Classification Of Neuroglial Cells Notes

Neuroglia Definition

• Neuroglia or the glia (glia = glue) is the support of the nervous system. The neuroglial cells are nonexcitable and do not transmit nerve impulses (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 10-15 times greater. The neuroglia plays an important role in the reaction of nerve during infection. Most commonly, the neuroglial cells constitute the site of tumors in the nervous system.

Classification Of Neuroglial Cells

The neuroglial cells are distributed in the central nervous system (CNS) as well as the peripheral nervous system (PNS). Accordingly, the neuroglial cells are classified into two types:

1. Central neuroglial cells
2. Peripheral neuroglial cells.

Read And Learn More: Medical Physiology Notes

Central Neuroglial Cells: The neuroglial cells in CNS are of three types

1. Astrocytes
2. Microglia
3. Oligodendrocytes.

1. Astrocytes: Astrocytes are star shaped neuroglial cells present in all the parts of the brain. Two types of are found in human brain:

1. Fibrous astrocytes
2. Protoplasmic astrocytes.
   1. Fibrous Astrocytes
      • The fibrous astrocytes occupy mainly the white matter. Few fibrous astrocytes are seen in the gray matter also. The processes of these cells cover the nerve cells and synapses.
      • This type of astrocyte play an important role in the formation of the blood-brain barrier by sending processes to the blood vessels of brain, particularly the capillaries, forming tight junction with the capillary membrane. The tight junction in turn forms the blood-brain barrier.
   2. Protoplasmic Astrocytes: Protoplasmic astrocytes are present mainly in gray matter. The processes of the neuroglia run between the nerve cell bodies.
      • Functions of Astrocytes
        1. Twist around the nerve cells and form the supporting network in brain and spinal cord
        2. Form the blood-brain barrier and thereby regulate the entry of substances from blood into brain tissues
        3. Maintain the chemical environment of ECF around CNS neurons
        4. Provide calcium and potassium and regulate neurotransmitter level in synapses
        5. Regulate recycling of neurotransmitters during synaptic transmission.

2. Microglia: Microglia are the smallest neuroglial cells. These cells are derived from monocytes and enter the tissues of the 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
  1. Engulf and destroy the microorganisms and cellular debris by means of phagocytosis
  2. Migrate to the injured or infected area of CNS and act as miniature macrophages.

3. Oligodendrocytes: Oligodendrocytes are the neuroglial cells that produce myelin sheath around the nerve fibers in CNS. Oligodendrocytes are also called oligodendroglia. The oligodendrocytes have only a few processes, which are short.

• Function of Oligodendrocytes
  1. Provide myelination around the nerve fibers in CNS where Schwann cells are absent
  2. Provide support to the CNS neurons by forming a semi-stiff connective tissue between the neurons.

Peripheral Neuroglial Cells

The neuroglial cells in PNS are of two types:

1. Schwann cells
2. Satellite cells

 

1. Schwann Cells: Schwann cells are the major glial cells in PNS.
   • Functions of Schwann Cells
     1. Provide myelination (insulation) around the nerve fibers in PNS
     2. Play an important role in nerve regeneration
     3. Remove cellular debris during regeneration by their phagocytic activity.
2. Satellite Cells: Satellite cells are the glial cells present on the exterior surface of PNS neurons.
   • Functions of Satellite Cells
     1. Provide physical support to the PNS neurons
     2. Help in regulation of the chemical environment of ECF around the PNS neurons.