/120107/bio_d.swfhttp://www.siumed.edu/~dking2/ssb/saltcon.htmhttp://www.siumed.edu/~dking2/ssb/saltcon.htmhttp://www.siumed.edu/~dking2/ssb/saltcon.htmhttp://www.siumed.edu/~dking2/ssb/saltcon.htmhttp://highered.mcgraw-hill.com/olc/dl/120107/bio_d.swfhttp://highered.mcgraw-hill.com/olc/dl/120107/bio_d.swfhttp://highered.mcgraw-hill.com/olc/dl/120107/bio_d.swfhttp://highered.mcgraw-hill.com/olc/dl/120107/bio_d.swf


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Cell body

Schwann cell

Depolarized region(node of Ranvier)

Myelinsheath

Axon


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TheAll-or-NoneResponse(ThresholdPotential)

Allneuronsprovideanall-or-noneresponse:

- in response to a stimulus, they either activate

(fire)andprovideacertainlevelofresponse,or

dontfireatallA neuron will only fire if it is stimulated with an

intensityofatleastthresholdlevel

Every action potential for a neuron is identical instrengthandduration(regardlessofhowmuch

beyondthresholdthestimulusis)

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ThresholdPotential

Allneuronsdifferintheirthresholdlevel

To inform the brain of the intensity of a

stimulus:

- the frequency of firing is increased (notspeed,whichisconstantforeachneuron)

- the number of neurons that respond to

that level of stimulus can increase(neuronsmayhavedifferentthreshold)

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TransmissionAcrossaSynapse

Thejunctionbetweenneuronsorneurons&

effectorsiscalledthesynapse.

Transmission of a nerve impulse takesplace when a neurotransmitter molecule

storedinsynapticvesiclesintheaxonbulb

isreleasedintoasynapticcleftbetweentheaxonandthereceivingneuron.

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http://ca.youtube.com/watch?v=70DyJwwFnkU&feature=relatedhttp://ca.youtube.com/watch?v=70DyJwwFnkU&feature=related


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When a nerve impulse reaches an axon

bulb,calciumchannelsopenandCa2+flowintothebulb.

This sudden rise in Ca2+ causes synaptic

vesicles to move and merge with thepresynaptic membrane, releasing theirneurotransmitter molecules into thesynapse

The binding of the neurotransmitter toreceptors in the postsynaptic membranecauseseitherexcitationorinhibition.

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Synapsestructureandfunction

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http://d/Bio30/Nervous%20System/SynapseAnim.movhttp://d/Bio30/Nervous%20System/SynapseAnim.mov


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SynapticSummation

Many synapses per single neuron is not

uncommon.

Excitatorysignalshaveadepolarizingeffect,and inhibitory signals have a

hyperpolarizingeffectonthepost-synaptic

membrane.Summation is the summing up of these

excitatoryandinhibitorysignals.

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Summation

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Summation


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NeurotransmitterMolecules

Outof 25, twowell-knownneurotransmittersareacetylcholine(ACh)andnorepinephrine(NE).

Neurotransmitters that have done their jobare removed from the cleft; the enzymeacetylcholinesterase (AChE) breaks downacetylcholine.

Neurotransmitter molecules are removedfrom the cleft by enzymatic breakdown orbyreabsorption,thuspreventingcontinuousstimulationorinhibition.

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FYI

mostsynapsesinvolvemorethanjust2neurons

(orneuron/effectors)

neurotransmitters move only by diffusion, so

synaptic transmission is MUCH slower than

axonaltransmission. insecticides interfere with enzymes that break

down neurotransmitters causing their hearts to

remaincontracted,

whereas LSD and other hallucinogens arebelieved to bind to the receptor sites for

neurotransmitters

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Lidocaine,ananestheticworksbystabilizingthe

neuronalmembranesoitcantdepolarize Endorphinsandenkephalinsarenatural

painkillersproducedintheCNS,blockingthe

paintransmitterthatusuallyattachestothe

injuredorganallowingtheperceptionofpain

opiates(heroin,codeine,morphine)blockthe

productionofthepaintransmitter.Sincethey

acttodecreasetheproductionofnaturalpainkillers,theamountofopiatetakenmustbe

increasedoratleastmaintainedtomaintainthe

effect

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Valiumandotherdepressantsarebelievedto enhance the action of inhibitorysynapses

Alcoholactstoincreasethepolarizationofthemembrane,increasingthethreshold

Since many neurons will connect to apostsynapticneuron,itisthesummationof

theeffectsofthepresynapticneuronsthatdeterminewhetherornotthepostsynapticneuronoreffectorwilldepolarize

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NeuralCircuitsincludesneuronalandsynaptictransmission

Therearetwotypesofneuralcircuits

complicated neural circuits, involving

consciousthought

reflexarcswithoutbraincoordination often unconscious, involuntary and fasterthan when thought is required (why are

theseuseful?)

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NervousControl(ingeneral)StimulusReceptorSensoryNeuronInterneuron

Brain

Interneuron

MotorNeuron

Effector

Response

ReflexArc(seediagramthereflexarc)StimulusReceptorSensoryNeuronInterneuron

(spinalcord)MotorNeuronEffectorResponse

Whentheresponseismadeatthespinalcordlevel(informationdoesnothavetogotothebraintobe

processed),theresponseisquick(andalwayscorrectgiventhecircumstances)

Reflexesprotectthebodyfrominjury

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TheCentralNervous

SystemThe central nervous system (CNS)

consistsofthespinalcordandbrain.

Both are protected by bone, wrapped inprotectivemembranescalledmeninges,

and surrounded and cushioned with

cerebrospinal fluid that is produced intheventriclesofthebrain.

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The ventricles are interconnecting cavitiesthat produceand serveasa reservoir for

cerebrospinalfluid.

The CNS receives and integrates sensoryinputandformulatesmotoroutput.

Graymatter contains cell bodies and short,

nonmyelinated fibers; white matter contains myelinated axons that run in

tracts.

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TheBrain

consumesmoreoxygenandglucosethananyotherpartofthebody

meningesouterlayers(protection)dura

mater,arachnoidandpiamater cerebrospinal fluid between the inner,

middlemeninges&centralcanalofs.cord,

carries nutrients, acts as a shockabsorber, relayswastebydiffusion& fac.

diffusion, flows within ventricles four

spacesinthebrain
http://www.pbs.org/wnet/brain/3d/http://www.pbs.org/wnet/brain/3d/


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TheHumanBrain

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Fig.49-15


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Speech

Occipital lobe

Vision

Temporal lobe

Frontal lobeParietal lobe

Somatosensoryassociationarea

Frontalassociationarea

Visualassociationarea

Reading

Taste

Hearing

Auditoryassociation

area

Speech

Smell

Fig.49-17


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Generatingwords

Max

Speakingwords

Hearingwords

Seeingwords

Min

Fig.49-1


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TheCerebralCortex

Thecerebralcortexisathin,highlyconvoluted

outer layer of gray matter covering both

hemispheres.

Theprimarymotorarea is in the frontal lobe;

thiscommandsskeletalmuscle.

The primary somatosensory area is dorsal tothecentralsulcusorgroove.

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Forebrain(cerebrum)

contains two hemispheres for

coordinating sensory and motor

informationspeech,

reasoning, memory, personality,which may be located on one side

only

the outer layer is called the cerebralcortex (only1mm thick), deeply folded

intofissures(toincreasesurfacearea)


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Cerebralhemispheres

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Forebrain


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Forebrain

- the two hemispheres are connected by the corpuscallosum allowing info to be shared between the

hemispheres (a collection of nerve fibres) which aresometimes severed to control epilepsy leading tointerestingresults

-thecerebrumcanbesubdividedinto4lobes1. Frontal(walking,speech,intellect,personality),2. temporal(hearing,vision,memory,interpretation),

3. parietal(interpretingsensoryinforeceptors,longtermmemory)and

4. occipital(vision)lobes

Brocas area - a part of the left hemisphereusuallywherespeechcentreislocated

Th l b f b l h i h


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Thelobesofacerebralhemisphere

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Forebrain


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Forebrain

thalamus- below cerebrum, coordinates andinterpretssensoryinfo

hypothalamusbelowthethalamus,relatedtopituitary,

connects endocrine to the nervous system,

receives sensory info, instincts, temperaturecontrol(ANS)

pituitary gland influenced by thehypthalamus, part of the endocrine system

(mastergland) pineal gland part of theendocrine systemmelatoninproduction


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midbrain - less developed in humans than the

forebrain,4spheresrelaycentreforsomeeye

andearreflexes Hindbrain - located behind the midbrain,

connectsbraintospinalcord

contains cerebellum (coordinates movement,

balance,muscletone),Thecerebellumisinvolvedin

learning of new motor skills, such as playing the

piano.

pons (relay station between cerebellum areas, and

cerebellum&medulla)

medulla oblongata (connection between peripheral

and CNS, involuntary movements heart rate,

breathing(ANS),crossoverofcontrol)


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FYI

much brain research takes place during brain

surgery&afterpeoplehavestrokes epileptics also provide insight into braindifferentiationwhentheyundergoseveringofthecorpus callosum to relieve extremely serious

seizures althoughthebrainmustcontroltheentirebody,thevolumeofbrainallocatedtoeachpartofthebodyisnotproportionaltothatbodypartssize

the face and hands account for themajority ofthemotorcortexsattention

Fig.49-16


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Primarysomatosensory cortex

Frontal lobe Parietal lobe

Leg

Genitals

Abdominalorgans

Primarymotor cortex

Toes

Jaw


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LanguageandSpeech

LanguageandspeecharedependentuponBrocasarea(amotorspeech

area)andWernickesarea

(asensoryspeecharea)thatareinvolvedincommunication.

Thesetwoareasarelocatedonlyinthe

lefthemisphere;thelefthemispherefunctionsinlanguageingeneralandnotjustinspeech.

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Languageandspeech

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Organization of the nervous


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Organizationofthenervous

system

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The Spinal Cord


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TheSpinalCordThespinalcordextendsfromthebaseofthe

brainthroughthevertebralcanal.StructureoftheSpinalCordAcentralcanalholdscerebrospinalfluid.

Graymatter of the spinal cord forms an Hand contains interneurons and portions ofsensoryandmotorneurons.

White matter consists of ascending tractstakingsensoryinformationtothebrainanddescending tracts carrying motorinformationfromthebrain.

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ventral root (towards front of body)

carries motor neuron messages to

muscles dorsal root (towards back) carries

sensory neuron messages from the

body

S i l d


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Spinalcord

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FunctionsoftheSpinalCord

Thespinalcordisthecenterformany reflexarcs.

Italsosendssensoryinformationtothebrain

and receivesmotor output from the brain,extendingcommunicationfromthebraintothe peripheral nerves for both control ofvoluntary skeletalmusclesand involuntary

internalorgans.Severingthespinalcordproducesparalysis.

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ThePeripheralNervousSystem

The peripheral nervous system (PNS)contains nerves (bundles of axons) and

ganglia(cellbodies).

Sensory nerves carry information to theCNS,motornervescarryinformationaway

Humanshave12pairsofcranialnervesand

31pairsofspinalnerves.

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Nervestructure

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Cranialnerves

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Thedorsalrootofaspinalnervecontains

sensoryfibersthatconductsensoryimpulsesfromsensoryreceptorstowardthespinalcord.

Dorsalrootganglianearthespinalcordcontainthecellbodiesofsensoryneurons.

Theventralrootofaspinalnervecontainsmotorfibersthatconductimpulsesaway

fromthespinalcordtoeffectors.

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Spinalnerves

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SomaticSystem


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y

The somatic system serves the skin, skeletal

muscles,andtendons.The brain is always involved in voluntary muscleactions but somatic system reflexes areautomatic and may not require involvement of

thebrain. nervesrunningtoskeletalmusclesystem(undervoluntarycontrol)

motor neurons voluntary effectors (skeletalmuscle)

control exists in the cerebrum & cerebellum(coordination)

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Homeostasis and the Autonomic


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HomeostasisandtheAutonomic

NervousSystem

Allautonomicnervesaremotornervesthatregulatetheorgansofthebodywithout

consciouscontrol;involuntary

Controlexistsinthemedulla

Effectorsaresmoothmuscle(digestivesystem),

cardiacmuscle(heart)andglands(exocrine&

endocrine)

Responsibleformaintaininghomeostasisduringtimesofrestandduringemergencies

C i t f t t


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Consistsoftwoparts:Sympathetic

preparesthebodyforstress,includingfightorflightresponse

shortpreganglionicnerve(Ach),longpostganglionicnerve(NEp)

originateinthethoracicvertebrae(ribs)orlumbarvertebrae(smallofback)

Parasympathetic restoresnormalbalance;timesofrelaxation

longpreganglionicnerve(Ach),shortpostganglionicnerve(ACh)

originateinthebrain(cranialnerves)orthespinalcord


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Fig.49-8Parasympathetic division Sympathetic division

Action on target organs:Action on target organs:


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Stimulates glucose

release from liver;

inhibits gallbladder

Dilates pupilof eye

Action on target organs:

Inhibits salivarygland secretion

Accelerates heart

Relaxes bronchiin lungs

Inhibits activityof stomach and

intestines

Inhibits activityof pancreas

Stimulatesadrenal medulla

Inhibits emptyingof bladder

Promotes ejaculation andvaginal contractions

Constricts pupilof eye

Stimulates salivary

gland secretion

Constrictsbronchi in lungs

Slows heart

Stimulates activityof stomach and

intestines

Stimulates activityof pancreas

Stimulatesgallbladder

Promotes emptying

of bladder

Promotes erectionof genitals

Action on target organs:

Cervical

Sympatheticganglia

Thoracic

Lumbar

Synapse

Sacral

Autonomic nervous system


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Autonomicnervoussystem

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DisordersAssociatedWiththeN S


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NervousSystem

ParkinsonsDisease: inadequate

productionofdopamineinthebraincauses

involuntary muscle contractions andtremors; canbe partially alleviatedwith L-

dopa(syntheticdopamine)


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Alzheimers Disease: decrease in CNS

levelsofacetylcholine Multiple Sclerosis: degeneration of theMyelin sheath; Many symptoms, partial

paralysis,doublevision,speechproblems Amyotrophiclateralsclerosis(LouGehrig'sdisease (ALS) : genetic disease causingmotor neurons to die; muscle control islost, increased salivation, cramping,twitching


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Epilepsy:braininjuryorlackofoxygento

thebrain;Seizuresgrandmalorpetitmal

transientlossofmusclecontrol

Spinal Cord Injuries: through injury or

disease,thespinalneuronsaredamaged,

Resultsinlossofmotorcontrol-degreeof

which depends on where the damage

occurred


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Hydrocephalus:wateronthebrainexcesscerebrospinalfluidinthebrain

Increasedpressuremayleadtobrain

damage CerebralPalsy:Usuallycausedbyoxygen

deficiencybefore/duringbirth,reduced

musclecoordination(cerebraldamage)

D Ab


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DrugAbuse

Stimulants increase excitation, anddepressants decrease excitation; eithercanleadtophysicaldependence.

Eachtypeofdrughasbeenfoundtoeitherpromote or prevent the action of aparticularneurotransmitter.

Medications that counter drug effects work

by affecting the release, reception, orbreakdown of dopamine, aneurotransmitterresponsibleformood.

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Drug actions at a synapse


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Drugactionsatasynapse

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Adrugcanaffectaneurotransmitterintheseways:

(a) causeleakageoutofasynapticvesicleintotheaxonbulb;

(b) preventreleaseoftheneurotransmitterintothesynapticcleft;

(c) promotereleaseoftheneurotransmitterintothesynapticcleft;

(d) preventreuptakebythepresynapticmembrane;

(e) blocktheenzymethatcausesbreakdownoftheneurotransmitter;or

(f) bindtoareceptor,mimickingtheactionorpreventingtheuptakeofaneurotransmitter.

Drug use


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Druguse

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Alcohol


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Alcohol may affect the inhibiting transmitter

GABA or glutamate, an excitatoryneurotransmitter.

Alcohol is primarily metabolized in liver and

heavydosescancauseliverscartissueandcirrhosis.

Alcohol is an energy source but it lacksnutrientsneededforhealth.

Cirrhosis of the liver and fetal alcoholsyndromeareseriousconditionsassociatedwithalcoholintake.

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Nicotine


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Nicotine

Nicotineisanalkaloidderivedfromtobacco.

In the CNS, nicotine causes neurons torelease dopamine; in the PNS, nicotine

mimics the activity of acetylcholine andincreases heart rate, bloodpressure, anddigestivetractmobility.

Nicotine induces both physiological andpsychologicaldependence.

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Cocaine


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CocaineCocaineisanalkaloidderivedfromtheshrub

Erythroxylumcocoa,oftensoldaspotentextracttermedcrack.

Cocainepreventsuptakeofdopaminebythe

presynapticmembrane,ishighlylikelytocausephysicaldependence,andrequireshigherdosestoovercometolerance.

Thismakesoverdosingisarealpossibility;

overdosingcancauseseizuresandcardiacarrest.

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Heroin


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Heroin

Derivedfrommorphine,heroinisanalkaloid

ofopium.

Useofheroincauseseuphoria.

Heroin alleviates pain by binding to

receptors meant for the bodys own pain

killerswhicharetheendorphins.

Tolerance rapidly develops and withdrawal

symptomsaresevere.

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Marijuana


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Marijuana

Marijuana is obtained from the plantCannabis sativa that contains a resinrichinTHC(tetrahydrocannabinol).

Effectsincludepsychosisanddeliriumandregularusecanleadtodependence.

Long-term marijuana use may lead to

brain impairment, and a fetal cannabissyndromehasbeenreported.

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Chapter Summary


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ChapterSummary

Thenervoussystemconsistsoftwotypesofcells:neuronsandmesoglia.

Neurons are specialized to carry nerve

impulses.Anerveimpulseisanelectrochemicalchangethattravelsalongthelengthofa

neuronfiber.Transmissionofsignalsbetweenneuronsisdependentonneurotransmittermolecules.

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The central nervous system is made up ofthespinalcordandthebrain.

The parts of the brain are specialized for

particularfunctions.The cerebral cortex contains motor areas,

sensoryareas,andassociationareasthat

areincommunicationwitheachother.The cerebellum is responsible for

maintainingposture;thebrainstemhouses

reflexes for homeostasis.17-93


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The reticular formation contains fibers that

arousethebrainwhenactiveandaccount

forsleepwhentheyareinactive.

The limbic system contains specialized

areas that are involved in higher mental

functionsandemotionalresponses.

Long-term memory depends upon

associationareas that are in contactwith

thelimbicsystem.17-94


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There are particular areas in the lefthemisphere that are involved in language

andspeech.

The peripheral nervous system containsnervesthatconductnerveimpulsestoward

andawayfromthecentralnervoussystem.The autonomic nervous system hassympatheticandparasympatheticdivisionswithcounteractingactivities.

Use of psychoactive drugs such as alcohol,nicotine,marijuana, cocaine, andheroin isd t i t l t th b d

nervous sytem v3

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