Notes on the Structure and Function of the Spinal Cord

Spinal Cord Structure and Function

Overall Functionality

  • Connection to the Brain: The spinal cord is directly connected to the brain yet maintains functional independence.
  • Information Processing: It integrates and processes sensory and motor information.
  • Anatomical Extent: It begins at the medulla oblongata, extends through the foramen magnum, and ends at the inferior border of the first lumbar vertebra (L1).

Gross Anatomy

  • Regions of the Spinal Cord:
    • Cervical Enlargement: Due to the concentration of nerves serving the upper limbs.
    • Lumbar or Lumbosacral Enlargement: Houses nerves supplying the lower extremity.
    • Conus Medullaris: Terminates at L1/L2, marking the end of the spinal cord.
    • Filum Terminale: A slender extension from the conus medullaris to the coccyx, primarily made up of pia mater.
    • Cauda Equina: Bundle of spinal nerves beyond the conus medullaris that resembles a horse's tail, often accessed during spinal taps.

Anatomical Areas

  • Divisions of the Spinal Cord:
    • Cervical Region
    • Thoracic Region
    • Lumbar Region
    • Sacral Region

White Matter vs. Gray Matter

  • White Matter:
    • Outer portion of the spinal cord, primarily containing myelinated axons.
  • Gray Matter:
    • Inner portion consisting of neuronal cell bodies, dendrites, and unmyelinated fibers.

Tracts and Columns

  • Functions of Tracts:
    • Ascending Tracts: Carry sensory information from the body up to the brain.
    • Descending Tracts: Transmit motor commands from the brain to the body.
  • White Columns: Collections of myelinated tracts running up and down the spinal cord.

Spinal Cord Cross Section

  • Gray Matter Arrangement:
    • Posterior Horn: Houses sensory neuron processes.
    • Anterior Horn: Contains somatic motor neuron cell bodies.
    • Lateral Horn: Contains autonomic nerve cell bodies.
    • Gray Commissure: Area for inter-communication among horns.
    • Central Canal: Continuous with the fourth ventricle of the brain.

Spinal Cord Segments

  • Distribution of Nerves:
    • 31 Segments: Each segment corresponds to a pair of spinal nerves.
    • Dorsal Nerve Roots: Contain sensory neuron processes.
    • Dorsal Root Ganglion: Contains sensory neuron cell bodies, described as pseudounipolar.
    • Ventral Nerve Roots: House motor neuron processes.
    • Convergence: Dorsal and ventral roots unite to form a spinal nerve.

Meningeal Layers

  • Dura Mater:
    • Extends from the foramen magnum to the S2 vertebral level, forming tough outermost covering.
  • Arachnoid Mater:
    • Contains the subarachnoid space, which is filled with cerebrospinal fluid (CSF).
  • Pia Mater:
    • Innermost layer closely adhered to the neural tissue.
  • Protective Function: The meninges cover spinal nerve roots up to the point of exit through the intervertebral foramen.

Summary of Meningeal Spaces

  • Subdural Space: Space between dura mater and arachnoid.
  • Epidural Space: Space outside the dura mater.