Neuroglia: Introduction, Classification and Functions

September 25, 2021

The supporting cells of the nervous system that are non-excitable are called neuroglia or simply glia (glia=glue).
They do not transmit nerve impulse (action potential) for which they are called non-neural cells or glial cells.
They are about 10-15 times greater than the number of neurons.
During infection, mostly they show or play an important role in the reaction of the nerve.
They mostly constitute the site of tumors in nervous system.

Image source: Science news Image source: Anatomy corner

Classification

These cells are distributed both in central nervous system (CNS) and peripheral nervous system (PNS).
According to their distribution in both CNS and PNS, they are classified into two types. They are:

A) Central Neuroglial Cells

i) Astrocytes

These are star shaped neuroglial cells and are present in all the parts of brain.
These cells are also of two types .They are

a) Fibrous astrocytes

These cells mostly occupy the white matter of brain and few are also noticed in gray matter.
The processes that are present in these cells cover the nerve cells and synapses.
They show a great role in formation of blood-brain barrier by sending processes to the blood vessels of the brain.
The blood vessels involved are mostly capillaries and the formation of tight junction with the capillary membrane occurs which in turn forms the blood-brain barrier.

b) Protoplasmic astrocytes

Functions of Astrocytes

Help in forming supporting network in brain and spinal cord by twisting around the nerve cells.
Help in regulating the exchange of substances from blood into brain tissues by forming the blood-brain barrier.
Help in balancing the chemical environment of ECF around the CNS neurons.
Help in regulating neurotransmitter level in synapses is regulated by providing calcium and potassium.
Also help to regulate the recycling of neurotransmitter during synaptic transmission.

ii) Microglia

These are the neuroglial cells derived from monocytes and are the smallest of all that enter the tissues of nervous system from the blood.
They migrate to the site of infection or injury as they are phagocytic in nature.
For that, they are considered macrophage of CNS.
These neuroglial cells are mesodermal in origin as compared to other neuroglial elements.

Functions of Microglia

Through phagocytosis, engulfing and destroying of microorganisms and cellular debris occurs.
Act as miniature macrophages by migrating to the injured or infected area of CNS.

iii) Oligodendrocytes

These are the myelin sheath producing neuroglial cells around the nerve fibres in CNS.
They are also called oligodendroglia which has short and only few processes.

Functions of Oligodendrocytes

Nerve fibres in CNS gets myelination where Schwann cells are absent.
Forms a semi-stiff connective tissue between the neurons thus providing support to the CNS neurons.

B) Peripheral Neuroglial Cells

a) Schwann cells

These are the major glial cells in PNS having flattened and elongated nuclei.
They form sheaths for axons of peripheral nerves and are also called lemnocytes or peripheral glia.

Functions of Schwann cells

Nerve fibres in PNS get myelination mostly for insulation.
Shows a great role in nerve regeneration.
By their phagocytic activity, removal of cellular debris during regeneration occurs.

b) Satellite cells

The exterior surface of the PNS neurons contains the glial cells called satellite cells.
They are also called capsular gliocytes or capsular cells.

Functions of Satellite Cells

References

I am Shailesh Koirala