- 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.
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- 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
- In CNS, these cells are of three different types. They are:
- 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
- Their presence is mostly noticed in gray matter.
- The processes present in the neuroglia run between nerve cell bodies.
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.
- 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.
- 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.
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B) Peripheral Neuroglial Cells
- These cells are also of two types. They are:
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
- Help by providing physical support to the PNS neurons.
- Helps in regulation of chemical environment of ECF around the PNS neurons.
Neuroglia: Introduction, Classification and Functions