Transcript Nervous Tissue 113

NERVOUS TISSUE

Forms the nervous system which is
divided into:
– Central Nervous System (CNS):
» Brain
» Spinal cord
– Peripheral Nervous System (PNS):
» Cranial nerves
» Spinal nerves
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
Neurons (nerve cells): The units of
nervous tissue. They receive and
transmit impulses.
Neuroglial cells: do not receive or
transmit impulses; instead, they
support neurons.
NEURONS
The units of nervous
tissue. They receive and
transmit nerve impulses
to & from the CNS.
 A neuron = nerve cell
body + all its processes:

– One axon.
– One or more dendrites.
Types of Neurons
Unipolar.
 Bipolar.
 Multipolar.

Unipolar Neurons
Formerly called
pseudounipolar.
 Only one process that
divides into a
peripheral branch
(dendrite) and a
central branch (axon).
 Present in the dorsal
root ganglia of spinal
nerves.

Bipolar Neurons
Two processes:
a single
dendrite and a
single axon.
 Present in:

– Nasal cavity
(olfactory
epithelium).
– Inner ear.
– Retina.
Multipolar Neurons
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The most common type.
Multiple dendrites and a
single axon.
Present throughout the
nervous system: e.g.
– Stellate cells: motor
neurons in spinal cord.
– Pyramidal cells: in
cerebral cortex.
– Purkinje cells: in
cerebellum.
Nerve Cell Body

Nucleus: spherical,
central with prominent
nucleolus.

Cytoplasm:
– Abundant rER &
polyribosomes.
– Prominent Golgi.
– Many mitochondria.
– Only 1 centriole.
– Microtubules,
neurofilaments.
Nissl
bodies
Nerve Cell Processes
Dendrites
Axon
One or more processes.
Single thin long process.
Wide base, tapering tip.
Same diameter in any of its parts.
Give many branches.
Few collateral branches.
Ends by terminal arborizations.
Contain mitochondria,
neurofilaments and Nissl bodies.
Contains mitochondria,
neurofilaments but no Nissl bodies.
Carry impulse toward cell body.
Carry impulse away from cell body.
Nerve Fibers
A nerve fiber = any long process of a nerve
cell (axon or dendrite).
 Types of nerve fibers:

– Myelinated:
» Covered by myelin sheath formed by Schwann cells
in PNS and oligodendrocytes in CNS.
» In white matter of CNS and all peripheral nerves.
– Unmyelinated:
» Not covered by myelin sheath.
» In grey matter of CNS and terminal parts of all
peripheral nerve fibers.
Peripheral Nerve Trunk
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The whole nerve is
covered by a C.T.
covering, the
epineurium.
Consists of parallel
myelinated nerve fibers,
arranged in bundles,
separated by C.T.
septa, the perineurium.
The individual nerve
fibers are separated by
C.T., endoneurium.
Epineurium
Perineurium
Endoneurium
NEUROGLIAL CELLS
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Supportive and protective to
neurons. They do not receive
or transmit nerve impulses.
All are present in CNS except
Schwann cell (in PNS).
Types:
– Astrocytes: nutritive function.
– Oligodendrocytes: formation of
myelin in CNS.
– Microglia: phagocytic (defence).
– Schwann cells: formation of
myelin in PNS.