HISTOLOGY OF NERVOUS
SYSTEM
Nervous System
• The most complex system in the human body.
• Formed by network more than 100 million neuron.
• Each neuron has a thousand interconnection  a very
complex system for communication.
• Nerve tissue is distribute throughout the body,
anatomically divide into : CNS & PNS.
• Structurally consist : nerve cells & glial cells
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Cells of Nervous System
NEURON
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NEUROGLIA
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Structure of Neuron
• Principle cells of Nervous Tissue.
• Consist of 3 parts :
• CELL BODY (perikaryon/soma)
• A single AXON
• Multiple DENDRITES
• 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 Neuron
Nucleus :
• large, spherical to ovoid
and centraly located.
• a single prominent
nucleolus.
• Finely dispersed
chromatin.
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Ultrastructure of Neuron
Cytoplasm:
• Abundant of R.E.R
• Polyribosomes
• Basic dyes (a+b) Nissl
Bodies
• lots of S.E.R.
• Golgi bodies (perikaryon)
 protein secreting cell
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Ultrastructure of Neuron
• Many mitochondria,
most abundant in axon
terminal
• Extensive cytoskeleton
 axonal transport
• One centriole  do not
undergo cell divisions
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Dendrite and Axon
• Axon:
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•
•
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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
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Neurons Classification
According to the size and shape of the processes:
• Multipolar: the most abundant, Ex: pyramidal cells,
Purkinje cells.
• Bipolar: Ex: visual, auditory system.
• Pseudounipolar: Ex: sensoryganglia.
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Neurons Classification
According to the size and shape of the processes
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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 cerebrum.
• Form three layers on the cerebellum.
• 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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Synapses
• Sites of impulse transmission.
• Convert electrical signal into
chemical signal
• Permit neurons to communicate.
• Types of synapses :
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Axodentritic synapse.
Axosomatic synapse.
Axoaxonic synapse.
Dendrodentritic synapse.
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Synapses
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Neuroglial Cells
• Metabolic and mechanical support for
neuron.
• 10 times abundant than neurons.
• Neuroglial cells undergo mitosis.
• Function: provide neurons with structural
support and maintain local conditions for
neuronal function.
• Staining: silver or gold impregnation,
histochemical technique.
• 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
• Protoplasmic astrocytes:
• Granular cytoplasm.
• Envelop the surface of nerve cells and blood vessels.
• Fibrous astrocytes:
• Long processes.
• Predominantly in white matter.
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Neuroglial Cells
• Oligodendrocytes:
• Produce myelin sheath.
(electrical insulation) in
CNS.
• A single cell wrap several
axons (40 to 50).
• Form nodes of Ranvier
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Neuroglial Cells
• Microglia:
• Phagocytic cells, scattered throughout the CNS.
• Derived from mesoderm.
• Small cell bodies.
• Their nuclei have elongated shape.
• Short processes with small expansions –thorny appearance.
• Functions: 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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Neuroglial Cells
• Schwann cells:
• Analogue to
Oligodendrocyte.
• Produce myelin sheath in
the PNS.
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Nervous System is anatomically
divided in to:
• 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 meninges
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Cerebrum
• Gray Matter:
• Contains neuronal cell
bodies, dendrites and glial
cells
• Six layers composed of
neuron
• 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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The 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 fiber
• Unmyelinated 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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Conduction Velocity
Depend 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
• Isolates neural environment
(blood-nerve barrier)
• Endoneureum:
• Loose con. Tissue
• Regulation of
microenvironment of nerve
fiber
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Peripheral Nerve (H&E)
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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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Autonomic Nervous System
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Autonomic Nervous System
Sympathetic System
Parasympathetic 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.
• 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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Regeneration of CNS??
• 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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THANK YOU 
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