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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