Neuroglia function and classification

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.

Neuroglia function and classification


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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