nervous sytem v3
TRANSCRIPT
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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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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
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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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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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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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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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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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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¢ralcanalofs.cord,
carries nutrients, acts as a shockabsorber, relayswastebydiffusion& fac.
diffusion, flows within ventricles four
spacesinthebrain
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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
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Generatingwords
Max
Speakingwords
Hearingwords
Seeingwords
Min
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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
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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
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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