Neuroglia (Glial Cells) in the Nervous System

Overview

• Neuroglia (or glia) make up about half the volume of the central nervous system (CNS).
• Term "glia" derived from the idea of being the "glue" that holds the nervous system together.
• Neuroglia are smaller than neurons but 5 to 25 times more numerous.
• They do not generate or propagate action potentials.
• Six types of neuroglia: four in the CNS, two in the peripheral nervous system (PNS).

Neuroglia in the Central Nervous System

1. Astrocytes

• Characteristics: Largest and most numerous neuroglia; star-shaped with many processes.
• Functions:
  • Provide structural support for neurons.
  • Form part of the blood-brain barrier to protect brain tissue.
  • In embryos, regulate the growth, migration, and interconnection of neurons.
  • Maintain chemical environment for action potential generation.
  • Serve as a passageway for nutrients between capillaries and neurons.
  • Store glycogen and potentially influence learning and memory.

2. Oligodendrocytes

• Characteristics: Cells with processes that wrap around the axons of neurons.
• Functions:
  • Form and maintain the myelin sheath.
  • Protect axons and assist in action potential propagation.
  • A single oligodendrocyte can myelinate multiple neurons.

3. Microglia

• Characteristics: Small cells with thin processes having spines.
• Functions:
  • Act as phagocytes, removing cellular debris and damaged tissue.
  • Clean up microbes in the CNS.

4. Ependymal Cells

• Characteristics: Cuboidal to columnar cells with microvilli or cilia lining brain ventricles and the spinal cord’s central canal.
• Functions:
  • Produce and circulate cerebrospinal fluid (CSF).
  • Form the blood-cerebrospinal fluid barrier.

Neuroglia in the Peripheral Nervous System

1. Schwann Cells

• Characteristics: Cells that wrap around neuron axons in the PNS.
• Functions:
  • Form and maintain the myelin sheath.
  • Each Schwann cell myelinates a single axon.
  • Involved in axon regeneration, more common in PNS than CNS.

2. Satellite Cells

• Characteristics: Flat cells surrounding neuron cell bodies in the PNS.
• Functions:
  • Provide structural support.
  • Facilitate exchange of nutrients and waste between neurons and interstitial fluid.

Key Differences between CNS and PNS Neuroglia

• Astrocytes and Oligodendrocytes: Present only in the CNS.
• Schwann and Satellite Cells: Present only in the PNS.
• Schwann cells are similar to oligodendrocytes but each Schwann cell myelinates only one axon, while oligodendrocytes can myelinate multiple.
• Axon regeneration is more feasible in PNS due to Schwann cells.

These notes provide a comprehensive overview of the role and types of neuroglia in both the central and peripheral nervous systems, highlighting their functions and differences.