2. Nervous Tissue
• Nervous tissues are of two types:
• Neurons
• Neuroglial Cells (Supporting cells)
3.
4. Difference Between Neuron and Neuroglial Cells:
1. Neuron :
• Excitable cells
• Generate action potential
• is the basic structural and functional unit of nervous system
• Present in CNS,PNS and ANS
5. Difference Between Neuron and Neuroglial Cells:
2. Neuroglial cells (Glia literally means “GLUE”)
• Non-excitable cells .
• Do not generate action potential
• is the supporting tissue
• 10-times more abundant in mammalian brain than neurons
• Present in CNS
6. Neuroglial Cells (Supporting Cells):
Six types of supporting cells are present in CNS
• Four in the CNS
• Two in the PNS
7. Characteristics of neuroglial cells:
• Much smaller than neurons and more numerous (10 : 1)
• Make up half the mass of the brain
• Do not generate and propagate action potentials
• They can replace themselves
• They have branching processes
• They can divide throughout life
8. Four types of neuroglia in CNS:
• Oligodendrocytes-
• ( Myelinating cells )
• Astrocytes –
• (Blood-brain barrier (BBB)
• Microglia –
• ( Phagocytes (from bone marrow)
• Ependymal cells -
• (Line ventricles of brain; produce cerebrospinal fluid (CSF)
Two Types Of Neuroglia Of The PNS:
• Schwann cells –
• Myelinating cells,
• Helps in axon regeneration
• Satellite cells
• Support, protection, regulation of molecular exchange
10. Neuroglia in the CNS:
1.Astrocytes : are the largest and most abundant glial cell of
CNS.
Star shaped (derived their name from the Greek astron,
“star”)
11. Functions of 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.
12. 2. Microglia – smallest and least abundant glial cell
• 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
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.
13. 3. Ependymal cells
• These cells Line the central cavity of the spinal cord and
brain cilia
• help circulate the cerebrospinal fluid
14. 4. Oligodendrocytes
• Smaller than astrocytes and have fewer processes
• Literally means “cell with few branches” (oligo few; dendro branch; cyte cell)
• Some lie clustered around nerve cell bodies
• Some are arranged in rows between nerve fibers in the brain and spinal cord
• Function is to help
• Provide support &hold nerve fibers together by forming
a semi-stiff connective tissue between the neurons.
• Provide myelination around the nerve fibers in CNS where Schwann cells are
absent
15. 5. Schwann Cells
• Only found in the PNS
1. Provide myelination (insulation) around the
nerve fibers in PNS
2. Play important role in nerve regeneration
3. Remove cellular debris during regeneration
by their phagocytic activity.
16.
17. 6. Satellite cell
Satellite cells are the glial cells present on the exterior
surface of PNS neurons.
• They surround the cell body of a neuron
1. They support neuronal cell bodies
in regions called GANGLIA in the PNS
2. Help in regulation of chemical environment of ECF
around the PNS neurons.
