Lecture Notes: Anatomy of the Spinal Cord

Protective Structures of the Spinal Cord

• Spinal Cord Overview:

  • Bundle of nerves suspended in cerebrospinal fluid for protection and nourishment.
  • Protected by meninges and vertebral bodies.

• Vertebral Canal:

  • Created by stacking vertebrae; forms a tunnel for the spinal cord.
  • Intervertebral foramina allow spinal nerves to enter and exit.

• Meninges:

  • Continuous with cranial meninges.
  • Consist of dura mater, arachnoid mater, and pia mater.
  • Cerebrospinal fluid circulates between pia mater and arachnoid mater.
  • Epidural space: Cushion of fat and connective tissue.

External Anatomy of the Spinal Cord

• Extension:

  • Extends from the medulla oblongata to the inferior border of the second lumbar vertebra.
  • In adults, does not extend the full length of the vertebral column.

• Shape and Size:

  • Oval shape, maximum diameter about 1.5 cm.
  • Thinner in thoracic region.

• Enlargements:

  • Cervical Enlargement:
    • In the lower neck region.
    • Nerves to/from upper limbs arise here.
  • Lumbar Enlargement:
    • Located around the lower three ribs.
    • Nerves to/from lower limbs arise here.

Internal Anatomy of the Spinal Cord

• Transverse Section:
  • White matter surrounds a butterfly-shaped gray matter core.
  • Gray Matter:
    • Contains neuron cell bodies, dendrites, axon terminals, and neuroglia.
    • Divided into horns:
      • Posterior (Dorsal) Horn: Interneurons and sensory neurons.
      • Anterior (Ventral) Gray Horn: Somatic motor neurons.
      • Lateral Gray Horn: Autonomic motor neurons (thoracic and upper lumbar regions).
  • White Matter:
    • Divided into columns:
      • Anterior (Ventral) Column
      • Posterior (Dorsal) Column
      • Lateral Columns
    • Contains tracts for ascending sensory and descending motor signals.

Spinal Nerves

• Spinal Nerves Overview:

  • 31 pairs emerge from the spinal cord through intervertebral foramina.
  • Connect spinal cord to the body via roots and rootlets:
    • Posterior (Dorsal) Root and Rootlets:
      • Contain sensory axons.
      • Swelling at posterior root houses sensory neuron cell bodies (posterior root ganglion).
    • Anterior (Ventral) Root and Rootlets:
      • Contain motor axons.
      • Conduct signals from CNS to muscles and glands.

• Identification Tip:

  • Posterior root ganglion helps identify dorsal side of the spinal cord.

Key Terms

• Vertebral Foramen: Hole in vertebra for spinal cord.
• Intervertebral Foramina: Holes for spinal nerve exit.
• Cervical/Lumbar Enlargement: Thickenings in spinal cord for limb nerves.
• Gray Horns: Regions in gray matter for specific neuron types.
• White Columns: Regions in white matter for axon tracts.
• Spinal Nerve: Mixed nerve for communication between spinal cord and body.
• Roots and Rootlets: Connection points for spinal nerves, separating sensory and motor functions.