topic 3 (neurons and glia july 2010)

8/3/2019 Topic 3 (Neurons and Glia July 2010)

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NEURONS AND GLIANEURONS AND GLIA


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BIO616BIO616 Neurons and GliaNeurons and Glia 22

LEARNING OBJECTIVESEARNING OBJECTIVESAt the end of this topic students should beAt the end of this topic students should be

able to:able to: discuss the difference between neurons anddiscuss the difference between neurons and

gliaglia discuss the structure of neurons and gliadiscuss the structure of neurons and glia Discuss the different techniques of stainingDiscuss the different techniques of staining

nerve cellsnerve cells discuss the functions of neurons and gliadiscuss the functions of neurons and glia discuss the neuron doctrinediscuss the neuron doctrine classify different types of neuronsclassify different types of neurons


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LEARNING OUTCOMESEARNING OUTCOMESAt the end of this topic students must be able to:At the end of this topic students must be able to: differentiate between different histologicaldifferentiate between different histological

techniques used to differentiate different parts oftechniques used to differentiate different parts ofneuronsneurons

draw and correctly label a typical neurondraw and correctly label a typical neuron state and discuss the functions of neuronsstate and discuss the functions of neurons state and discuss the functions of gliastate and discuss the functions of glia name the different types of glianame the different types of glia

Correctly classify neurons based on structure, neuralCorrectly classify neurons based on structure, neuralconnections, axonal length and types ofconnections, axonal length and types ofneurotransmitterneurotransmitter

Discuss the concept of neural circuits and state atDiscuss the concept of neural circuits and state atleast one example of a neural circuitleast one example of a neural circuit


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IntroductionntroductionNeurophilosophyNeurophilosophy

Brain is the origin of mental abilitiesBrain is the origin of mental abilities

NeuronsNeurons

Process and transmit informationProcess and transmit information

Sense environmental changesSense environmental changes

Communicate changes to other neuronCommunicate changes to other neuron

Command body responseCommand body response


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Introductionntroduction Glial cellsGlial cells (10-50x more of these than

neurons)

Structural support Maintenance of ionic compositions

Remove extrachemicals (neurotransmitters,) followingtheir release from neurons

Insulate neurons electrically

Formation of blood-brain barrier Secretion of compounds for neuronal maintenance

Participate in information flow in the nervous system


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The Neuron Doctrinehe Neuron Doctrine HistologyHistology

Study of tissueStudy of tissue

structurestructure The Nissl StainThe Nissl Stain

Facilitates the studyFacilitates the study

of cytoarchitecture inof cytoarchitecture in

the CNSthe CNS


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The Neuron Doctrinehe Neuron DoctrineNISSLBODIES

NEURONS


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The Neuron Doctrinehe Neuron Doctrine Silver nitrate stainSilver nitrate stain

Stains random neuronsStains random neurons

Discovered by Golgi (1873) inDiscovered by Golgi (1873) in

a kitchen workinga kitchen working bybycandlelightcandlelight


Camillo Golgi (1843-1926)

Purkinje cell(cerebellum)


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The Neuron Doctrinehe Neuron Doctrine Golgi-stain shows twoGolgi-stain shows two

parts of neurons:parts of neurons: Cell body, soma orCell body, soma or

perikaryonperikaryon

Neurites: Axons andNeurites: Axons anddendritesdendrites


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The Neuron Doctrinehe Neuron Doctrine Cell bodyCell body

The expended portion of the neuron that contains nucleusThe expended portion of the neuron that contains nucleus Stains basophilically due to the abundance of RER andStains basophilically due to the abundance of RER and

polyribosomespolyribosomes

The clumps of RER and polyribosomes are referred to asThe clumps of RER and polyribosomes are referred to asNissl BodiesNissl Bodies DendritesDendrites

One to many extensions of the cell bodyOne to many extensions of the cell body Specialized to receive input from other neurons or fromSpecialized to receive input from other neurons or from

receptorsreceptors

Contain Nissl bodies in their proximal parts and thus theContain Nissl bodies in their proximal parts and thus theinitial portions of dendrites stain basophilicallyinitial portions of dendrites stain basophilically

Often have small protrusions, called dendritic spines, thatOften have small protrusions, called dendritic spines, thatexpand the dendritic surface area and serve as sites ofexpand the dendritic surface area and serve as sites ofsynaptic contantsynaptic contant


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The Neuron Doctrinehe Neuron Doctrine Golgi silver stain: neuron from theGolgi silver stain: neuron from the

cerebellumcerebellum

CELL BODYENDRITES


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The Neuron Doctrinehe Neuron Doctrine Neurons: Continuous or contiguous?Neurons: Continuous or contiguous?

Fused neural networks or independent?Fused neural networks or independent?

If fused How can there be localizationIf fused How can there be localizationof function as suggested by Brocasof function as suggested by Brocas

finding?finding?



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The Neuron Doctrinehe Neuron Doctrine Cajals ContributionCajals Contribution

Neural circuitryNeural circuitry

Neurons communicateNeurons communicateby contact, notby contact, not

continuitycontinuity

Neuron doctrineNeuron doctrine Neurons adhere to cellNeurons adhere to cell

theorytheory

Santiago Ramon y Cajal(1852-1934)


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The great debate what units make uphe great debate what units make upthe brain?he brain?Camillo Golgiamil lo Golgi Santiago Ramon y Cajalantiago Ramon y CajalInvented Golgi technique ofInvented Golgi technique of Used the Golgi method on brainUsed the Golgi method on brain tissuetissue

examining brain tissueexamining brain tissue

Argued fervently (and correctly)Argued fervently (and correctly) thatthat

Argued fervently (andArgued fervently (and neurons are single cellsneurons are single cells

incorrectly) that the brainincorrectly) that the brain

is ais a network, or reticulum, ofnetwork, or reticulum, of Guessed correctly at the directionGuessed correctly at the direction

connected cellsconnected cells of information flow within theof information flow within the

nervous system, judging by cellnervous system, judging by cell structurestructure

Discovered the Golgi apparatusDiscovered the Golgi apparatus

and the Golgi stretch receptorand the Golgi stretch receptor Described many cell types inDescribed many cell types in many brainmany brain

structures, including developing neuronsstructures, including developing neurons

Neuron doctrineNeuron doctrine



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The great debate what unitshe great debate what unitsmake up the brain?ake up the brain? The two men disagreed up to theThe two men disagreed up to the

death of Golgi 10 years before Cajaldeath of Golgi 10 years before Cajal

They also shared the Nobel prize inThey also shared the Nobel prize in19061906

BIO616BIO616

Neurons and GliaNeurons and Glia

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BIO616BIO616


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The Prototypical Neuronhe Prototypical Neuron Neuronal membraneNeuronal membrane

The cell body (soma)The cell body (soma) Contains nucleus & organelles common

functions Mainly found in CNS Cytosol: Watery fluid inside the cellCytosol: Watery fluid inside the cell

Organelles: Membrane-enclosed structures withinOrganelles: Membrane-enclosed structures withinthe somathe soma Cytoplasm: Contents within a cell membraneCytoplasm: Contents within a cell membrane

(e.g., organelles, excluding the nucleus)(e.g., organelles, excluding the nucleus)


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BIO616BIO616


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The Prototypical Neuronhe Prototypical Neuron The SomaThe Soma

Gene expressionGene expression

Protein synthesisProtein synthesis

RNA splicingRNA splicing

Molecular biologyMolecular biology


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Rough EndoplasmicRough Endoplasmic

Reticulum (ER)Reticulum (ER) Major site for proteinMajor site for protein

synthesissynthesis

Free ribosomesFree ribosomes

PolyribosomesPolyribosomes


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Rough ERRough ER

Protein synthesis in neuronsProtein synthesis in neurons


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Smooth ER and Golgi ApparatusSmooth ER and Golgi Apparatus

Sites for preparing/sorting proteins forSites for preparing/sorting proteins fordelivery to different cell regions (trafficking)delivery to different cell regions (trafficking)

and regulating substancesand regulating substances


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MitochondrionMitochondrion

Site of cellularSite of cellularrespiration (inhale andrespiration (inhale and

exhale)exhale)

Krebs cycleKrebs cycle

ATP- cells energyATP- cells energysourcesource


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The Prototypical Neuronhe Prototypical Neuron The Neuronal MembraneThe Neuronal Membrane

Barrier that encloses cytoplasmBarrier that encloses cytoplasm

~5 nm thick~5 nm thick

Protein concentration in membrane variesProtein concentration in membrane varies

Structure of discrete membrane regionsStructure of discrete membrane regions

influences neuronal functioninfluences neuronal function


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The Prototypical Neuronhe Prototypical Neuron The CytoskeletonThe Cytoskeleton

Not staticNot static

Internal scaffolding ofInternal scaffolding ofneuronal membraneneuronal membrane

Three bonesThree bones

MicrotubulesMicrotubules MicrofilamentsMicrofilaments

NeurofilamentsNeurofilaments


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The Prototypical Neuronhe Prototypical NeuronAxon

Forms connection with target (effector)

Conducts impulses away from the cellbody Typically one per neuron Lacks Nissl bodies and does not stain with

routine histological stains


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The Prototypical Neuronhe Prototypical Neuron The AxonThe Axon

Axon hillock (beginning)Axon hillock (beginning)

Axon proper (middle)Axon proper (middle)

Axon terminal (end)Axon terminal (end)

Differences betweenDifferences between

axon and somaaxon and soma

ER does not extend intoER does not extend into

axonaxon

Protein composition:Protein composition:

UniqueUnique

I t Z


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Output ZoneAxon

Terminals

Nucleus

Axon

Cell body

Dendrites

Input Zone

Dendrites

and

Cell body

Trigger Zone

Axon hillock

Conducting Zone

Axon (may be from 1mm

to morethan 1 m long

Arrows indicate the

direction in which nervesignals are conveyed.


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The Axon TerminalThe Axon Terminal

Differences between the cytoplasm of axonDifferences between the cytoplasm of axonterminal and axonterminal and axon

No microtubules in terminalNo microtubules in terminal

Presence of synaptic vesiclesPresence of synaptic vesicles

Abundance of membrane proteinsAbundance of membrane proteins Large number of mitochondriaLarge number of mitochondria


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SynapseSynapse

Gap between a synapticGap between a synapticterminal and target cellterminal and target cell Synaptic transmissionSynaptic transmission Electrical-to-chemical-to-Electrical-to-chemical-to-

electrical transformationelectrical transformation Synaptic transmissionSynaptic transmission

dysfunctiondysfunction Mental disordersMental disorders


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Axoplasmic transportAxoplasmic transport

Anterograde (soma to terminal) vs.Anterograde (soma to terminal) vs.

Retrograde (terminal to soma) transportRetrograde (terminal to soma) transport


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The Prototypical Neuronhe Prototypical Neuron DendritesDendrites

Where incoming fibres make connectionsWhere incoming fibres make connections

Conveys signals to the cell bodyConveys signals to the cell bodyAntennae of neuronsAntennae of neurons

Dendritic treeDendritic tree

Synapse - receptorsSynapse - receptors Dendritic spinesDendritic spines

Postsynaptic (receives signals from axonPostsynaptic (receives signals from axon

terminal)terminal)


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The Prototypical Neuronhe Prototypical Neuron

DENDRITICSPINES


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Classifying Neuronslassifying Neurons A single neuron

on the surfaceof a

microprocessor A cm3 of the

human brain willcontain morethan 50 millionneurons.


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Classifying Neuronslassifying Neurons Structural (Anatomical)Structural (Anatomical)

Classification Based on theClassification Based on theNumber of Neurites (Processes)Number of Neurites (Processes) Unipolar (Psuedounipolar)Unipolar (Psuedounipolar)

Has one neurite thatbifurcates The cell body of this neuronal

type is found in spinal andcranial ganglia

BipolarBipolar Has 2 neurites (relatively rare;

retina of eye and certain cranialganglia)

MultipolarMultipolar Many neurites; typically 1 axon

and 2 or more dendrites (mostcommon type of neuron)


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Classifying Neuronslassifying Neurons Structural ClassificationStructural Classification

Based on Dendritic andBased on Dendritic and

Somatic MorphologiesSomatic Morphologies Stellate cells (star-Stellate cells (star-

shaped) and pyramidalshaped) and pyramidal

cells (pyramid-shaped)cells (pyramid-shaped)

Spiny or aspinousSpiny or aspinous


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Classifying Neuronslassifying Neurons Some lack dendritesSome lack dendrites

altogetheraltogether

Some showSome showdendriticdendritic

arborizations (tree-arborizations (tree-

like arrangement)like arrangement)


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Classifying Neuronslassifying Neurons

FunctionallyFunctionally Motor (Efferent) Related to innervation of muscle, glands

etc. Activation ofthese neurons leads to some

motor event (i.e., contraction of amuscle)

Sensory (Afferent) Related to the transfer of sensory

information (i.e., pain touch, pressure,etc.)

Most synapse with interneurons e.g., neurons of spinal (dorsal root)

ganglia Interneurons

Neither motor or sensory (e.g., neuronsresponsible for the various spinalreflexes)

Synapse only with other neurons


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Comparison of Structuralomparison of StructuralClasses of Neuronslasses of Neurons


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Structuralructural D iversity ofversity ofNeuronsurons


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Classifying Neuronslassifying Neurons Further ClassificationFurther Classification

Based on axonal lengthBased on axonal length

Golgi Type IGolgi Type I Golgi Type IIGolgi Type II

Based on neurotransmitter typeBased on neurotransmitter type e.g., Cholinergic = Acetycholine at synapsese.g., Cholinergic = Acetycholine at synapses

Adrenergic = Adrenaline at synapsesAdrenergic = Adrenaline at synapses


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Simple circuitSimple circuit

Synapse between sensory neurons & motorSynapse between sensory neurons & motor

neurons, resulting in a simpleneurons, resulting in a simple reflexeflex Complex circuitComplex circuit

Such as those associated with most behaviors,Such as those associated with most behaviors,

involve integration by interneurons in the CNSinvolve integration by interneurons in the CNS

Convergent circuitsConvergent circuits Divergent circuitsDivergent circuits

Reverberating circuits (memory storage)Reverberating circuits (memory storage)

Neural Circuitseural Circuits


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Neural Circuitseural Circuits The myotaticThe myotatic

(knee-jerk) spinal(knee-jerk) spinal

reflexreflex

The synapticThe synapticconnections betweenconnections between

thethe sensorysensoryafferentsafferentsand the extensorand the extensor

efferentsefferents areare

excitatoryexcitatory

TheThe interneuronsinterneuronsactivated by theactivated by the

afferentsafferents areare

inhibitoryinhibitory

http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2855http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2855http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2263http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2263http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2435http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2435http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2556http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2556http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2263http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2263http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2263http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2556http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2435http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2263http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2855


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Neural Circuitseural Circuits Action potentialAction potential activity measured from each element (activity measured from each element (

afferentsafferents,, efferentsefferents, and, and interneuronsinterneurons) before, during,) before, during,

and after a stimulusand after a stimulus

http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2254http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2254http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2263http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2263http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2435http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2435http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2556http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2556http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2556http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2435http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2263http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2254


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Neural Circuitseural Circuits Intracellular recording ofIntracellular recording of

the potential changesthe potential changes

underlying the synapticunderlying the synaptic

connections of theconnections of themyotaticmyotatic reflexreflex circuitcircuit

http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2819http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2819http://www.ncbi.nlm.nih.gov/bookshelf/?book=neurosci&part=A2251&rendertype=def-item&id=A2819


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Neural Circuitseural Circuits The three functional classes of neurons are theThe three functional classes of neurons are the

basic constituents of all neural circuitsbasic constituents of all neural circuits After birth, neurons grow, and their connectionsAfter birth, neurons grow, and their connections

are enrichedare enriched Neurons are organized in different ways inNeurons are organized in different ways in

different parts of the NSdifferent parts of the NS The density of cells of different types varies asThe density of cells of different types varies as

wellwell Neural projections, example, the dendrites ofNeural projections, example, the dendrites of

neurons, are enriched through experienceneurons, are enriched through experience


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Neural Circuitseural CircuitsExperiment:Experiment:

Rats from the same litter are divided intoRats from the same litter are divided into

two setstwo setsRat A is placed in regular lab box that isRat A is placed in regular lab box that isclean but otherwise boringclean but otherwise boring

Rat B, is put in a nice cage with toysRat B, is put in a nice cage with toys

After 6 months, the animals are sacrificed,After 6 months, the animals are sacrificed,and their brains studiedand their brains studied


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Neural Circuitseural CircuitsResults:Results:

Rat A, has fewer glial cells than does rat BRat A, has fewer glial cells than does rat B

The neurons in rat A have fewer projections thanThe neurons in rat A have fewer projections thanrat B does: the neurons are not as rich inrat B does: the neurons are not as rich in

projection to other neuronsprojection to other neurons

This demonstrates how experience andThis demonstrates how experience and

interaction with the environment enhance neuralinteraction with the environment enhance neural

developmentdevelopment


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Coordination by clusteroordination by cluster Nerve cell bodies are often arranged intoNerve cell bodies are often arranged into

clustersclusters

Allow coordination of activities by only a part of theAllow coordination of activities by only a part of the

nervous systemnervous system

A nucleuA nucleuss is a cluster of nerve cell bodiesis a cluster of nerve cell bodieswithin the CNS (accumulation of grey matter)within the CNS (accumulation of grey matter)

A ganglion is a cluster of nerve cell bodies inA ganglion is a cluster of nerve cell bodies inthe PNSthe PNS


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Coordination by clusteroordination by cluster

Ganglion cells inthe PNS

Dorsal

RootGanglia


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Coordination by clusteroordination by cluster

Brain nuclei

Brainnuclei


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Supporting cellsupporting cells Do not conduct impulsesDo not conduct impulses Outnumber neurons by 10- 50-Outnumber neurons by 10- 50-

foldfold Neurons in CNSNeurons in CNS

Terminally differentiatedTerminally differentiated Incapable of divisionIncapable of division

Glial cells Certain subtypes possess ability to

divide Of interest in terms of understanding

this ability applicable to neurons?Ability to divide most CNS (brain)

tumors linked to glial cells

50

m

Astrocytes


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Supporting cellsupporting cells The CNS has three types and the PNS

has one Neuroglia in the CNS

AstrocytesAstrocytes

Star-shaped cells that play an active role inbrain function by influencing the activity ofneurons

Clearing and recycling of neurotransmitters Clean up brain debris Transport nutrients (neurotrophins e.g.

neural growth factor) to neurons Hold neurons in place Digest parts of dead neurons Regulate content of extracellular space Contribute to formation of blood brain barrier


Astrocyte labeled with anti-GFAP antibody

GFAP: glial cell fibrillary acidicprotein

Neuron growing on an astrocyticneuroglia cell


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Supporting cellsupporting cells Fibrous astrocytesFibrous astrocytes

Prevalent in white matterPrevalent in white matter

Higly filamentousHigly filamentous Protoplasmic astrocytesProtoplasmic astrocytes

Abundant in grey matterAbundant in grey matter

Less filamentousLess filamentous

http://upload.wikimedia.org/wikipedia/en/c/cd/Gfapastr5.jpg


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Supporting cellsupporting cells Neuroglia in the CNS

OligodendrocytesOligodendrocytes The analogue of the Schwann cell in the central

nervous system Form the myelin sheaths that insulate the CNS nerveForm the myelin sheaths that insulate the CNS nerve

processesprocesses


Stained for galactocerbroside


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Supporting cellsupporting cells Neuroglia in the CNS

MicrogliaMicroglia The smallest of glial cells

Involved in immune responseInvolved in immune responsein CNSin CNS Help clean up debris/dyingHelp clean up debris/dying

cellscells Probably a distinct lineage ofProbably a distinct lineage of

cells from other gliacells from other glia

May be linked to destructionMay be linked to destruction

of myelin-producingof myelin-producing

oligodendrocytesin certainoligodendrocytesin certain

forms of multiple sclerosisforms of multiple sclerosisBIO616BIO616 Neurons and GliaNeurons and Glia 5454

Microglialcells (yellow) ingestbranched oligodendrocytecells(purple) ---the process thought to

occur in multiple sclerosis


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Supporting cellsupporting cells Supporting cells inSupporting cells in

the CNSthe CNS

Ependymal cellsEpendymal cells Epithelial-like cellsthat line the surfacesof the brain(ventricles and thecentral canal of thespinal cord)

form barriersform barriers

betweenbetween

compartments (BBB)compartments (BBB)

Ependymalcells


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Supportingupportingcellsel ls

Supporting cells in the CNSSupporting cells in the CNS

Radial gliaRadial glia

Important during developmentImportant during developmentof the CNSof the CNS

Provide pathways for neuronalProvide pathways for neuronal

growth and targetinggrowth and targeting

In adult: Mller cells (retina);In adult: Mller cells (retina);Bergmann cells (cerebellum) areBergmann cells (cerebellum) are

derived from radial gliaderived from radial glia


DiI fill of an individual radial gliacell (red) inthe mouse embryonic olfactory bulbcounterstained for tissue architecture (green)
http://en.wikipedia.org/wiki/File:Cultured_schwann_cell.jpg


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Supportingupportingcellsel ls Neuroglia in the PNS

Lemmocytes(Schwann cells)Schwann cells) Form the insulating myelinForm the insulating myelin

sheath around axons in thesheath around axons in thePNS (wrap individually aroundPNS (wrap individually around

the shaft of peripheral axons)the shaft of peripheral axons) Composed primarily of lipids The lipid serves as an insulator

thereby speeding thetransmission rate of actionpotentials along the axon

Analogous to oligodendrocytesAnalogous to oligodendrocytes Surround other axons w/oSurround other axons w/oforming myelinforming myelin


A Schwann cell inculture

electron micrograph showing a Schwanncell (G) surrounding an axonal process (A)
http://en.wikipedia.org/wiki/File:Cultured_schwann_cell.jpg


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Supporting cellsupporting cells Myelination of neuronsMyelination of neurons

Occurs when Schwann cells or oligodenrocytes grow around anOccurs when Schwann cells or oligodenrocytes grow around an

axon so their plasma membranes form concentric layersaxon so their plasma membranes form concentric layers

In MS, myelin sheaths deteriorate causing a disruption of nerveIn MS, myelin sheaths deteriorate causing a disruption of nerve

impulse transmission & consequent loss of coordinationimpulse transmission & consequent loss of coordination


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Supporting cellsupporting cells Myelination of neuronsMyelination of neurons


Oligodendrocyte

Oligo processes forming myelinsheaths on CNS axons

Axon


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Supporting cellsupporting cells Neuroglia in the PNS

Sattelite cells

Important for structure ofImportant for structure ofperipheral nervous systemperipheral nervous system

support cellsupport cell

Common in gangliaCommon in ganglia

May contribute toMay contribute toinsulation of neuroninsulation of neuron


This type I neuron is ensheathedby processesfrom a satellite glialcell (S), which forms a thinmyelin sheath. On the right is the axon hillock.


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Supporting cellsupporting cells

Neuron

Astrocytes

Oligodendrocytes


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Oligodendrocytes

Astrocytes


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Supporting cellsupporting cellsPNS: Glia =Lemmocyte

Nerve fibres

Lemmocyte


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Summaryummary

Structuralcharacteristics of a

neuron tell us about

its function

NEURONS

Soma

AxonsDendrites

Synapse

Elaborate

structure of

dendritic tree =

receiver

e.g., Dense Nissl

stain = protein;

suggests

specialization

Structure Correlateswith Function

topic 3 (neurons and glia july 2010)

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