Lecture on Neuroglia (Glial Cells)

Overview of Nervous Tissue

• Nervous tissue consists of two major cell types:
  • Neurons: Excitable cells that transmit electrical signals for high-speed communication.
  • Neuroglia (Glial Cells): Cells that outnumber neurons about 10:1, support and protect neurons.

Types of Neuroglia in the Central Nervous System (CNS)

1. Astrocytes

   • Most abundant glial cell.
   • Star-shaped, highly branched (Astro = star, Cyte = cell).
   • Functions:
     • Support and brace neurons.
     • Facilitate exchange between capillaries and neurons (part of blood-brain barrier).
     • Guide neuronal development by scaffolding.
     • Regulate chemical environment around neurons.
     • Involved in information processing and communication.
   • Visual: Star-shaped with extensions wrapping around blood vessels.

2. Microglial Cells

   • Small, ovoid with thorny processes.
   • Immune defense cells in the CNS.
   • Functions:
     • Migrate to injured neurons and transform to phagocytize microorganisms and debris.
     • Involved in immune response and inflammation.
   • Visual: Thorny cells, activated by chemicals and microorganisms.

3. Ependymal Cells

   • Shape: Squamous to columnar; may be ciliated.
   • Functions:
     • Line brain cavities and spinal cord.
     • Circulate cerebrospinal fluid (CSF) which nourishes and protects the brain.
   • Visual: Line up like an epithelium, form a barrier between CSF and ventricles.

4. Oligodendrocytes

   • Large cells that form myelin sheaths around CNS nerve fibers.
   • Functions:
     • Insulate nerve fibers to speed up electrical impulses.
   • Visual: Look like insulation around electrical wires.

Types of Neuroglia in the Peripheral Nervous System (PNS)

1. Satellite Cells

   • Surround neuron cell bodies in the PNS.
   • Function similar to CNS astrocytes (protect and monitor environment).

2. Schwann Cells (Neurolemmocytes)

   • Surround PNS nerve fibers.
   • Functions:
     • Form myelin sheath like oligodendrocytes.
     • Assist in regeneration of damaged peripheral nerves by guiding axon reconnection.
   • Essential for peripheral nerve repair.

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Additional Notes

• CNS and PNS have different types of glial cells due to different developmental pathways.
• Astrocytes play a crucial role in maintaining the brain's extracellular environment and monitoring synapses for communication.
• Microglial cells act as the brain's immune system, clearing out dead tissue post-injury (e.g., stroke).