Download Nervous-histology

THE NERVOUS SYSTEM
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The nervous system is formed of two parts :
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Central Nervous System (CNS)
◦ Includes Brain and Spinal cord
Peripheral Nervous System (PNS)
◦ Includes Cranial nerves ; Spinal nerves and
ganglia .
PNS further subdivided into:
Sensory division (input) and Motor division
(output)
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• Sensory Function
• Sensory receptors gather
information
• Information is carried to the
CNS
• Integrative Function
• Sensory information used to
create:
• Sensations
• Memory
• Thoughts
• Decisions
• Motor Function
• Decisions are
acted upon
• Impulses are
carried to effectors
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Central nervous system
Nerve cells
(neurons)
Gilal cells
(neuroglia)
Conduct
electrical
impulses
Supports and
protect
neurons
-Nerve fibers
- Nerve cells, only
in ganglia.
Supported by connective
tissue
Sensory neurons
Motor neurons
Association neurons
(interneurons)
Neuroglia
Nerve cells

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It is the structural and functional unit of the
nervous tissue.
Consists of the nerve cell body and its
processes.
Processes are formed of
dendrites
axon
Neuron
structure
Cell body
Cell
processes
Dendrites
Axon
Nucleus:
 large,
 spherical
vesicular with a
prominent nucleolus.
 Central in most
neurons,

The cell body contains
the usual organelles
except the centrioles.
why? (not divide)

Nissl bodies: rER + free
ribosomes & polysomes
(protein and membrane
making).
Golgi apparatus:
around the nucleus,
And function to
Synthesize
neuro-transmitters.
 Mitochondria: cellular
respiration.
 Lysosomes: contain
hydrolytic enzymes.
 Lipofuscin: pigment that
accumulate with age.

contains:
 Neurofilaments: intermediate filaments
support.
 Neurotubule:
1. maintains shape
2. intracellular transport mechanism.
Denderites
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Multiple
Short, irregular, wide
base and tapering ends
Gives extensive branches
arise at acute angle.
Cytoplasm contains all
structures as the cell
body except: no Golgi.
Carries impulses towards
cell body; centripetal
Non-myelinated.
Axon
Single
 Long, thin of uniform
diameter.
 Branches at terminal end
may give collateral arise at
right angle.
 Axoplasm lacks Nissl
granules and Golgi
complex.
 Carries impulses away
from cell body; centrifugal
 May be myelinated.

Oligodentrocytes
Schwan cells
Astrocytes
Ependymal cells
Microglia cells
1) Schwann Cells
• Produce myelin found on peripheral myelinated
axons .
• Speed up neurotransmission
2) Satellite Cells
• Support clusters of neuron cell bodies in ganglia .
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1) Microglia
• Phagocytic cell
3) Oligodendrocytes
•Responsible for Myelinaion
In the CNS
2) Astrocytes
•aid in metabolism of
certain substances
• form blood-brain
barrier.
•Supportive in function.
4) Ependyma or ependymal
• Ciliated
• Line central canal of
spinal cord
• Line ventricles of brain
• help regulate composition
of CSF

Formed in peripheral
nervous system ( PNS )
by Schwann cells

Oligodendrocytes form
the myelin sheaths
around the fibers in the
central nervous system
(CNS ) .
Lining the ventricle found in Brain and .
spinal cord , in some places are ciliated to
move the cerebrospinal fluid.
Short elongated cells with short irregular
process (elongated nucleus ). The other have
spherical nucleus .

CNS
Spinal cord
Cerebrum
Brain
Cerebellum
Myelinated axons , Myelin- 
producing oligodendrocytes
Not contain neuronal 
cell bodies , 
Present in central region 
Nuclei (aggregates of 
neuronal cell bodies forming
islands of gray matter
embedded in white matter )
White matter
Neuronal cell bodies
, dendrites and the
initial unmyelinated
portion of the axons
and glial cells
Found at the surface
of the cerebrum and
cerebellum forming
cerebral and
cerebellar cortex.
Gray matter
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
Has 6 layers of cells
with different forms
and sizes.
Some neuron are 
afferent (sensory) ,
other are efferent
(motor).

Has 3 layers ;

1) outer molecular layer ; less cell
dense layer
2) central layer (Purkinje cells) 
;which have spicuous cell body
and long dendrites reach to
molecular layer .
3) inner(granular) layer ; formed 
by very small neurons (smallest
one in the body) , compactly
disposed.

White matter is peripheral. 
Gray matter is central (H shape). 
In horizontal part of H open a 
central canal lined with
Ependymal cells
The legs of H forming anterior 
horns , which contain motor
neuron make up ventral root ,
the gray matter also form
posterior horns , which receive
sensory fibers make up dorsal
root .

Membranous connective tissue
Dura mater 
Arachnoid 
Pia mater 

External layer 
Composed of dense connective tissue 
continuous with periosteum of the skull.
Epidural space contains thin walwd vein , 
loose CT and adipose tissue
Separted from arachnoid by subdural space .
Its internal surface lined with simple squam.
Epith.


Has 2 components; 
Layer in contact with dura mater and system
of trabeculae connecting to pia mater , the
cavities between the trabeculae form
subarachnoid space.

Loose connective tissue

Highly selective permeability barrier that separates the circulating 
blood from the brain extracellular fluid in the central nervous
system.
Formed by brain endothelial cells, which are connected by tight 
junctions with an extremely high electrical resistivity .
allows the passage of water, some gases, and lipid-soluble 
molecules by passive diffusion, as well as the selective transport of
molecules such as glucose and amino acids that are crucial to neural
function. On the other hand, the blood–brain barrier may prevent the
entry of lipophilic, potential neurotoxins by way of an active
transport mechanism mediated by P-glycoprotein. Astrocytes are
necessary to create the blood–brain barrier. A small number of
regions in the brain, including the circumventricular organs (CVOs),
do not have a blood–brain barrier.


Is a collection of nerve cells and fibers
surrounded by a connective tissue capsule
outside the CNS.
There are two types of ganglia.
Autonomic
Sensory (Spinal )
Sympathetic
parasympathetic
Sensory (Spinal)
Autonomic (Symp. & para. )
Two types:
*sympathetic.
*parasympathetic.
 Motor.
 Thin capsule.
 Nerve cells:
* multipolar
* Few
* Small and equal in
diameter.
* Scattered throughout the
ganglion
* Nucleus is eccentric.
* Capsule of satellites is
incomplete.

Sensory.
 Thick capsule.
 Nerve cells:
*unipolar
* many
* Variable in size (20-120µ)
* Grouped
* Nucleus large and central
* Surrounded by complete
capsule of satellite cells

Sensory (Spinal)
Nerve fibers:
* thick & myelinated
* widely separated from
each other.

Autonomic (Sympathetic )
Nerve Fibers:
* Thin & non myelinated
* Close to each other.

Sympatatic & parasympatatic
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A: Normal nerve fiber, with its perikaryon and effector cell (striated
skeletal muscle). Note the position of the neuron nucleus and the
quantity and distribution of Nissl bodies.
B: When the fiber is injured, the neuronal nucleus moves to the cell
periphery, and Nissl bodies become greatly reduced in number. The
nerve fiber distal to the injury degenerates along with its myelin
sheath. Debris is phagocytosed by macrophages.
C: The muscle fiber shows a pronounced denervation atrophy. 
Schwann cells proliferate, forming a compact cord penetrated by the
growing axon. The axon grows at the rate of 0.5—3 mm/day.
D: Here, the nerve fiber regeneration was successful. Note that the
muscle fiber was also regenerated after receiving nerve stimuli.
E: When the axon does not penetrate the cord of Schwann cells , its
growth is not organized. 
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