AUTONOMICNERVOUSSYSTEM

PhysiologyUnit2

InPhysiologyToday

PeripheralNervousSystemOrganization

SomaticDivision• SingleneuronbetweenCNS

andskeletalmusclecells• Innervatesskeletalmuscle• Canonlyleadtomuscle

excitation

AutonomicDivision• Twoneuronsystem

betweenCNSandeffectororgans

• Innervatessmoothmuscle,cardiacmuscle,glands

• Canbeeitherexcitatoryorinhibitory

AutonomicNervousSystem

• 2neuronsinseriessynapsingataganglia

• Preganglionicneuron– CNStoganglion

• Postganglionicneuron– Gangliontoeffector

SympatheticDivision• FightorFlightresponse• Increasesactivityunderconditionsofphysicalorphysiologicalstress

• Allresourcesforphysicalexertionareactivated– HRincreases– BPincreases– Bloodflowtoskeletalmuscles,heartandbrainincreases

– Liverreleasesglucose– Pupilsdilate– GItractactivityisdampened– Bloodflowtotheskinisreduced

SympatheticDivisionThoracolumbarDivision

• SympatheticneuronsexittheCNSfromthethoracicandlumbarregionsofthespinalcord

• Gangliaarrangedasthesympathetictrunks– Closetothespinalcord– 2chainsoneithersideofthespinalcord

ParasympatheticDivision

• Restanddigestresponse• Homeostaticfunctionsarepredominant

ParasympatheticDivisionCraniosacralDivision

• PreganglionicneuronsexittheCNSfromthebrainstemandsacralregionsofthespinalcord

• Parasympatheticganglialiewithinorveryclosetotheeffectororgansthatthepostganglionicneuronsinnervate

ActivationPatternsoftheDivisions

• SympatheticDivision–Moredivergenceofpreganglionicneurons– Tendstorespondasasingleunit– Increasedsympatheticactivitytendstooccurbodywide

• ParasympatheticDivision– Lessdivergenceofpreganglionicneurons– Specificorgansareactivatedinapatternthatisdependentoneachphysiologicalresponse

NeurotransmittersoftheANS• PreganglionicneuronsreleaseACh• Postganglionicneurons– SympatheticdivisionreleaseNE– ParasympatheticdivisionreleaseACh

• Cotransmittersreleasedbypreganglionicneuronswiththeprimaryneurotransmitteratmanyautonomicganglia– ATP,dopamine,neuropeptides

• Postganglionicneurons– Nitrousoxideforsmoothmuscledilation

AdrenalMedulla

• Postganglionicneuronsthatinnervatetheadrenalmedulladonotdevelopaxons

• Theformtheendocrinegland,theadrenalmedulla

• Onceactivatedbythesympatheticpreganglionicneuron,thecellsoftheadrenalmedullarelease80%Epi,20%NEintotheblood

TransmittersofthePeripheralNervousSystem

DualInnervation

• Theheart,manyglandsandsmoothmuscleareinnervatedbybothdivisionsoftheANS

• Opposingeffects• Divisionsareusuallyactivatedreciprocally– Sympatheticactivityincreases– Parasympatheticactivitydecreases– Visversa

• Providesprecisecontroloftheeffector

CooperativeControl• BothdivisionsoftheANS

operatetogether• Autonomicresponses

resultfromtheregulatedinteractionsofboththeparasymapathetic andsympatheticdivisions

• Autonomicresponsesusuallyoccurwithoutawarenessorconsciouscontrol(autonomous)