Nerve Degeneration and Regeneration

Nerve Degeneration and Regeneration

• Retrograde degeneration occurs in the nerve cell and proximal part of the nerve fiber.
  • Chromatolysis: Disappearance of Nissl bodies, decrease in basophilia, increase in perikaryon volume, loss of dendrites, migration of nucleus to periphery, Golgi body and mitochondria disappearance, neurofibril fragmentation, and lysosome increase.
• Wallerian degeneration occurs in the distal part of the nerve fiber.
  • Axon: Neurofibrils become beaded, segmented, granular, and finally disappear.
  • Myelin sheath: Widening of nodes of Ranvier, internodal segments become "fermentation chambers."
  • Schwann cells: Proliferate, forming cellular columns that guide growing axons during regeneration.
• Stains used for degeneration:
  • Silver: Demonstrates changes in Golgi body and neurofibrils.
  • Osmic acid: Demonstrates changes in the myelin sheath.
  • Basic stains: Demonstrates changes in Nissl bodies.
• Regeneration of nerve fibers:
  • Macrophages: Remove debris and secrete interleukin-1, stimulating Schwann cells to secrete nerve growth-promoting substances.
  • Growth of axons: Occurs in the proximal part in the direction of Schwann cell columns.
  • Efficient regeneration requires proper alignment of fibers and Schwann cell columns.

Central Neuroglia

• Astrocytes:
  • Cytoplasmic astrocytes: Found in gray matter, granular cytoplasm, many short processes.
  • Fibrous astrocytes: Found in white matter, fibrous cytoplasm, many long processes.
• Satellite cells:
  • Found in gray matter, closely associated with neuron cell bodies.
• Interfascicular:
  • Found in white matter, between bundles of axons.
• Functions of astrocytes:
  • Metabolic exchange control: Processes with expanded end feet linked to blood capillary endothelium regulate exchange.
  • Blood brain barrier:
  • Structural support:
  • Repair process: Formation of scar tissue.

Peripheral Neuroglia

• Schwann cells:
  • Found in the peripheral nervous system, responsible for myelin production, electrical insulation, and regeneration.
  • Origin: Ectodermal.
• Satellite cells:
  • Low cuboidal cells found in the peripheral nervous system.
  • Location: Surround nerve cells in ganglia.

Ependymal Cells

• Location: Line the central canal of the spinal cord and ventricles of the brain.
• Structure: Form a simple cuboidal or columnar epithelium, may be ciliated.
• Function: Cilia may be involved in cerebrospinal fluid (CSF) propulsion.
• Origin: Ectodermal.