Nervous System Histology Lecture Notes

Introduction

• Cells named after stars and neurons branching like bare trees.
• Nervous system beautiful yet cluttered under a microscope.
• Focus: Understanding the histology of nervous system cells.

Overview of the Nervous System

• Central Nervous System (CNS): Brain and spinal cord.
• Peripheral Nervous System (PNS): Nerves branching out from CNS.
• Purpose: Send and receive electrical signals.

Neurons and Nerve Structure

• Nerves are clusters of neurons, like power lines in a city.
• Transverse Cross-Section of Nerve: Shows neuron clusters.
• Longitudinal View: Reveals long axons.
• Connective tissue around nerves follows muscle naming conventions:
  • Epineurium: Dense outer connective tissue.
  • Perineurium: Wraps each bundle (fascicle) of neurons.
  • Endoneurium: Wraps each neuron and its accessories.

Neuron Anatomy

• Neurons are cells with DNA and organelles.
• Soma (Cell Body): Contains nucleus.
• Dendrites: Branches collecting electrical impulses.
• Axon Hillock: Summation of impulses.
• Axons: Long parts, can be over 95% of neuron cell volume and over a meter long.
• Axon Terminals: End of neuron, send neurotransmitters to other cells.

Neuron Diversity and Types

• Myelinated vs. Unmyelinated Neurons:
  • Myelin Sheath: Speeds up signal transmission.
  • Type Ia Fibers: 4-20 micrometers wide, fast conduction.
  • Type B Fibers: 1-4 micrometers wide.
  • Type C Fibers: 0.2-1.5 micrometers wide, slower conduction.
• Branching Patterns:
  • Multipolar Neurons: Common in brain and spinal cord.
  • Bipolar Neurons: Found in sensory systems like nose and retina.
  • Unipolar Neurons: Single axon, no dendrites.

Glial Cells

• Astrocytes: Star-shaped, support/protect neurons.
• Oligodendrocytes: Form myelin in CNS.
• Schwann Cells: Form myelin in PNS.

Central Nervous System (CNS) Tissue

• White Matter: Myelinated fibers, looks like marshmallows.
• Gray Matter: Unmyelinated fibers, slow conduction.
• Spinal Cord Cross-Sections:
  • "Butterfly pancake" view: Anterior, lateral, and dorsal horns.

Brain Overview

• Meninges: Layers surrounding the brain.
  • Dura Matter: Dense outer layer.
  • Arachnoid Layer: Thin layer, spider web-like.
  • Pia Matter: Delicate inner layer.
• Brain Tissue:
  • Cerebral Cortex: Outer layer, has 6 layers.
  • Subcortical White Matter: Deeper layer.
  • Pyramidal Neurons: Dark blue, large nuclei.

Conclusion

• Importance of understanding neuroanatomy.
• Further resources available in accompanying videos and notes.