This document discusses the structure and function of nervous tissue. It begins by defining the basic components of nervous tissue: neurons, nerve processes (axons and dendrites), and neuroglia. It then describes in detail the anatomy and roles of neurons, glial cells like astrocytes and oligodendrocytes, myelination of axons, and synaptic transmission of nerve impulses between neurons. In summary, it provides an overview of the key cell types in the nervous system and how they enable neural signaling and communication.

1. Nervous Tissue
DR. DEVI
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16-4-19

2. Contents
• Neuron
• Nerve cell processes
• Synapses And impulse
transmission
• The neuroglia
• Myelin sheath
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3. The Neuron
• Special property of irritability & conductivity
• Nerve cells are capable of receiving the information from
external and internal environment (Pain, touch, temperature,
pressure)
• This information is relayed to CNS by nerve cell processes
• CNS integrates and interprets this information and commands
are distributed to effector tissue via nerve cells
• information is also stored in the brain for future reference in
the form of memory
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4. Nervous tissue composed of :
• Nerve cell ( Neuron)
• Nerve cell processes
• Neuroglia
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5. THE NEURON
• Functional cell unit of nervous tissue
• Highly specialized to carry information in the
form of electric signals from one cell to another
• Cell body & nerve cell process
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6. Nerve cell body
• Typical pale staining euchromatic nucleus
with prominent dark nucleolus
• Cytoplasm contain prominent basophilic
material celled – Nissl bodies
• It is an aggregation of RER and free
ribosomes
• Cell body contains all other organelles
• cytoskeleton formed by microtubules
and microfilaments
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7. 7• Neurons in old age may
show presence of
lipofuscin pigment
(neuronal lysosomes)
• Size 10um- 120um
• Neurons don’t divide
after birth hence, their
number doesn’t increase
during life time

8. Nerve cell processes
• Elongated cytoplasmic processes take origin from the
cell body
• These process may travel long distances from neuron
• Two types of nerve cell processes - single axon &
multiple dendrites
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9. Dendrites
• Short, multiple
• Each of these may branch extensively to form “
dendritic tree”
• They are involved in receiving information from other
cells – input portions of neuron
• Cytoplasm of dendrites contains Nissl bodies,
microtubules, microfilaments and other organelles
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10. Axon
• Nerve cell processes that send information in the form of
electrical signals away from nerve cell body to another
• Usually one axon for each cell body
• Originate from a conical region – Axon hillock
• End in terminal branching pattern
• Axolemma
• Axoplasm
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11. • Axoplasm contains neurofilament and microtubules , but
lack Nissl bodies and Golgi apparatus
• Nissl substance is also absent from the region of axon
hillock
• Axons are surrounded by myelin sheath
• Axonal transport system
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12. Differences between axon and dendrites
Axon
• Single ,long, thin process
• Terminates away from cell
body
• Rarely branches
• Uniform diameter
• Smooth surface
• Free of nissl bodies
• Nerve impulse travel away
from the cell body
Dendrites
• Multiple, short, thick ,tapering
process
• Terminate near cell body
• Highly branching
• Dendritic tree
• Thickness reduces as it divides
• Surface not smooth
• Contain Nissl bodies
• Nerve impulse travel towards
CB
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13. The Neuroglia
• CNS contains no connective tissue component
• smeller
• Supporting cells
• Function : fill-up the space, provide support,
ensheathment , facilitates during nerve transmission
• 5-50 times more than neurons
• Cannot generate impulses
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14. 14• Neuroglial cells of PNS:
1. Schwann cells
2. Satellite cells
• Neuroglial cells of CNS:
1. Ependymal cells
2. Astrocytes
3. Oligodendrocytes
4. Microglia

15. Ependymal cells
• Arranged in a single layer
• Ciliated columnar or cuboidal cells
• Line the ventricles of brain and central canal of
spinal cord
• Function : responsible for the formation of CSF
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16. Astrocytes
• Star shaped,
• Protoplasmic astrocyte- abundant cytoplasm
present, found in grey matter, end-feet/
vascular feet
• Fibrous astrocytes- long , fewer in number,
found in white matter
• Functions : help in providing nutrients to
neurons, formation of blood-brain barrier,
maintaining chemical environment for
generation of impulse, metabolism of
neurotransmitter , migration of neurons at
the time of brain development
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17. Oligodendrocytes 17
• Small round or oval cells
• Few cytoplasmic process
• Found in CNS
• Functions; produce myelin sheath
around axons in CNS, form
supportive network around CNS
neurons

18. Microglia
• Involved in phagocytic activity
within CNS, can engulf invading
microorganisms
• Rarely found
• Small cells with tortuous process
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19. Schwann cells
• Flattened cells with flattened
nucleus surrounded by abundant
cytoplasm
• Present in PNS only
• Functions : produce myelin
sheath, participate in regulation
of PNS axon
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20. 20

21. Satellite cells
• Surround the nerve cells of ganglia
• flattened cells
• Prominent nuclei
• Present in PNS
• Functions: insulates and support
neurons of ganglia, also provide
pathways for metabolic exchange
•
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22. Classification of Neurons
• Functionally, three types: sensory, motor, interneuron
• Classified on the basis of the shape of the cell body,
which is depending on the number and orientation of cell
process arising from it
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23. 23
• Unipolar – only one process present, found in mesencephalic nucleus of
trigeminal nerve
• Pseudounipolar neurons –one process that extends from cell body and
bifurcates forming a T- shape, one branch extends to CNS and other to
PNS , found in dorsal root ganglion & cranial nerve ganglia

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• Bipolar neurons : they have two process , found in retina &
ganglion of VII CN
• Multipolar neurons- have only one axon, many dendrites
(satellite/star like) or pyramidal/triangular , most common type,
found in spinal cord , cerebrum, cerebellum; motor neurons and
interneurons

25. Synapse
• Specialized region of contact between two
neurons
• At the synapse nerve impulse is
transmitted from one neuron to other
• Transmission of impulse is mediated
through the release of chemical
substances at the synapse
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26. • Presynaptic neuron
• Postsynaptic neuron
• Types of synapses :
1. Axodendritic
2. Axosomatic
3. Axoaxomic
4. Dendrodendritic
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27. Structure of a Synapse
• Axodendritic –most common
• Parts- presynaptic part, synaptic cleft,
postsynaptic part
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28. 28
Presynaptic part -Contains
mitochondria and thickened
cytolemma. Axon terminal
contains many presynaptic
vesicles containing
neurotransmitters
Synaptic cleft- 20-5-um
space, filled with interstitial
fluid. Post synaptic part of
the synapse consist of
thickened region on the
dendrite of the postsynaptic
neuron

29. Impulse transmission
• Neurotransmitter diffuses across synaptic cleft
• Acts on plasma membrane of postsynaptic neuron to
produce postsynaptic potential
• Presynaptic electrical signal -> chemical signal-> electrical
signal
• Chemical synapse, Electrical synapse
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30. Myelin sheath
• Insulating sheath surrounding axons of central peripheral
nervous system
• In PNS Schwann cells form myelin sheath around axons
• In CNS the Oligodendrocytes form myelin sheath around
axons
• Neurolemmal sheath/ Schwann cell sheath
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31. Nodes of Ranvier
• Along the given axon, myelin is formed in discrete units each
unit being formed by one glial cell.
• Between adjacent segments of myelin along each axon a gap
occurs, where axon is not covered by myelin, these gap are
called nodes of Ranvier
• The segment of myelin between two nodes is called inter-
node, which is produced by single Schwann cell
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Nodes of
Ranvier

32. Clinical applications
• Tumors of glial cells: glial cells capable of cell
division , may produce tumors
• Gliomas: tumors of the glial cells of CNS
• Schwannoma: tumors of the Schwann cells
• Medulloblastoma
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33. • Demyelination : degenerative process that erodes away
the myelin sheath that normally protects nerve fibers , it
exposes the nerve fibers and cause problems with nerve
impulse conduction that may affect physical systems
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34. “
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