Neuroglia or glia (glia = glue) is the supporting cell of the nervous system. Neuroglial cells are non-excitable and do not transmit nerve impulse (action potential). So, these cells are also called non-neural cells or glial cells. When compared to the number of neurons, the number of glial cells is 10 to 15 times greater. Neuroglial cells play an important role in the reaction of nerve duringinfection. Most commonly, neuroglial cells constitute the site of tumors in nervous system.
CLASSIFICATION O NEUROGLIAL CELLS
Neuroglial cells are
distributed in central nervous system (CNS) as well as peripheral nervous
system
(PNS).
Accordingly the neuroglial cells are classified two types:
A. Central neuroglial
cells
B. Peripheral neuroglial
cells.
CENTRAL NEUROGLIAL CELLS
Neuroglial cells in CNS
are of three types:
1. Astrocytes 2. Microglia
3. Oligodendrocytes.
ASTROCYTES
Astrocytes are star-shaped
neuroglial cells present in all the parts of the brain. Two types of
astrocytes are found in
human brain:
i. Fibrous astrocytes
ii. Protoplasmic
astrocytes.
Fibrous Astrocytes
Fibrous astrocytes occupy
mainly the white matter. Few fibrous astrocytes are seen in
gray matter also.
The processes of these cells
cover the nerve cells and synapses. This type of astrocytes play an important role
in the formation of blood-brain barrier by sending processes to the blood
vessels of brain, particularly the capillaries, forming tight junction with
capillary membrane. Tight junction in turn forms the blood-brain barrier.
Protoplasmic Astrocytes
Protoplasmic astrocytes
are present mainly in gray matter. The processes of neuroglia run between nerve
cell bodies.
Functions of
Astrocytes
Astrocytes:
i. Twist around the nerve
cells and form the supporting network in brain and spinal cord
ii. Form the blood-brain
barrier and thereby regulate the entry of substances from blood into
brain tissues
iii. Maintain the chemical
environment of ECF around CNS neurons
iv. Provide calcium and
potassium and regulate neurotransmitter level in synapses
v. Regulate recycling
of neurotransmitter during synaptic transmission.
MICROGLIA
Microglia are the smallest
neuroglial cells. These cells are derived from monocytes and enter the tissues
of nervous system from blood. These phagocytic cells migrate
to the site of infection or injury and are often called the macrophages
of CNS.
Functions of
Microglia
Microglia:
i. Engulf and destroy the
microorganisms and
cellular debris by means of phagocytosis
ii. Migrate to the injured
or infected area of CNSand act as miniature macrophages.
OLIGODENDROCYTES
Oligodendrocytes are the
neuroglial cells, which produce myelin sheath around the
nerve fibers in CNS.
Oligodentrocytes are also
called oligodendroglia. Oligodendrocytes have only few
processes, which are short.
Functions of
Oligodendrocytes
Oligodendrocytes:
i. Provide
myelination around the nerve fibers in
CNS where Schwann cells
are absent
ii. Provide
support to the CNS neurons by forming a semi-stiff connective tissue
between the
neurons.
PERIPHERAL NEUROGLIAL CELLS
Neuroglial cells in PNS
are of two types:
1. Schwann cells
2. Satellite cells.
SCHWANN CELLS
Schwann cells are the major
glial cells in PNS.
Functions of Schwann
Cells
Schwann
cells:
i. Provide
myelination (insulation) around the nerve fibers in
PNS
ii. Play important role in
nerve regeneration
iii. Remove cellular
debris during regeneration by their phagocytic activity.
SATELLITE CELLS
Satellite cells are the
glial cells present on the exterior surface of PNS neurons.
Functions of
Satellite Cells
Satellite
cells:
i. Provide physical
support to the PNS neurons
ii. Help in regulation of
chemical environment of ECF around the PNS neurons.
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