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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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CNS NEUROGLIACNS NEUROGLIA
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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CNS NEUROGLIACNS NEUROGLIA
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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CNS NEUROGLIACNS NEUROGLIA
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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NEURON PROCESSESNEURON PROCESSES
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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NEURON PROCESSESNEURON PROCESSES
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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NEURON PROCESSESNEURON PROCESSES
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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NEURON PROCESSESNEURON PROCESSES
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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NEURON PROCESSESNEURON PROCESSES
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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NEURON PROCESSESNEURON PROCESSES
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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NEURON PROCESSESNEURON PROCESSES
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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NEURON PROCESSESNEURON PROCESSES
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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MYELIN SHEATHMYELIN SHEATH
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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MYELIN SHEATHMYELIN SHEATH
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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MYELIN SHEATHMYELIN SHEATH
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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MYELIN SHEATHMYELIN SHEATH
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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NEURON CLASSIFICATIONNEURON CLASSIFICATION
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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NEURON CLASSIFICATIONNEURON CLASSIFICATION
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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Nerve FiberNerve Fiber
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))
Nerve FiberNerve Fiber
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Nerve FiberNerve Fiber
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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TYPES OF CIRCUITSTYPES OF CIRCUITS
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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TYPES OF CIRCUITSTYPES OF CIRCUITS
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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TYPES OF CIRCUITSTYPES OF CIRCUITS
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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TYPES OF CIRCUITSTYPES OF CIRCUITS
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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Thank youThank you