Cytoarchitecture of the Nervous System

Introduction

• Lecture by Dr. Catherine Moore, focusing on nervous system structures.
• Importance of definitions due to different terminologies in CNS and PNS.

Key Definitions

• CNS (Central Nervous System): Collections of neurons called nuclei.
• PNS (Peripheral Nervous System): Collections referred to as ganglia.
• Enteric Nervous System: Groups of neurons called plexi.
• Tracts: Bundles of axons in CNS.
• Nerves: Bundles of axons in PNS.
• Basal Ganglia: Notable exception in CNS terminology.
• Cortex & Retina: Regions with specific layers of neurons.

Peripheral Nervous System (PNS) Structures

• Peripheral Ganglia: Collections of neuronal cell bodies.
  • Sympathetic Ganglion: Located ventral and lateral to the spinal cord; involved in stress responses.
  • Dorsal Root Ganglia: Sensory ganglion; transmits afferent signals to CNS; contains pseudo unipolar neurons.
  • Satellite Cells: Schwann cells around neurons, not to be confused with skeletal muscle satellite cells.
  • Enteric Ganglia/Plexi: Found in the digestive tract, involved in gut motility; can function independently.

Disorders Related to Enteric Nervous System

• Akalasia: Difficulty swallowing.
• Hirschsprung Disease: Can lead to megacolon.

Structure of Peripheral Nerves

• Composed of axons from sensory and motor neurons, associated with Schwann cells.
• Connective Tissue Layers:
  • Endoneurium: Surrounds individual axons.
  • Perineurium: Surrounds fascicles of axons, thicker with blood vessels and immune cells.
  • Epineurium: Outer covering of large nerves, dense irregular connective tissue.

Central Nervous System (CNS) Structures

• Components: Gray matter (cell bodies, dendrites, synapses) and white matter (myelinated/unmyelinated axons).
• Staining: Nissl stain used to visualize gray matter, which marks rough endoplasmic reticulum.
• Cells Present: Astrocytes, oligodendrocytes, microglia in both gray and white matter.

CNS Organization

• Brain organized similarly to spinal cord.
• Gray matter in cortex and cerebellum organized into layers; standard stains may not reveal layers well.

Support Tissues in CNS

• Meninges: Protective connective tissue layers around the brain.

  • Dura Mater: Outermost layer, attached to the skull, has blood vessels and nerve fibers.
  • Arachnoid Mater: Middle layer; contains trabeculae and subarachnoid space filled with CSF.
  • Pia Mater: Innermost layer, covers CNS surface, contains blood vessels and nerves.

• Cerebral Spinal Fluid (CSF): Produced in ventricles, bathes CNS cells, removed via arachnoid villi.

• Ependymal Cells: Line central canal, assist in CSF production and waste removal.

Choroid Plexus

• Responsibility for CSF production and regulation.
• Formed by pia mater extensions covered in ependymal cells.

Blood-Brain Barrier (BBB)

• Specialized capillaries limit access to the CNS, protects against toxins.
• Tight Junctions: Between endothelial cells restrict substance movement.
• Astrocyte End Feet: Help maintain the BBB structure.

Conclusion

• Overview of cytoarchitecture in the nervous system.
• Encouragement to engage with other educational resources.