Lecture on Spinal Cord and Nerves

Structure of the Spinal Cord

• Begins at the superior end through the largest opening in the skull, the foramen magnum.
• Ends at L1 or L2 vertebrae in adults.
• Below L1 or L2, the space is occupied by nerves extending off the spinal cord.
• Growth in humans: Spinal cord does not grow as much as nerves that extend from it.

Protection of the Spinal Cord

• Similar to brain protection:
  • Bone: Vertebrae (instead of cranial bones).
  • Meninges: Three layers surrounding both brain and spinal cord:
    • Dura mater: Thick and inelastic.
    • Arachnoid mater: Spider-web-like structure.
    • Pia mater: Delicate layer directly on the spinal cord.
  • Cerebrospinal Fluid (CSF): Same fluid as around the brain.

Functions of the Spinal Cord

• Two-way communication between the brain and body.
• Important reflex center; many reflexes completed at spinal cord level.

Spaces Associated with Spinal Cord

• Epidural Space: Between bone and dura mater; used for anesthetics (e.g., epidurals).
• Subdural Space: Below dura mater, between dura and arachnoid mater.
• Subarachnoid Space: Below arachnoid mater; CSF flows here.

Spinal Nerves

• Part of the peripheral nervous system.
• 31 paired roots; named for their exit location in the spinal column.
• Form nerve plexuses by interweaving with other nerves.
• Mixed nerves: Sensory and motor.

Enlargements and Tapering

• Cervical Enlargement: Due to upper limb nerves joining spinal cord.
• Lumbar Enlargement: Due to lower limb nerves joining spinal cord.
• Conus Medullaris: Tapering end of the spinal cord at L1 or L2.
• Cauda Equina: Nerves extending below L1/L2, resembling a horse's tail.
• Filum Terminale: Anchors spinal cord to coccyx; not a nerve.

Cross-section of the Spinal Cord

• Grey Matter: Center, appears as H or butterfly shape; contains unmeylinated neurons.
• White Matter: Periphery, myelinated axons.
• Central Canal: Contains CSF, runs entire spinal cord length.

Horns and Columns

• Grey matter divided into anterior, lateral, and posterior horns.
• White matter divided into anterior, lateral, and posterior columns (funiculi).

Pathway Orientation

• Anterior/Ventral Root: Motor information exits.
• Posterior/Dorsal Root: Sensory information enters; contains dorsal root ganglion.
• Sensory pathways are ascending; motor pathways are descending.

Dermatomes

• Nerves create a map on the skin indicating spinal nerve innervation.
• Used in diagnostics and treatments (e.g., referred pain from internal organs).

Clinical Views

• Shingles: Chickenpox virus reactivates in adulthood; follows dermatome path.
• Spinal Cord Injuries: Classified by affected limbs (e.g., monoplegia, paraplegia).
• Lumbar Puncture: Collects CSF for analysis; performed below L1/L2 to avoid spinal cord injury.