Download Nerve Fibers

NERVOUS SYSTEM-2
Sixth lecture
By
Dr. Wahda A. M. Kharofa
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Objectives:
To give information about:
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Peripheral nervous system (PNS).
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Peripheral nerve.
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Neuroglia.
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Types of neuroglia.
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Spinal ganglia.
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Autonomic ganglia.
The Peripheral Nervous System (PNS)
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The main components of peripheral nervous
system are the nerves, ganglia, and nerve
ending
Nerves: are bundles of nerve fiber surrounded by
a series of connective tissue sheaths
Nerve Fibers: consist of axons enveloped by a
special sheath derived from cells of ectodermal..In
peripheral nerve fibers the sheath cell is the
schwann cell, and in central nerve fibers it’s the
oligodendrocyte.
Myelinated nerve fibers:
myelin sheath which surrounds the
axon and shows gaps along the
length of the axon, they are called
"Nodes of Raniver", represent the
spaces between schwann cells. The
distance between two nodes is
called an "Internode" and consists of
one schwann cell.
Unmyelinated nerve fibers:
absence of myelinated sheath
and the axon is covered with
schwans sheath, and they do
not have nodes of ranvier
because are united to form a
continuous sheath.
Peripheral Nerve :
It is a cord like structure firmer than the other parts of
the nervous tissue due to presence of large amount of
collagen fibers . the peripheral nerve is formed either of
one bundle or more than one bundle depending upon
the size of the nerve . Each peripheral nerve is
surrounded by a c.t. called epineurium from which a
septa arise to surround each bundle of nerve fibers this
c.t. called perineurium . each bundle consist of a number
of nerve fibers ( axon with surrounding sheath ) which
are either myelinated or non- myelinated . the nerve fiber
is surrounded by a c.t. called endoneurium.
Neuroglia :
Cells whose function is the metabolic and mechanical support and
protection of neurons form the nuuroglia .
There are many types of neuroglial cells as shown:
2- Oligodendrocytes:
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These cells are small and contain fewer processes,
with sparse branching, and they are located in both gray
and white matter of CNS. The cytoplasm contains small
nucleus. These cells producing a myelin sheath.
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4- Microglia: 
These cells are small elongated, with short irregular
processes. These cells function as phagocytes in
clearing debris and damaged structures in the CNS.
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Ganglia :
The ganglia are nodules that contain an aggregation of the cell
bodies of neurons.
There are two kinds of ganglia:
1- Spinal ganglia:
They are present in the dorsal root of the spinal nerves & it
also present in cranial sensory nerves, it is rounded or oval in shape
surrounded from outside by a c.t. capsule which is the continuous of
epineurium of the nerve which connected to it , this c.t. extends inside
the ganglion & divided it into groups of cells .Each cell is enveloped by
a double layers, the outer one is a c.t. ( fibers with fibroblast ) which is
a continuous of the endoneurium. The inner layer is called satellite
cells applied closely to the ganglion cells.
The cells are of pseudounipolar, most of them are large
spherical in shape . the fibers which are present inside the ganglion
are of myelinated type. Each cell contains a centrally located nucleus.
Nissle granules are scattered in the cytoplasm.
2- Autonomic ganglia: it's structure similar to
spinal ganglia but there are some differences
between them which are:
a- the nerve cell is of multipolar type & smaller
than that of spinal ganglia .
b- the nucleus of the nerve cell is eccentric in
position which is oval or rounded with one or two
nucleolus .
c- the nerve fibers are of non – myelinated type .
d- the ganglion cells surrounded by less satellite
cells .
e- the cells are not arranged in groups but they
scattered irregularly .