Download The Brain

TheBrain-Part1
MammalianBrainDiversity
Observationsofdifferentmammalianbrains
• Commonalities:haveabiggerpartonthetopandasmallerpartonthebottom
o Have‘flaps’and‘grooves’
o Brainsareremarkablysimilarinoverallstructure
• Linearrelationshipbetweenbrainsizeandbodyweight
o Abovetheline,brainisbiggerthanwouldbeexpectedforbodysize(tendto
havemoreabilities)
o Belowtheline,brainissmallerthanwouldbeexpectedforbodysize(tendto
haveless/constrictedabilities)
o Humanshavethebiggestbraingiventheirbodysize
(http://serendip.brynmawr.edu/bb/kinser/Size5.html)
Einstein’sBrain
• Analysisfoundtwoareasweredifferentfromaveragebrains
o Prefrontalcortex(area9)-planning,attention,workingmemory
o ParietalLobe(area39)-association,cortex,language
o InthesetwopartsEinsteinhadmoreglialcellsandmoresulci(grooves)
GivingDirectionsInsideyourBrain
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Neuraxis-tube
Rostral/anterior-front
Ventral-bellyside
Dorsal-backside
Caudal/Posterior-end
Lateral-towardsoutside Medial-towardsinside(midline)
Contralateral-oppositesideofbody
Ipsilateral-samesideofbody
BrainPlanesofSection
• Frontal,coronal,transversesection
• Horizontalsection
• Sagittalsection
• Crosssection(spinalcord)
• Graymatter:cellbodies(somas)
o Towardsoutsideofbrain
o Incenterofspinalcord
• Whitematter:axons(myelinsheaths)
o Middleofbrain
http://homepage.smc.edu/russell_richard/Psych2/Graphics/Brain_directions_planes__sections_1_small.gif
o Onoutsideofspinalcord
NervousSystem:Overview
• Nervoussystem
o CentralNervousSystem:Brain(skull)andSpinalCord(vertebralcolumn/spine)
o PeripheralNervousSystem:NervesandPeripheralGanglia
MeningesandBloodVessels
Meninges • Duramater:thick,unstretchablemembranethatcoversthebrain
• Arachnoidmembrane:soft,spongy(weblike)
o Sub-arachnoid:spacefilledwithCerebroSpinalFluid
• Piamater:Followsbrainsurface,containsbloodvessels
• Smallinfectionofthemeninges:headache,migraine
• Largeinfection:meningitis
• Causaequine(horsetail):backofspinalcord-sciatic
nerve
BrainVasculature
• Brain(2%ofthebody)usesabout20%oftheoxygen
absorbedbythelungs
• Containslargenetworkofcapillaryvessels
• Dense:onecantellwhichgroupofneuronsareactive
bylookingatwherebloodflows(fMRI:glucoseand
oxygen)
• Migraine,stroke-causedbyproblemswiththeblood
vessels
TheCerebrospinalFluidandVentricles
CerebralVentricles
• Ventricles:hollowspacesfilledwithCerebrospinalfluid(CSF)
• Lateralventricles->thirdventricle->cerebralaqueduct->fourthventricle->
subarachnoidspaceandcentralcanal
• CSFproducedbythechoroidplexus(linestheventricles)fromblood
• CSFabsorptioninthesinuses
o Fullyreplacedevery6hours
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Hydrocephalus-preventsCSFflowanditaccumulatesintheventricles,causingthemto
enlarge
o Occursin2/1000children,mostlycongenital(atbirth),alsothoughttobea
resultofmeningitis
o Shunting-insertpumptomakeCSFflow
o Video:throughplasticity,Sharron(whohadhydrocephalus)canregainall
functions,despitehavinghalfabrain
o Note:plasticitytakestime,itwouldn’tbethesameasifanadultweretohaveit
CSFSummary
• Producedfrombloodbythechoroidplexi(all
ventricles)
• Fullreplacementevery6hours
• Flowsallaroundbrainandspinalcord
• Reabsorbedintotheblood
• Ventriclesalsohaveroleindevelopment
• Carriesnutrientsandactsasacushion
DevelopmentalView
NeuralMigration
• On18thday…humansstartasaneuraltubemadeofprogenitorcells
o Createlittlepathwaysonwhichothercellswillclimb
o Growontopofit
o By20weeks,thebrainlooks‘superficially’likeanadultbrain
• Progenitorcellsdivide
o Symmetricaldivision:ProgenitorcellandProgenitorcell->increaseventricular
size
o Asymmetricalcelldivision:ProgenitorcellandBraincell(radialglialcells-
supportmigration,andneurons)->createbraintissue
o Longera/symmetricaldivisionstages=largerbrains
o After5months:Apoptosis-suicidesignalforprogenitorcells(tellscellstostop)
o Ventriclesproduce2Xmoreneuronsthannecessaryandunusedneurons
progressivelydiebyapoptosis
• Thereisneurogenesisintheadultbrain(youcanproducenewneurons)
o Inrats:hippocampus(learningandmemory)andolfactorybulb(senseofsmell)
o Physicalexercisecanincreaseneurogenesis
o Stressanddepressioncanreduceneurogenesis
DevelopmentalStages
• Telencephalon:cognitive+emotionalareas
• Diencephalon:earlysensoryandhormonal
• Mesencephalon:motivation,regulationofbehavior
• Metencephalon:basicmotoractionandplans
• Myelencephalon:interfacewithspinalcord
• Forebrain:telencephalonanddiencephalon(cerebralhemispheres)
• Midbrain:mesencephalon
• Hindbrain:metencephalonandmyelencephalon(medulla)
• Developsfrom4->6subdivisions
Forebrain
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Forebrain=Telencephalon+Diencephalon
Telencephalon=2hemispheres->1hemispheres->cerebralcortex,basalganglia,limbic
system
The3MajorFissures:2hemispheres
• Fissure=fissures
• Sulcus=sulci
• Gyrus=gyri
• Corpuscallosum(rightvs.left)
http://hubel.med.harvard.edu/book/139.jpg
o Contralateral
o Perceptual+motorinfoflow
o Rightsidebrainconnectstotheleftsideofthebodyandviceversa
o Splitbrain:cannotpronouncewhatheseeswithhislefteyebecausethecorpus
callosumisdisconnected
• Braindoesn’thavealotofroomsothesulciandgyriallowforabiggersurfaceina
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