Neuroglia: Introduction, Classification and Functions

  • 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:

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

  • 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.

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

  1. Nerve fibres in CNS gets myelination where Schwann cells are absent.
  2. 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