Lecture Notes on Spinal Nerves and Nervous System

Spinal Nerves and Motor Components

• Ventral Root: Originates from the anterior horn cell.
• Motor Components:
  • Alpha Efferent: Somatic motor component.
  • Gamma Efferent: Smaller fibers, associated with muscle spindles (stretch receptors).

Structure of Spinal Nerves

• Cross-section of a Spinal Nerve:
  • Connective Tissues:
    • Endoneurium: Surrounds individual nerve fibers.
    • Perineurium: Groups fibers into bundles.
    • Epineurium: Encompasses the entire nerve.

Plexus and Nerve Formation

• Plexus (Plexi): Networks of nerves formed by recombination of spinal nerves.
  • Major Plexi:
    • Brachial Plexus: C5 to T1, forms nerves like the radial nerve.
    • Lumbosacral Plexus.
• Radial Nerve: Affects extensors of the forearm; damage leads to "wrist drop".
• Median Nerve: Affects flexors in the anterior surface; damage affects fist-making ability.

Nerve Injury and Regeneration

• Injury Factors: Depends on location.
• Degeneration and Regeneration:
  • Proximal Axon: Degenerates back to the first node of Ranvier.
  • Chomatolysis: Changes in soma, including swelling, nucleus displacement, and periphery migration of Nissl substance.
  • Distal Segment: Axon breaks up, Schwann cells multiply.
  • Regeneration: Sprouts from axon find Schwann tube, traveling 3-4mm/day.
  • Collateral Axons: Branches from axons can send signals in the absence of primary axon.

White and Gray Matter in Spinal Cord

• White Matter: Composed of Funiculi and Fasciculi.
  • Posterior Funiculus: Contains Fasciculus Gracilis (lower body) and Fasciculus Cuneatus (upper body).
• Sensory Modality: Conscious proprioception (position in space).

Pain and Temperature Pathways

• Ascending Pathway: Three neurons (primary in DRG, secondary in posterior horn, tertiary in thalamus).
  • Primary Neuron: Pseudo-unipolar cell in DRG, enters spinal cord via Lissauer’s fasciculus.
  • Secondary Neuron: Synapses in substantia gelatinosa, crosses at anterior white commissure, ascends in lateral spinothalamic tract.
  • Tertiary Neuron: Synapses in thalamus, ascends to post-central gyrus.
• Pain Types: Sharp, dull, burning, referred.
• Cultural Aspects of Pain: Varies between individuals.

Visual Aids and Examples

• Peripheral Nerve Cross-section: Shows connective tissues and vascularization.
• Dermatomes: Distribution of nerves on the body surface.
• Nerve Cell Changes: Healthy vs. injured neuron morphological changes.
• Cord Cross-sections: Locations of various tracts and fasciculus.
• Sensory Cortex and Homunculus: Representation of body parts in the sensory cortex.

Conclusion

• Understanding of spinal nerve components, nerve injury and degeneration, nerve pathways, and the functional anatomy of the nervous system.