histologic structure of nervous system
DESCRIPTION
histologic nervous system, neuron, neuroglial, axon, dendrite, brain, spinal cord, blood-brain barrierTRANSCRIPT
HISTOLOGY OF NERVOUS SYSTEM
DR. I WAYAN SUGIRITAMA,M.KesHISTOLOGY DEPARTMENT
MEDICAL FACULTY OF UDAYANA UNIVERSITY
NERVOUS SYSTEMNERVOUS SYSTEM
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The most complex system in the human bodyThe most complex system in the human body Formed by network more than 100 million Formed by network more than 100 million
neuronneuron Each neuron has a thousand Each neuron has a thousand
interconnectioninterconnection a very complex system a very complex system for communicationfor communication
Nerve tissue is distribute throughout the Nerve tissue is distribute throughout the body, anatomically divide into : body, anatomically divide into : CNSCNS & & PNSPNS
Structurally consist : Structurally consist : nerve cells nerve cells & & glial glial cellscells
CONTENTSCONTENTS
Cells of nervous systemCells of nervous system Synaptic communicationSynaptic communication Central nervous system & Peripheral Central nervous system & Peripheral
nervous system & associated nervous system & associated structurestructure
Regeneration of nervous systemRegeneration of nervous system
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REFFERENCESREFFERENCES
Color Textbook Histology, Color Textbook Histology, third edition, leslie P. Gartnerthird edition, leslie P. Gartner
Basic Histology, tenth edition, L. Carlos Basic Histology, tenth edition, L. Carlos Junqueira,2003Junqueira,2003
Histology and Cell Biology, second Histology and Cell Biology, second edition,2007edition,2007
Elsevier’s Integrated Histology,2007Elsevier’s Integrated Histology,2007
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CELLS OF NERVOUS SYSTEM
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NEURON NEUROGLIA
STRUCTURE OF NEURON
Principle cells of Nervous Tissue
Consist of 3 parts : CELL BODY (perikaryon/soma) A single AXON Multiple DENDRITES
ø 5-150 µm
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CELL BODY (PERIKARYON) Central portion of the cell Generally are polygonal Different shape and size
characteristic regions of nervous system
Contain : Nucleus Perinuclear cytoplasm
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ULTRASTRUCTURE OF NEURONNucleus : large, spherical to
ovoid and centraly located
a single prominent nucleolus
finely dispersed chromatin
trancriptionaly active
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ULTRASTRUCTURE OF NEURONCytoplasm :
a. Abundant of R.E.R
b. Polyribosomes
c. Basic dyes (a+b) Nissl Bodies
d. lots of S.E.R.
e. Golgi bodies (perikaryon) protein secreting cell
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ULTRASTRUCTURE OF NEURONCytoplasm
a. Many mitochondria, most abundant in axon terminal
b. extensive cytoskeleton axonal transport
c. One centriole do not undergo cell divisions
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DENDRITE AND AXON AXON
Single process up to 100 cm Originate from axon hillock Devoid ribosome Dilatation of distal portion
axon terminal end bulbs synapse
conducting impulse away from the soma
Axonal transport DENDRITES
Multiple elongated processes Cytoplasmic~perikaryon
(devoid golgi complex) Receiving stimuli 12/04/23 11
NEURONS CLASSIFICATION :According to the size and shape of the processes
(Dorsal root & cranial nerve ganglia)
(Pyramidal & purkinje)
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NEURONS CLASSIFICATION :
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NEURONS CLASSIFICATION :
According to their function : Sensory Neuron (afferent )
Receive sensory input conduct impulses to CNS
Motor Neuron (Efferent) CNS conduct impulses to muscles, glands and other
neurons
Interneuron In the CNS as interconnectors, establish neuronal circuit
between sensory and motor neuron
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NEURON GROUPING
CORTEX Neuron form six layers on the cerrebrum Form three layers on the cerrebellum
NUCLEI In subcortical region (thalamus, midbrain,
brainstem and spinal cord) neuron form irregular cluster nuclei
GANGLION Cluster of neuron outside the CNS
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FUNCTION OF NEURON
Receptive Receptor receive stimuli and tranduce into nerve
impulse and transferro to other neuron Integrative
Processing impulse on the higher center Motor
Initiating motor respons and tranduse impulse to the effector
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SYNAPSES Sites of impulse transmission
Convert electrical signal into chemical signal
Permit neurons to communicate
Types of synapses : Axodentritic synapse Axosomatic synapse Axoaxonic synapse Dendrodentritic synapse
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SYNAPS
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NEUROGLIAL CELLS Metabolic and mechanical
support for neuron 10 times abundant than
neurons Neuroglial cells undergo
mitosis Classification :
Oligodendrocytes Astrocytes Ependymal Cells Microglia Schwan cells
CNS
PNS
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NEUROGLIAL CELLS
Astrocytes Pedicles binds to capillaries
and to the pia mater form glial limitans
Controlling the ionic & chemical environment of neurons
Energy metabolism Form cellular scar tissue Form the blood-brain
barrier
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NEUROGLIAL CELLS
Oligodendrocytes interfascicular
Produce myelin sheath (electrical insulation) in CNS
A single cell wrap several axons (40 to 50)
Form nodes of Ranvier
satellite
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NEUROGLIAL CELLS Schwann cells
Analogue to Oligodendrocyte
Produce myelin sheath in the PNS
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NEUROGLIAL CELLS Microglia Scattered throughout
the CNS Clearing debris Act as APC Protect the CNS from
viruses and microorganism
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NEUROGLIAL CELLS Ependymal Cells
Low columnar ciliated epithelial cells line the ventricles of the brain & central canal spinal cord
Formation of choroid flexus produce CSF
Facilitates the movement of CSF
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Anatomically divided in to :
NERVOUS SYSTEM
CENTRAL NERVOUS SYSTEM (CNS)
PERIPHERAL NERVOUS SYSTEM (PNS)
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THE CNS
Consist of : Cerebrum Cerebellum Spinal cord
No connective tissue soft, gel like
When sectioned : White matter Gray matter
Covered by meninges12/04/23 26
CEREBRUM GRAY MATTER
Contains neuronal cell bodies, dendrites and glial cells
Six layers composed of neuron
Neuron (pyramidal): Afferent (sensory) Efferent (motor)
WHITE MATTER Contains myelinated
axons and myelin-producing oligodendrocytes
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CEREBELLUM
GRAY MATTER Three layers :
Outer molecular layer
Central layer of large Purkinje cells
Inner granule layer WHITE MATTER
The same as cerebrum
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SPINAL CORD
GRAY MATTER (CENTRAL)SHAPE OF “H” Central canal lined by
Ependymal cells Legs of the “H” form :
Anterior horns Posterior horns
Neurons : large and multipolar
WHITE MATTER (PERIPHERAL)
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PNS Bundles of nerve fibers
(axons) outside the CNS & surrounded by connective tissue
Main component : Peripheral nerves Ganglia Nerve endings
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NERVE FIBERS
Consist of axons enveloped by a special sheath
Group of fibers constitute the peripheral nerve
Two types :Myelinated fiberUnmyelinated fiber
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NERVE FIBERS Myelinated fibers A single Schwann cell
wraps around single axon form myelin sheath nodes of Ranvier
Unmyelinated fibers A single Schwann cell
envelopes several axon Fibers enveloped within
simple clefts of Schwann cells
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MYELINATION PROCESS
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CONDUCTION VELOCITYDepend on the extent of
Myelination : Unmyelinated fibers
No nodes of Ranvier continuous conduction
Slower conduction
Myelinated fibers Gap of myelin sheath (nodes
of Ranvier ) saltatory conduction
Faster conduction
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CONNECTIVE TISSUE INVESTMENTS Epineureum
Dense collagenous Con. Tissue with thick elastic fiber
Prevent damage by overstreching
Perineureum Dense con. Tissue Layers of epithelioids Isolates neural environment
(blood-nerve barrier)
Endoneureum Loose con. Tissue Regulation of
microenvironment of nerve fiber
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PERIPHERAL NERVE
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PERIPHERAL NERVE
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GANGLIA
Ovoid structure containing neuronal cell bodies, glial cells supported by connective tissue
Function : Relay stations to transmit impulses Types :
Sensory ganglia Autonomic ganglia
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GANGLIA Sensory Ganglia (cell bodies of
sensory neuron) Unipolar cell bodies enveloped
by cuboidal capsule cells Cranial ganglia : Associated with
the cranial nerve Spinal ganglia : Associated with
the spinal nerve
Autonomic Ganglia (cell bodies of postganglionic autonomic nerves) Multipolar neuron enveloped
by satellite cells Some are located within
certain organ (intramural)
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DORSAL ROOT GANGLIA
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FUNCTIONAL CLASSIFICATION OF NERVES
Sensory nerve fibers Carry sensory input from
the cutaneus/ viscera area to CNS
Motor nerve fibers Originate in the CNS
carry motor impulses to the effector organs
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FUNCTIONAL CLASSIFICATION OF MOTOR COMPONENT
Somatic nervous system Provide motor impulses
to skeletal muscles Cells bodies (multipolar)
originate in the motor nuclei of the brain or ventral horn of spinal cord
The axon travel to the skeletal muscle via cranial or spinal nerve
Autonomic nervous system Provide motor impulses
to the smooth muscle of viscera, cardiac muscle, secretory cells
HOMEOSTASIS
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AUTONOMIC NERVOUS SYSTEMANS = two-neuron network First Neuron
Neuron in CNS Axon (preganglionic
fibers) form a synapse with second multipolar neuron in ganglion
Second Neuron Neuron in the Ganglion Axon to the effectors
(postganglionic fibers)
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AUTONOMIC NERVOUS SYSTEM
SYMPHATETIC SYSTEM The nuclei located in the
thoracic and lumbar segment of spinal cord
Preganglionic fibers leave the CNS by way of ventral roots
The chemical mediator postganglionic fibers is norepinephrine
PARASYMPHATETIC SYSTEM The nuclei located in the
medulla and midbrain and in the sacral portion of spinal cord
Pre ganglionic fibers leave the CNS trough cranial nerve III, VII, IX and X and also trough II, III, IV sacral nerve
The ganglion located near the effector organs
The chemical mediator pre and postganglionic fibers is acethilcholine
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MENINGES The dura mater
dense, collagenous connective tissue
The arachnoid layer: fibroblasts, collagen &
elastic fibers Layer in contact with dura
mater & a system of trabeculae
Form arachnoid villi The pia mater
Loose con. Tissue with blood vessel
There is a physical barrier between pia mater & neuron
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BLOOB-BRAIN BARRIERPrevents the passage of substances (bacterial, toxic, Chemical…) from blood to nerve tissue Endothelial of capillary
Occluding junction No fenestration
Expansions of Astrocytes cell processes that envelope the capillary
↓ permeability
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CHOROID FLEXUS
Choroid flexus consist of loose conn. tissue of the pia matter, covered by a simple/ low columnar epith. ion transporting cells
Elaborate CSF fill the ventricles subarachnoid space (arachnoid villi)venous
CSF function metabolism and protective of CNS
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CEREBROSPINAL FLUID Composition
clear, low density & protein
content High Na, K, Cl
Function Metabolic Liquid cushion
Blood-CSF barrier Zonulae occludents
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NERVE REGENERATION Diseases affecting Schwann cellsloss of
myelin (segmental demylination) Nerve injury induced axonal degeneration
(wallerian degeneration) followed by regeneration
Axon reaction : Local changes Anterograte changes Retrograte changes
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Axon reaction Local reaction
Severe ends of axon retract & cuts membrane fuses Macrophage & fibroblasts infiltration
Anterograde reaction Axon terminal degeneration Schwann cells proliferation form a column of Schwann
(endoneureum is essential for proliferation of Schwann cells)
Retrograde reaction Chromatolysis in perikaryon Several sprouts of axons emerge from proximal stump Axon sprouts enter the schwan tubes and guided to reach the
target organ22/04/2009 50
Axon reaction
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REGENERATION OF CNS ??
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Regeneration nerve fibers in CNS is not possible, because : An endoneureum is not present Oligodendrocytes do not proliferate Astrocytes deposit scar tissue (plaque)
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