Medlec Histo Nervous System

8/3/2019 Medlec Histo Nervous System

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HISTOLOGYHISTOLOGYNERVOUS SYSTEMNERVOUS SYSTEM

ChonaChona H.H. AragaAraga, M.D., M.D.


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NERVOUS FUNCTIONSNERVOUS FUNCTIONS Bodys master controlling and communicatingBodys master controlling and communicating

systemsystem

Three functionsThree functions

Sensory inputSensory inputGathers informationGathers information

from sensory receptorsfrom sensory receptors

IntegrationIntegration

Processes and interpretsProcesses and interpretssensory inputsensory input

Motor outputMotor output

Activates effector organs to cause a responseActivates effector organs to cause a response


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Nervous SystemNervous System

OrganizationOrganization


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ORGANIZATIONORGANIZATION

Two Principal Parts of the SystemTwo Principal Parts of the System

Central nervous system (CNS)Central nervous system (CNS)

Brain and spinal cordBrain and spinal cord

Integrating and command centerIntegrating and command center Interprets sensory inputInterprets sensory input

Dictates motor responsesDictates motor responses

Peripheral nervous system (PNS)Peripheral nervous system (PNS)

Nerves extending from brain and spinal cordNerves extending from brain and spinal cord

Carry impulses to and from the CNSCarry impulses to and from the CNS


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PERIPHERAL DIVISIONSPERIPHERAL DIVISIONS

Two Functional Subdivisions of the PNSTwo Functional Subdivisions of the PNS

Sensory divisionSensory division

afferent divisionafferent division

Nerve fibers conveying impulses to the CNSNerve fibers conveying impulses to the CNS Somatic afferent fibersSomatic afferent fibers convey impulses from the skin,convey impulses from the skin,

muscles, and jointsmuscles, and joints

Visceral afferent fibersVisceral afferent fibers convey impulses from visceralconvey impulses from visceral

organsorgans

Motor divisionMotor division

, efferent division, efferent division

Nerve fibers conveying impulses from the CNSNerve fibers conveying impulses from the CNS


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ORGANIZATIONORGANIZATION


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HISTOLOGYHISTOLOGYNervous system consists mainly of nervousNervous system consists mainly of nervous

tissuetissue

Highly cellularHighly cellular

e.g.,


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NEUROGLIANEUROGLIA Nerve glueNerve glue

Six types of small cells associated with neuronsSix types of small cells associated with neurons

4 in CNS4 in CNS

2 in PNS2 in PNS

Most have central cell body and branchingMost have central cell body and branching

processesprocesses

Several functionsSeveral functions e.g., Supportive scaffolding for neuronse.g., Supportive scaffolding for neurons

e.g., Electrical isolation of neuronse.g., Electrical isolation of neurons

e.g., Neuron health and growthe.g., Neuron health and growth


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CNS NEUROGLIACNS NEUROGLIA AstrocytesAstrocytes MicrogliaMicroglia

Ependymal cellsEpendymal cells

OligodendrocytesOligodendrocytes


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CNS NEUROGLIACNS NEUROGLIA

AstrocytesAstrocytes Most abundant and versatileMost abundant and versatile glialglial cellscells

Numerous processes support branching neuronsNumerous processes support branching neurons Anchor neurons to capillary blood supplyAnchor neurons to capillary blood supply

Guide migration of young neuronsGuide migration of young neurons Facilitate nutrient delivery to neuronsFacilitate nutrient delivery to neurons

(blood(blood glialglial cellcell neuron)neuron)

Control chemical environmentControl chemical environmentaround neuronsaround neurons Uptake of KUptake of K++, neurotransmitters, neurotransmitters

Communicate withCommunicate with astrocytesastrocytes& neurons& neurons Gap junctionsGap junctions


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ASTROCYTESASTROCYTES

star shaped cells with many branchingstar shaped cells with many branching cytoplasmiccytoplasmic

process,process,

develop fromdevelop from ectodermalectodermal spongioblastsspongioblasts.. nuclei are large, ovoid, spherical, nuclei notnuclei are large, ovoid, spherical, nuclei not

obvious,obvious,

cytoplasm hascytoplasm has golgigolgi complex,complex,

fewfew ribosomesribosomes, little granular reticulum,, little granular reticulum,lysosomes,andlysosomes,and glycogen.glycogen.


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2 types of2 types of

astrocytes:astrocytes: protoplasmic astrocytes = found in gray matterprotoplasmic astrocytes = found in gray matter

of brain, spinal cordwith short thick processes..of brain, spinal cordwith short thick processes..

Fibrous astrocyte = found in white matter, withFibrous astrocyte = found in white matter, with

long slender processes with few branches.long slender processes with few branches.


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MicrogliaMicroglia Small ovoid cellsSmall ovoid cells

Relatively long thornyRelatively long thorny

processesprocesses

Processes touch nearby neuronsProcesses touch nearby neurons

Migrate toward injured neuronsMigrate toward injured neurons

Transform into macrophageTransform into macrophage

PhagocytizePhagocytize microorganisms, debrismicroorganisms, debris (Cells of immune system cannot enter the CNS)(Cells of immune system cannot enter the CNS)


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Ependymal CellsEpendymal Cells Line central cavities of brain and spinal cordLine central cavities of brain and spinal cord

Form permeable barrier between cerebrospinal fluid insideForm permeable barrier between cerebrospinal fluid inside

these cavities and tissue fluid of CNS tissuethese cavities and tissue fluid of CNS tissue

Shapes range from squamous to columnarShapes range from squamous to columnar

Many are ciliatedMany are ciliated

Beating helps circulate cerebrospinal fluid cushioning brainBeating helps circulate cerebrospinal fluid cushioning brain

and spinal cordand spinal cord


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OligodendrocytesOligodendrocytes

Fewer processes than astrocytesFewer processes than astrocytes

Wrap processes tightly around thicker neuronWrap processes tightly around thicker neuron

fibers in CNSfibers in CNS Myelin sheathMyelin sheath

Insulating coveringInsulating covering


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OLIGODENDROCYTESOLIGODENDROCYTES

smaller thansmaller than astrocytesastrocytes..

Develop fromDevelop from spongioblastsspongioblasts ( primary( primary ectodermalectodermalcells)cells)

Fewer thanFewer than astrocytesastrocytes with fewer and shorterwith fewer and shorterprocesses.processes.

Nuclei are small, ovoid, irregular, scantyNuclei are small, ovoid, irregular, scantycytoplasmcytoplasm

On electron microscopy, more dense withOn electron microscopy, more dense withnumerous free and attachednumerous free and attached ribosomesribosomes, extensive, extensive

golgigolgi complexcomplex

Occur mainly in gray matter and among bundles ofOccur mainly in gray matter and among bundles ofaxons in white matter (axons in white matter (interfascicularinterfascicular

oligodendrocytesoligodendrocytes))


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PNS NEUROGLIAPNS NEUROGLIA

Satellite cellsSatellite cells Surround neuron cell bodies within gangliaSurround neuron cell bodies within ganglia

(A ganglion is a collection of nerve cell bodies(A ganglion is a collection of nerve cell bodies

outside of the CNS)outside of the CNS) Function poorly understoodFunction poorly understood


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PNS NEUROGLIAPNS NEUROGLIA

Schwann cellsSchwann cells NeurolemmocytesNeurolemmocytes

Surround and form myelin sheaths around larger nerveSurround and form myelin sheaths around larger nerve

fibers of PNSfibers of PNS

Functionally similar toFunctionally similar to oligodendrocytesoligodendrocytes

Vital to regeneration of peripheral nerve fibersVital to regeneration of peripheral nerve fibers


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NEURONSNEURONS Nerve cellsNerve cells Structural units of nervous systemStructural units of nervous system

Billions are present in nervous systemBillions are present in nervous system

Conduct messages throughout bodyConduct messages throughout body

Nerve impulsesNerve impulses

Extreme longevityExtreme longevity Can function optimally for entire lifetimeCan function optimally for entire lifetime

AmitoticAmitotic Ability to divide is lost in mature cellsAbility to divide is lost in mature cells

Cannot be replaced if destroyedCannot be replaced if destroyed

Some (very few) exceptionsSome (very few) exceptions

e.g., stem cells present in olfactory epithelium can produce new neuronse.g., stem cells present in olfactory epithelium can produce new neurons

Stem cell research shows great promise in repairing damaged neuronsStem cell research shows great promise in repairing damaged neurons

High metabolic rateHigh metabolic rate Require large amounts of oxygen and glucoseRequire large amounts of oxygen and glucose


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NeurotrophinsNeurotrophins

Promote neuron growth.Promote neuron growth.

Nerve growth factors include:Nerve growth factors include:

Nerve growth factor (NGF), brainNerve growth factor (NGF), brain--derived neurotrophic factorderived neurotrophic factor(BDNF), glial(BDNF), glial--derived neurotrophic factor (GDNF),derived neurotrophic factor (GDNF),neurotrophinneurotrophin--3, and neurotrophin3, and neurotrophin--4/5.4/5.

Fetus:Fetus:

Embryonic development of sensory neurons and sympatheticEmbryonic development of sensory neurons and sympatheticganglia (NGF and neurotrophinganglia (NGF and neurotrophin--3).3).

Adult:Adult:

Maintenance of sympathetic ganglia (NGF).Maintenance of sympathetic ganglia (NGF).

Mature sensory neurons need for regeneration.Mature sensory neurons need for regeneration.

Required to maintain spinal neurons (GDNF).Required to maintain spinal neurons (GDNF).

Sustain neurons that use dopamine (GDNF).Sustain neurons that use dopamine (GDNF).

MyelinMyelin--associated inhibitory proteins:associated inhibitory proteins:

Inhibit axon regeneration.Inhibit axon regeneration.


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NeuronsNeurons

Axon of anotherneuron

Cell BodyDendrites

Axon

MyelinSheath

Dendrites ofanother neuron


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NEURONSNEURONS Generally large, complex cellsGenerally large, complex cells Structures vary, but all neurons have the same basicStructures vary, but all neurons have the same basic

structurestructure

Cell bodyCell body

Slender processesSlender processes

extending from cellextending from cell

bodybody

Plasma membranePlasma membrane

is site of signalingis site of signaling


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NEURON CELL BODYNEURON CELL BODY

Most neuron cell bodies are located in the CNSMost neuron cell bodies are located in the CNS Protected by bones of skull or vertebral columnProtected by bones of skull or vertebral column

Clusters of cell bodies in the CNS are termedClusters of cell bodies in the CNS are termed

nucleinuclei Clusters of cellClusters of cell

bodies in thebodies in the

PNS arePNS are

termedtermed

gangliaganglia


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NEURON CELL BODYNEURON CELL BODY

a.k.a., perikaryon or somaa.k.a., perikaryon or soma 55 140140 QQm in diameterm in diameter

Transparent spherical nucleusTransparent spherical nucleus

ContainsContainsconspicuousconspicuous

nucleolusnucleolus


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Perikaryon ( soma)Perikaryon ( soma)

> Formed by the nucleus and surrounding> Formed by the nucleus and surrounding

cytoplasm.cytoplasm.

> Has a receptive function, receives stimuli> Has a receptive function, receives stimuligenerated in other nerve cells.generated in other nerve cells.

> acts as the trophic or nourishing center of the> acts as the trophic or nourishing center of the

cell.cell.


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Perikaryon Perikaryon . Nucleus. Nucleus

large up to 20 um dm.large up to 20 um dm.

euchromatic and spherical, centrally located in somaeuchromatic and spherical, centrally located in soma

chromatin is fine and dispersedchromatin is fine and dispersed

only one large nucleoli indicating active synthesisonly one large nucleoli indicating active synthesis

Barr bodies presentBarr bodies present

Nuclear envelop is distinct with numerous pores.Nuclear envelop is distinct with numerous pores.

With large pale vesicular nucleus and prominent nucleulosWith large pale vesicular nucleus and prominent nucleulos

owls eye.owls eye.


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NEURON CELL BODYNEURON CELL BODY Major biosynthetic center of neuronMajor biosynthetic center of neuron Other usual organelles presentOther usual organelles present

ER &ER & ribosomesribosomes most active and best developed in bodymost active and best developed in body

Sometimes containsSometimes containspigment inclusionspigment inclusions


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NEURON CELL BODYNEURON CELL BODY Focal point for the outgrowth of neuron processesFocal point for the outgrowth of neuron processes

during embryonic developmentduring embryonic development

Some processes receive signalsSome processes receive signals

Plasma membranePlasma membrane

generally also actsgenerally also actsas part of theas part of the

receptive surfacereceptive surface


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Perikaryon.Perikaryon. .. CytoplasmicCytoplasmic organellesorganelles

plasmalemmaplasmalemma is 7is 7 8 nm thick8 nm thick

mitochondria usually small ovoid, or spherical withmitochondria usually small ovoid, or spherical with cristaecristae ofofboth tubular and lamellar type.both tubular and lamellar type.

LargeLarge golgigolgi apparatus &apparatus & parapara--nuclear in position.nuclear in position.

CentriolesCentrioles are prominent with cilium protruding from cellare prominent with cilium protruding from cellsurfacesurface.( nerve cells are incapable of cell division).( nerve cells are incapable of cell division)

PrimaryPrimary lysosomeslysosomes are common, located near aare common, located near a golgigolgiapparatus, associated with hydrolysis of end products ofapparatus, associated with hydrolysis of end products of

cellular metabolismcellular metabolism SecondarySecondary lysosomeslysosomes increase in number with age, someincrease in number with age, some

becomebecome lipofuscinlipofuscin granules.granules.


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PROMINENT FEATURES OFPROMINENT FEATURES OF

NEURONSNEURONS NISSL bodiesNISSL bodies are basophilic component of theare basophilic component of the cytoplasm,cytoplasm,

stained by basic aniline dyesstained by basic aniline dyes

bodies are stack of granular endoplasmic reticulum withbodies are stack of granular endoplasmic reticulum with

associatedassociated polysomespolysomes andand ribosomesribosomes both free andboth free andattached.attached.

Present in dendrites but absent in axon and the axonPresent in dendrites but absent in axon and the axonhillock.hillock.

Axon hillock = clear conical areas at the origin

Axon hillock = clear conical areas at the originof axon from the soma.of axon from the soma.

NisslNissl bodies react to injury by breaking upbodies react to injury by breaking upand diffusing throughout the cytoplasm calledand diffusing throughout the cytoplasm called

chromatolysischromatolysis


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Prominent features ofProminent features of

neuronsneurons NeurofibrilsNeurofibrils

visible by light microscopyvisible by light microscopy

found through out thefound through out the parikaryonparikaryon

extend into dendrites and axons.extend into dendrites and axons. The bundles contain microtubules (The bundles contain microtubules ( neurotubulesneurotubules

25 nm dm ) and microfilaments (25 nm dm ) and microfilaments ( neurofilamentsneurofilaments,,

10 nm dm).10 nm dm).


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Prominent featuresProminent features

of neuronof neuron CytoplasmicCytoplasmic inclusions.inclusions.

fat droplets commonly found infat droplets commonly found in perikaryonperikaryon

glycogen not present in adult neurons.glycogen not present in adult neurons.

Pigments granules various type presentPigments granules various type present

L

ipofuscinL

ipofuscin granules in large neurons.granules in large neurons. Granules are yellow brownGranules are yellow brown

Iron granules present in nerve cells of various regions likeIron granules present in nerve cells of various regions likeinin globusglobus palliduspallidus, tend to increase in number with age., tend to increase in number with age.

Melanin is present in:Melanin is present in:

substantiasubstantia nigranigra of midbrain,of midbrain, spinal and sympathetic gangliaspinal and sympathetic ganglia

LocusLocus ceruleusceruleus in 4th ventricle floor.in 4th ventricle floor.


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NEURON PROCESSESNEURON PROCESSES

Extend from the neurons cell bodyExtend from the neurons cell body CNS contains both neuron cell bodies and theirCNS contains both neuron cell bodies and their

processesprocesses

Bundles of CNS processes are termed tractsBundles of CNS processes are termed tracts PNS consists mainly of neuronal processesPNS consists mainly of neuronal processes

Bundles of PNS processes are termed nervesBundles of PNS processes are termed nerves

Two types of neuron processesTwo types of neuron processes DendritesDendrites

AxonsAxons


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Nerve cellNerve cell

processes.processes.

Dendrites = nerve cells of sensory ganglia (Dendrites = nerve cells of sensory ganglia ( uniuniand bipolar) have a single dendrite thatand bipolar) have a single dendrite thatresembles an axon.resembles an axon.

> main stem dendrites contain> main stem dendrites contain nisslnissl bodies.bodies.

> contains microtubules and filaments> contains microtubules and filaments

> involved in transport of organelles> involved in transport of organelles

> contains> contains dendriticdendritic spines specialized forspines specialized forsynaptic contacts.synaptic contacts.


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Typical DendriteTypical Dendrite Short, tapering, diffusely branching extensionsShort, tapering, diffusely branching extensions

Generally hundreds clustering close to cell bodyGenerally hundreds clustering close to cell body

Most cell body organelles also present in dendritesMost cell body organelles also present in dendrites

Main receptive / input regionsMain receptive / input regions Large surface area forLarge surface area for

receiving signals fromreceiving signals fromother neuronsother neurons

Convey incoming messagesConvey incoming messages

toward cell bodytoward cell body

ShortShort--distance signals aredistance signals aregraded potentialsgraded potentialsNot action potentialsNot action potentials


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Nerve cellNerve cell

processes.processes. Axon = the axis cylinder, single, arising fromAxon = the axis cylinder, single, arising from

the nerve cell body calledAxon hillockthe nerve cell body calledAxon hillock with smooth contour and are of uniform diameterwith smooth contour and are of uniform diameter

more slender and straightermore slender and straighter usually terminates in twig like branchingusually terminates in twig like branching--

telodendritestelodendrites

TelodendritesTelodendrites contact thecontact the perikaryonperikaryon, dendrites, dendrites

oraxonoraxon of one or more neurons at synapses.of one or more neurons at synapses. BoutonsBoutons terminauxterminaux = small swellings at the axonal= small swellings at the axonaltwigs at thetwigs at the terminationofterminationof aa myelinatedmyelinated axon.axon.

BoutonsBoutons or passant = swellings at the synapses ofor passant = swellings at the synapses ofterminal axons.terminal axons.


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TypicalAxonTypicalAxon Single axon per neuronSingle axon per neuron

Axon hillock of cell body narrows to form a slenderAxon hillock of cell body narrows to form a slender

process of uniform diameterprocess of uniform diameter

Sometimes very shortSometimes very short

Sometimes very longSometimes very long

e.g., axons controllinge.g., axons controlling

big toe are 3big toe are 3 4 feet4 feetlonglong


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TypicalAxonTypicalAxon Single axon may branch along lengthSingle axon may branch along length

Axon collaterals extend from neurons at ~ 90Axon collaterals extend from neurons at ~ 90oo anglesangles

Usually branchesUsually branches

profusely at endprofusely at end

10,000 or more10,000 or more

terminal branchesterminal branches

is commonis common

Distal endingsDistal endings

termed axonaltermed axonal

terminalsterminals


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TypicalAxonTypicalAxon Conducting component of neuronConducting component of neuron

Generates nerve impulsesGenerates nerve impulses

Generated at axon hillock / axon junction in motor neuronsGenerated at axon hillock / axon junction in motor neurons

Trigger zoneTrigger zone

Transmits nerveTransmits nerve

impulses away fromimpulses away from

cell bodycell body To axonal terminalsTo axonal terminals


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TypicalAxonTypicalAxon Axonal terminals areAxonal terminals are secretory componentsecretory component of neuronof neuron

Sequence of eventsSequence of events

Signal reaches terminalsSignal reaches terminals

Membranes of vesicles fuse withMembranes of vesicles fuse with

plasma membraneplasma membrane

AxolemmaAxolemma

Neurotransmitters releasedNeurotransmitters released

Neurotransmitters interactNeurotransmitters interact

with either other neuronswith either other neurons

or effector cellsor effector cells

Excite or inhibitExcite or inhibit


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TypicalAxonTypicalAxon Contains most of the same organelles found in dendritesContains most of the same organelles found in dendrites

and cell bodyand cell body

Lacks ER and Golgi apparatusLacks ER and Golgi apparatus


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TypicalAxonTypicalAxon Rely on cell body for some moleculesRely on cell body for some molecules

Rely on efficient transport mechanisms for deliveryRely on efficient transport mechanisms for delivery

AnterogradeAnterograde movement toward axonal terminalsmovement toward axonal terminals

e.g., Mitochondria,e.g., Mitochondria,

membrane components,membrane components,

neurotransmitters orneurotransmitters or

enzymes required forenzymes required for

neurotransmitterneurotransmitter

synthesis, etc.synthesis, etc.

RetrogradeRetrograde movementmovement

toward cell bodytoward cell body

e.g., Organelles beinge.g., Organelles being

returned for recyclingreturned for recycling


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TypicalAxonTypicalAxon Some viruses and bacterial toxins use retrogradeSome viruses and bacterial toxins use retrograde

transport to reach the cell bodytransport to reach the cell body

e.g., poliovirus, rabies virus, herpes simplex viruses, tetanuse.g., poliovirus, rabies virus, herpes simplex viruses, tetanus

toxin, etc.toxin, etc.

Such viruses can beSuch viruses can be

used as vehicles for theused as vehicles for the

therapeutic delivery oftherapeutic delivery of

engineered DNAengineered DNA

Gene therapyGene therapy


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MYELIN SHEATHMYELIN SHEATH

Whitish, fatty covering of many nerve fibersWhitish, fatty covering of many nerve fibers Particularly those long are large in diameterParticularly those long are large in diameter

Protects and electrically insulates fibersProtects and electrically insulates fibers

Increases speed of nerve impulse transmissionIncreases speed of nerve impulse transmission Some axons and all dendrites are unmyelinatedSome axons and all dendrites are unmyelinated


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In PNS, myelin sheaths formed by Schwann cellsIn PNS, myelin sheaths formed by Schwann cells Continually wrap around nerveContinually wrap around nerve

Cytoplasm gradually squeezed from intracellular spaceCytoplasm gradually squeezed from intracellular space

Result is many concentric layers of plasma membraneResult is many concentric layers of plasma membrane

surrounding the axonsurrounding the axon These plasma membranes contain little proteinThese plasma membranes contain little protein

Some proteins present interlock adjacent membranesSome proteins present interlock adjacent membranes

Thickness depends on number of wrappingsThickness depends on number of wrappings

Nucleus and most ofNucleus and most ofcytoplasm exist as a bulgecytoplasm exist as a bulge

external to the myelin sheathexternal to the myelin sheath

NeurilemmaNeurilemma


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Adjacent Schwann cells on axon do not touchAdjacent Schwann cells on axon do not toucheach othereach other

Gaps in sheath occur at regular intervalsGaps in sheath occur at regular intervals

Nodes of RanvierNodes of Ranvier

a.k.a., Neurofibrila.k.a., Neurofibril

nodesnodes

Axon collateralsAxon collaterals

can emerge atcan emerge at

these nodesthese nodes


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CNS contains both myelinated and unmyelinatedCNS contains both myelinated and unmyelinatedaxonsaxons

Those long are large in diameter are typicallyThose long are large in diameter are typically

myelinatedmyelinated

Oligodendrocytes, not Schwann cells, form CNSOligodendrocytes, not Schwann cells, form CNS

myelin sheathsmyelin sheaths

Oligodendrocytes possess numerous processes thatOligodendrocytes possess numerous processes that

can coil around numerous (up to 60) axons at oncecan coil around numerous (up to 60) axons at onceCNS myelin sheaths lack a neurilemmaCNS myelin sheaths lack a neurilemma


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Myelination of Axons by Oligodendrocytes


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White matterWhite matter Regions of the brain and spinal cord containingRegions of the brain and spinal cord containing

dense collections of myelinated fibersdense collections of myelinated fibers

Gray matterGray matter

Regions of the brain and spinal cord containingRegions of the brain and spinal cord containing

mostly nerve cell bodies and unmyelinated fibersmostly nerve cell bodies and unmyelinated fibers


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NEURON CLASSIFICATIONNEURON CLASSIFICATION

Structural classification based upon number ofStructural classification based upon number ofprocessesprocesses

Multipolar neuronsMultipolar neurons

Bipolar neuronsBipolar neurons

Unipolar neuronsUnipolar neurons

Functional classification based upon directionFunctional classification based upon direction

nerve impulse travelsnerve impulse travels

Sensory (afferent) neuronsSensory (afferent) neurons

Motor (efferent) neuronsMotor (efferent) neurons

Interneurons (association neurons)Interneurons (association neurons)


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Structural ClassificationStructural Classification Multipolar neuronsMultipolar neurons

Three or more processesThree or more processes

Most common neuronMost common neurontype in humanstype in humans

(> 99% of neurons)(> 99% of neurons)

Bipolar neuronsBipolar neurons

Two processesTwo processes axon andaxon anddendritedendrite

Found only in someFound only in somespecial sense organsspecial sense organs

e.g., retina of eyee.g., retina of eye

Act as receptor cellsAct as receptor cells

Unipolar neuronsUnipolar neurons

Single short processSingle short process

Pseudounipolar neuronsPseudounipolar neurons Originate as bipolar neuronsOriginate as bipolar neurons

Two processes converge andTwo processes converge andfusefuse

Process divides into proximalProcess divides into proximaland distal branchesand distal branches

Distal process often associatedDistal process often associatedwith a sensory receptorwith a sensory receptor

Peripheral processPeripheral process

Central process enters CNSCentral process enters CNS

Most are sensory neurons inMost are sensory neurons inPNSPNS

C f t fC f t f


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Classification ofClassification of

neurons by shapeneurons by shape


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Functional ClassificationFunctional Classification Sensory (afferent) neuronsSensory (afferent) neurons

Transmit impulsesTransmit impulses towardtowardCNSCNS

From sensory receptors or internalFrom sensory receptors or internalorgansorgans

Most are unipolarMost are unipolar

Cell bodies are located outsideCell bodies are located outsideCNSCNS

Motor (efferent) neuronsMotor (efferent) neurons

Carry impulsesCarry impulses away fromaway from CNSCNS Toward effector organsToward effector organs

MultipolarMultipolar

Cell bodies generally located inCell bodies generally located inthe CNSthe CNS

InterneuronsInterneurons a.k.a., associationa.k.a., associationneuronsneurons

Lie between motor andLie between motor andsensory neurons insensory neurons in

neural pathwaysneural pathways Shuttle signals throughShuttle signals through

CNS pathways whereCNS pathways whereintegration occursintegration occurs

> 99% of neurons in> 99% of neurons inbodybody

Most are multipolarMost are multipolar

Most are confinedMost are confinedwithin the CNSwithin the CNS


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NEUROPHYSIOLOGYNEUROPHYSIOLOGY

Neurons are highly irritableNeurons are highly irritable Responsive to stimuliResponsive to stimuli

Response to stimulus is action potentialResponse to stimulus is action potential

Electrical impulse carried along length of axonElectrical impulse carried along length of axon Always the same regardless of stimulusAlways the same regardless of stimulus

The underlying functional feature of the nervousThe underlying functional feature of the nervous

systemsystem


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ION CHANNELSION CHANNELS

Plasma membranes contain various ion channelsPlasma membranes contain various ion channels Passive channels (leakage channels)Passive channels (leakage channels)

Always openAlways open

Active channels (gated channels)Active channels (gated channels) LigandLigand--gated channelsgated channels

Open when specific chemical bindsOpen when specific chemical binds

VoltageVoltage--gated channelsgated channels

Open and close in response to membrane potentialOpen and close in response to membrane potential

MechanicallyMechanically--gated channelsgated channels

Open in response to physical deformation of receptorOpen in response to physical deformation of receptor

e.g., touch and pressure receptorse.g., touch and pressure receptors


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MEMBRANE POTENTIALSMEMBRANE POTENTIALS

A voltage exists across the plasma membraneA voltage exists across the plasma membrane Due to separation of oppositely charged ionsDue to separation of oppositely charged ions

Potential difference in a resting membrane isPotential difference in a resting membrane is

termed itstermed its

resting membrane potential

resting membrane potential ~~ --70 mV in a resting70 mV in a resting

neuronneuron

Membrane isMembrane is

polarizedpolarized


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MEMBRANE POTENTIALSMEMBRANE POTENTIALS

Neurons use changes in membrane potentials asNeurons use changes in membrane potentials assignalssignals

Used to receive, integrate, and send signalsUsed to receive, integrate, and send signals

Changes in membrane potentials produced byChanges in membrane potentials produced by

Anything changing membrane permeability to ionsAnything changing membrane permeability to ions

Anything altering ion concentrationsAnything altering ion concentrations

Two types of signalsTwo types of signals

Graded potentialsGraded potentialsShortShort--distance signalsdistance signals

Action potentialsAction potentials

LongLong--distance signalsdistance signals


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ACTION POTENTIALSACTION POTENTIALS

Conduction VelocitiesConduction Velocities Conduction velocities of neurons vary widelyConduction velocities of neurons vary widely

Rate of impulse propagation dependent uponRate of impulse propagation dependent upon

Axon diameterAxon diameterLarger axons conduct impulses fasterLarger axons conduct impulses faster

Degree of myelinationDegree of myelination

Myelin sheath dramatically increases rate of propagationMyelin sheath dramatically increases rate of propagation

Myelin acts as an insulator to prevent almost all leakage fromMyelin acts as an insulator to prevent almost all leakage fromaxonaxon


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ACTION POTENTIALSACTION POTENTIALS

Multiple Sclerosis (MS)Multiple Sclerosis (MS) Autoimmune disease mainly affecting youngAutoimmune disease mainly affecting young

adultsadults

Myelin sheaths in CNS are gradually destroyedMyelin sheaths in CNS are gradually destroyed Interferes with impulse conductionInterferes with impulse conduction

Visual disturbances, muscle control problems,Visual disturbances, muscle control problems,

speech disturbances, etc.speech disturbances, etc.

Some modern treatments showing some promiseSome modern treatments showing some promise

in delaying problemsin delaying problems


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NERVE FIBERSNERVE FIBERS

Classified based onClassified based on DiameterDiameter

Degree of myelinationDegree of myelination

Conduction speedConduction speed


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NERVE FIBER CLASSIFICATIONNERVE FIBER CLASSIFICATION

Group A fibersGroup A fibers Largest diameterLargest diameter

Thick myelin sheathsThick myelin sheaths

Conduct impulses at high speeds (> 300 mph)Conduct impulses at high speeds (> 300 mph)

Mostly somatic sensory ad motor fibers serving skin, skeletalMostly somatic sensory ad motor fibers serving skin, skeletal

muscles, and jointsmuscles, and joints Group B fibersGroup B fibers

Intermediate diameterIntermediate diameter

Lightly myelinatedLightly myelinated

Transmit impulses at moderate speeds (40 mph)Transmit impulses at moderate speeds (40 mph)

Group C fibersGroup C fibers Smallest diameterSmallest diameter

UnmyelinatedUnmyelinated

Transmit impulses comparatively slowly (2 mph or less)Transmit impulses comparatively slowly (2 mph or less)

Nerve FiberNerve Fiber


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ClassificationClassification

General classification scheme (ErlangerGeneral classification scheme (Erlanger--Gasser):Gasser):

A fibers: MyelinatedA fibers: Myelinated

Subtypes:Subtypes: EFKHEFKHsome overlap in rangessome overlap in ranges Fastest conducting and largest diameterFastest conducting and largest diameter EEm/sec,m/sec, QQ

A often dropped: alpha motor neuronA often dropped: alpha motor neuron

B fibers: Slower myelinated (seldom used)B fibers: Slower myelinated (seldom used)

C fibers: UnmyelinatedC fibers: Unmyelinated

Slower conducting than As and smallest diameter (0.5 m/sec, 0.5Slower conducting than As and smallest diameter (0.5 m/sec, 0.5 QQ))



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ClassificationClassification

Sensory nerve classification (LloydSensory nerve classification (Lloyd--Hunt):Hunt):

I, II, III fibers: MyelinatedI, II, III fibers: Myelinated

Subtypes: Ia, IbSubtypes: Ia, IbFastest conducting and largest diameterFastest conducting and largest diameter IaIa

IV fibers: UnmyelinatedIV fibers: Unmyelinated

Slower conducting than IIIs and smallest diameterSlower conducting than IIIs and smallest diameter


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SYNAPSESYNAPSE

Junction mediating information transfer from oneJunction mediating information transfer from one

neuron to another neuron or an effector cellneuron to another neuron or an effector cell

Axodendritic synapsesAxodendritic synapses

Axonal endingsAxonal endings dendrites of second neurondendrites of second neuron

Axosomatic synapsesAxosomatic synapses Axonal endingsAxonal endings cell body of neuroncell body of neuron

Presynaptic neuronPresynaptic neuron Conducts impulses toward the synapseConducts impulses toward the synapse

Postsynaptic neuronPostsynaptic neuron

Transmits impulse away from the synapseTransmits impulse away from the synapse


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SYNAPSE TYPESSYNAPSE TYPES

Electrical SynapsesElectrical Synapses Less common than chemical synapsesLess common than chemical synapses

Correspond to gap junctions found elsewhereCorrespond to gap junctions found elsewhere

Cytoplasm of adjacent neurons connected throughCytoplasm of adjacent neurons connected throughprotein channelsprotein channels

Ions flow directly between neuronsIons flow directly between neurons

Transmission across synapse is very rapidTransmission across synapse is very rapid


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SYNAPSE TYPESSYNAPSE TYPES

Chemical SynapsesChemical Synapses Specialized for release & reception ofSpecialized for release & reception of

neurotransmittersneurotransmitters

Two partsTwo parts

Axonal terminal of presynaptic neuronAxonal terminal of presynaptic neuron

Contains numerous synaptic vesicles filled withContains numerous synaptic vesicles filled withneurotransmitter moleculesneurotransmitter molecules

Neurotransmitter receptor regionNeurotransmitter receptor region

Present on dendrite or cell body of postsynaptic neuronPresent on dendrite or cell body of postsynaptic neuron

Separated by synaptic cleftSeparated by synaptic cleft

Remember this stuff in muscles?Remember this stuff in muscles?


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SYNAPSESYNAPSE

Nerve impulse reaches axonal terminalNerve impulse reaches axonal terminal VoltageVoltage--gated Cagated Ca2+2+ channels open in axonchannels open in axon

CaCa2+2+ enters presynaptic neuronenters presynaptic neuron

Neurotransmitter is released via exocytosisNeurotransmitter is released via exocytosis

Vesicles fuse with axonal membraneVesicles fuse with axonal membrane

Neurotransmitter binds to postsynaptic receptorsNeurotransmitter binds to postsynaptic receptors

Ion channels open inIon channels open in

postsynaptic membranepostsynaptic membrane Result is excitation orResult is excitation or

inhibitioninhibition


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SYNAPSESYNAPSE

Binding of neurotransmitter to its receptor isBinding of neurotransmitter to its receptor isreversiblereversible

Permeability affected as long as neurotransmitterPermeability affected as long as neurotransmitter

is bound to its receptoris bound to its receptor

Neurotransmitters do not persist in the synapticNeurotransmitters do not persist in the synaptic

cleftcleft

Degraded by enzymes associated with postsynapticDegraded by enzymes associated with postsynaptic

membranemembrane

Reuptake by astrocytes or presynaptic terminalReuptake by astrocytes or presynaptic terminal

Diffusion of neurotransmitters away from synapseDiffusion of neurotransmitters away from synapse


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NEUROTRANSMITTERSNEUROTRANSMITTERS

More than fifty neurotransmitters identifiedMore than fifty neurotransmitters identified Most neurons make two or moreMost neurons make two or more

Can be released singly or togetherCan be released singly or together

Classification by StructureClassification by Structure

Acetylcholine (ACh)Acetylcholine (ACh)

Biogenic aminesBiogenic amines

Amino acidsAmino acids PeptidesPeptides

ATPATP

Dissolved gasesDissolved gases

Classification by FunctionClassification by Function

Excitatory/InhibitoryExcitatory/Inhibitory

Direct/IndirectDirect/Indirect


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NEURAL INTEGRATIONNEURAL INTEGRATION

Neurons function in groups, not singlyNeurons function in groups, not singly These various components must interactThese various components must interact

Multiple levels of neural integrationMultiple levels of neural integration


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NEURONAL POOLSNEURONAL POOLS

Neurons in CNS are organized into poolsNeurons in CNS are organized into pools Functional groupsFunctional groups

Integrate incoming informationIntegrate incoming information

Forward processed informationForward processed information


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NEURONAL POOLSNEURONAL POOLS

Simple Neuronal PoolSimple Neuronal Pool Incoming fiber branches profusely upon entering poolIncoming fiber branches profusely upon entering pool

EPSPs induced in multiple postsynaptic neuronsEPSPs induced in multiple postsynaptic neurons

EPSPs exceed threshold in some neuronsEPSPs exceed threshold in some neurons

Mainly those with multiple synaptic contactsMainly those with multiple synaptic contacts

EPSPs do not exceedEPSPs do not exceed

threshold in somethreshold in some

neuronsneurons Mainly those withMainly those with

fewer synaptic contactsfewer synaptic contacts

Some close to thresholdSome close to threshold

Facilitated zoneFacilitated zone


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TYPES OF CIRCUITSTYPES OF CIRCUITS

Patterns of synaptic connections in neuronalPatterns of synaptic connections in neuronalpools are called circuitspools are called circuits

Determine neuronal pools functional capabilitiesDetermine neuronal pools functional capabilities

Four basic circuit patternsFour basic circuit patterns Diverging circuitsDiverging circuits

Converging circuitsConverging circuits

Reverberating (oscillating) circuitsReverberating (oscillating) circuits

Parallel afterParallel after--discharge circuitsdischarge circuits


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Diverging (Amplifying) CircuitDiverging (Amplifying) Circuit One incoming fiber triggers responses in everOne incoming fiber triggers responses in ever--

increasing numbers of neuronsincreasing numbers of neurons

Common in both sensory and motor systemsCommon in both sensory and motor systems


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Converging CircuitsConverging Circuits Pool receives inputs from several neuronsPool receives inputs from several neurons

Circuit has funneling effectCircuit has funneling effect

Common in sensoryCommon in sensoryand motor systemsand motor systems


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Reverberating (Oscillating) CircuitsReverberating (Oscillating) Circuits Incoming signal travels through chain of neuronsIncoming signal travels through chain of neurons

Each neuron makes synapses with neuronsEach neuron makes synapses with neurons

upstream in the pathwayupstream in the pathway Involved in rhythmic activities (e.g., breathing)Involved in rhythmic activities (e.g., breathing)


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Parallel AfterParallel After--Discharge CircuitsDischarge Circuits Incoming fiber stimulated parallel neuron arraysIncoming fiber stimulated parallel neuron arrays

Parallel arrays ultimately stimulate a commonParallel arrays ultimately stimulate a common

output celloutput cell Create prolonged burst of impulsesCreate prolonged burst of impulses

Involved in complexInvolved in complex

mental processingmental processing


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PROCESSING PATTERNSPROCESSING PATTERNS

Serial input processingSerial input processing Input travels along one pathway to a specificInput travels along one pathway to a specific

destinationdestination

AllAll--oror--nothing function of systemnothing function of system

e.g., reflexese.g., reflexes

Parallel input processingParallel input processing

Inputs are segregated into multiple pathwaysInputs are segregated into multiple pathways

Integrated in different CNS regionsIntegrated in different CNS regionsDifferent circuits do different things with inputDifferent circuits do different things with input

Not repetitiousNot repetitious

MICROSCOPIC STRUCTUREMICROSCOPIC STRUCTURE


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MICROSCOPIC STRUCTUREMICROSCOPIC STRUCTURE

OF THE CEREBRAL CORTEXOF THE CEREBRAL CORTEX

The cerebral cortex contain 3 main types of neuronThe cerebral cortex contain 3 main types of neuron1. Pyramidal cells1. Pyramidal cells

triangular shapetriangular shape

-- apical dendrites reaching from the upper end towardsapical dendrites reaching from the upper end towards

the cortical surfacethe cortical surface-- basilar dendrites extending horizontally from the cellbasilar dendrites extending horizontally from the cell

bodybody

2.2. StellateStellate neuronsneurons

-- star shapestar shape-- dendrites extending in all directionsdendrites extending in all directions

3.3. FusiformFusiform neuronsneurons

--found in the deeper layersfound in the deeper layers

-- large dendrites ascend towards the cortical surfacelarge dendrites ascend towards the cortical surface


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The axons of the pyramidal and fusiform neurons formThe axons of the pyramidal and fusiform neurons formthe projection and association fibers ; with the largethe projection and association fibers ; with the large

layer V pyramidal neurons projecting their axons to thelayer V pyramidal neurons projecting their axons to the

spinal cord and brainstemspinal cord and brainstem

Smaller layers II and III pyramidal cells sendSmaller layers II and III pyramidal cells sendassociation axons to other cortical areasassociation axons to other cortical areas

Stellate neurons are interneurons whose axons remainStellate neurons are interneurons whose axons remain

within the cortexwithin the cortex

LAYERS OF THE CEREBRALLAYERS OF THE CEREBRAL


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CORTEXCORTEX1.1. MolecularMolecular layer / layer Ilayer / layer I

--outermost layeroutermost layer--contains noncontains non--specific afferentspecific afferent fibersfibers that come from within the cortex or from thethat come from within the cortex or from thethalamusthalamus

2. External granular / layer II2. External granular / layer II

--dense layer of small cellsdense layer of small cells

3. External pyramidal / layer III3. External pyramidal / layer III

--containing pyramidal cells frequently in row formationcontaining pyramidal cells frequently in row formation4. Internal granular / layer IV4. Internal granular / layer IV

--thin layer with cells similar to those of external granular layerthin layer with cells similar to those of external granular layer

--receives afferentreceives afferent fibersfibers from the thalamusfrom the thalamus

5. Internal pyramidal / layer V5. Internal pyramidal / layer V

--containing fewer pyramidal cells but larger in sizes than those of externalcontaining fewer pyramidal cells but larger in sizes than those of external

pyramidal layerpyramidal layer--cells project to distal structure (cells project to distal structure (egeg. Spinal cord, brainstem). Spinal cord, brainstem)

6.6. FusiformFusiform or multiform / layer VIor multiform / layer VI

-- irregularirregular fusiformfusiform cells whose axons enter the adjacent white mattercells whose axons enter the adjacent white matter

B l liB l li


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Basal gangliaBasal ganglia

-- masses of gray matter deep within themasses of gray matter deep within the

cerebral hemispherescerebral hemispheres-- plays an essential functional role in motorplays an essential functional role in motorcontrol.control.

Parts ofB

asal ganglia:Parts ofB

asal ganglia:1.1. Caudate nucleusCaudate nucleus

2.2. PutamenPutamen

3.3. GlobusGlobus palliduspallidus

Sheets ofSheets of myelinatedmyelinated fibersfibers of internal capsuleof internal capsulerun between the nuclei imparting a stripedrun between the nuclei imparting a stripedappearance thus the name corpus striatumappearance thus the name corpus striatum


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FastigealFastigeal nucleusnucleus


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gg

-- Most medial; contains small and largeMost medial; contains small and large multipolarmultipolar

neuronsneuronsGloboseGlobose nucleusnucleus

-- lateral tolateral to fastigealfastigeal and medial toand medial to emboliformemboliform containscontains

small and largesmall and large multipolarmultipolar neuronsneurons

EmboliformEmboliform nucleusnucleus wedge shaped masswedge shaped mass

-- Located close to theLocated close to the hilushilus of dentate nucleusof dentate nucleus

--composed mostly of largecomposed mostly of large multipolarmultipolar neurnsneurnsDentate nucleusDentate nucleus-- largest and most laterallargest and most lateral

crumpled bag appearance; large crumpled bag appearance; large multipolarmultipolarneuronsneurons

Cerebellar cortex


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Molecular layer : contains1-Cells : molecular cells (stellatecells) & basket cells.2-Nerve Fibres :a- dendrites of Purkinje cells(arborisations).b-axons of granule cells. (bifurcate to produce 2-parallelfibres , oriented along long axisof folium).

c-ending of climbing fibers.

Purkinje cell layer : it isformed of one layer (unicellular) oflarge flask-shaped purkinje cells.Their arborisations are at rightangles to long axis to folium.

Granular layer : it is formed ofsmall granule cells & ending of

mossy fibres.

High mag of the Purkinje Cells of the


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High mag of the Purkinje Cells of theCerebellum

SS


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Spinal cordSpinal cord

surrounded by Pia Matter which extends into thesurrounded by Pia Matter which extends into the

anterior median fissure.anterior median fissure.

Centrally is an HCentrally is an H--shaped area of gray mattershaped area of gray mattercompose of nerve cells.compose of nerve cells.

The limbs of the H are called anterior andThe limbs of the H are called anterior andposterior horn. The central canal lies at theposterior horn. The central canal lies at thehorizontal bar of the H.horizontal bar of the H.

The white matter is divided by into longitudinalThe white matter is divided by into longitudinalcolumns by the FUNICULI.columns by the FUNICULI.

Zone of Lissauer = small area containing fineZone of Lissauer = small area containing finenerve cells, between the tips of the posterior hornnerve cells, between the tips of the posterior hornand the surface of the cord.and the surface of the cord.


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Peripheral nervesPeripheral nerves


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Peripheral nervesPeripheral nerves

composed of bundles of nerve fibers are held together bycomposed of bundles of nerve fibers are held together byconnective tissue.connective tissue.

Appear as white due toAppear as white due to myelinatedmyelinated fibers.fibers.

EpineuriumEpineurium = capsule of connective tissue sheath around= capsule of connective tissue sheath arounda nerve, composed of fibroblasts anda nerve, composed of fibroblasts and collagenouscollagenous fibers,fibers,

longitudinal and elastic fibers, major blood vessels.longitudinal and elastic fibers, major blood vessels. Fascicles = bundles within anFascicles = bundles within an epineuriumepineurium..

PerineuriumPerineurium = connective tissue sheath around each= connective tissue sheath around eachfascicle, formed by concentric layers of flattenedfascicle, formed by concentric layers of flattenedfibroblastfibroblast--like cells one cell thick. It islike cells one cell thick. It is continouscontinous with thewith thepiapia arachnoidarachnoid membrane of the CNS. Provides a barriermembrane of the CNS. Provides a barrierto the passage of materials into or out of the nerveto the passage of materials into or out of the nerve

fascicle.fascicle.

EndoneuriumEndoneurium = strands of delicate connective tissue= strands of delicate connective tissue

extending around and between individual nerve fibers.extending around and between individual nerve fibers.

Nerve 10x


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NERVE 40X


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GangliaGanglia


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GangliaGanglia a collection of nerve cell bodies located outside thea collection of nerve cell bodies located outside the

central nervous system.central nervous system.

Types of ganglia:Types of ganglia:

CraniospinalCraniospinal ganglia ( sensory)ganglia ( sensory)

Autonomic nerve system (visceral, motor ganglia)Autonomic nerve system (visceral, motor ganglia)

vary in size and shape with few nerve cell bodies tovary in size and shape with few nerve cell bodies tolarge one up to 50,000 or more cells.large one up to 50,000 or more cells.

Satellite cells = capsule of single layer ofSatellite cells = capsule of single layer of cuboidalcuboidalcellscells

Fish eye nucleusFish eye nucleus

Low magnification of a Ganglion


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Spinal Ganglion w/ cell bodies and nerve


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fibers

Cell Body w/ Nissl and surrounding


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Satellite Cells

Sympathetic ganglion w/ lipofuschin


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pigment

Membranes and vessels ofMembranes and vessels of


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CNSCNS

Dura matter orDura matter or pachymenninxpachymenninx = fibrous tough and= fibrous tough and

inelastic, lines the cranium and attached firmly to theinelastic, lines the cranium and attached firmly to the

bone. Separated from the bone by an epidural orbone. Separated from the bone by an epidural or

extraduralextradural space.space. Composed of the:Composed of the:

FalxFalx cerebriicerebrii= separate the 2 cerebral hemisphere= separate the 2 cerebral hemisphere

TentoriumTentorium cerebellicerebelli= horizontal, between the occipital lobes of= horizontal, between the occipital lobes of

cerebrum above and below the cerebellum.cerebrum above and below the cerebellum.

FalxFalx cerebellicerebelli= between= between cerebellarcerebellar hemisphereshemispheres

Membranes andMembranes and


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vessels..vessels..

Arachnoid membrane = the middle layer,Arachnoid membrane = the middle layer,

composed of fine cobweb like strands ofcomposed of fine cobweb like strands of

interlacing reticular fibers. The thin, delicate,interlacing reticular fibers. The thin, delicate,

nonvascular membrane that lines the dura.nonvascular membrane that lines the dura.

Has a space subarachnoid spacebetweenHas a space subarachnoid spacebetween

trabeculaetrabeculae

Membranes andMembranes and


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vessels.vessels. Pia matter = the innermost layer, with blood vesselsPia matter = the innermost layer, with blood vessels

supplying the CNS, single layered leptomeninnx orsupplying the CNS, single layered leptomeninnx or

leptomeninges.The deeper layer Intima pia closeleptomeninges.The deeper layer Intima pia close

meshwork of fine reticular and elastic fibers adherentmeshwork of fine reticular and elastic fibers adherentto the underlying nervous tissue. Contains branchesto the underlying nervous tissue. Contains branches

of the internal carotid and vertebral artery into theof the internal carotid and vertebral artery into the

substance of CNS.substance of CNS.

Blood brain barrierBlood brain barrier


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Blood brain barrierBlood brain barrier

the close investment of blood capillaries in the CNS bythe close investment of blood capillaries in the CNS by

neuroglial cells and their process.neuroglial cells and their process.

It is now know however, that there is free communicationIt is now know however, that there is free communication

between subarachnoid space and intercellular spacesbetween subarachnoid space and intercellular spaces

allowing passage of macromolecules between cerebrospinalallowing passage of macromolecules between cerebrospinal

fluid and neural tissues.fluid and neural tissues.

It is the result of the occluding junctions between endothelialIt is the result of the occluding junctions between endothelial

cells and brain capillaries.cells and brain capillaries.

Choroid plexus &Choroid plexus &


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CSF:CSF:

Spaces filled with CSF:Spaces filled with CSF:

pia arachnoid spacepia arachnoid space

subarachnoid spacesubarachnoid space = act as water cushion, fills the brain ventricles= act as water cushion, fills the brain ventricles

and the central canal of the spinal cord.0and the central canal of the spinal cord.0

CSF characteristicsCSF characteristics


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CSF characteristicsCSF characteristics

It is a clear colorless liquid, low specific gravity 1.004It is a clear colorless liquid, low specific gravity 1.004to 1.007.to 1.007.

Contents of CSF = potassium, sodium,Contents of CSF = potassium, sodium, chloriodchloriod, some, someglucose and some amount of protein, few lymphocytes.glucose and some amount of protein, few lymphocytes.

Secretions = occurs at the choroid plexus in the roof ofSecretions = occurs at the choroid plexus in the roof ofthe 3rd and 4th ventricle, medial wall of the parts of thethe 3rd and 4th ventricle, medial wall of the parts of thelateral ventricle.lateral ventricle.

Produced at 0.5 liters per day.Produced at 0.5 liters per day.

Cover layer of the choroid plexus is a single layer ofCover layer of the choroid plexus is a single layer ofcolumnarcolumnar ependymalependymal cells with apical. Bulbouscells with apical. Bulbousmicrovillimicrovilli..

CSF pathwayCSF pathway


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CSF pathwayCSF pathway

Choroid plexus, lateral ventricleChoroid plexus, lateral ventricle foramen offoramen of

monroemonroe -->>3rd3rd -->>iteriter--> 4th ventricle> 4th ventricleforaminaforamina

at the roof of the 4th ventricleat the roof of the 4th ventricle -->>

( median foramen of( median foramen of MagendieMagendie, lateral foramina, lateral foramina

ofof LuschkaLuschka subarachnoid spacesubarachnoid space arachnoidarachnoid

villivilli absorbed mainly into the cranial venousabsorbed mainly into the cranial venous

sinusessinuses


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