Lecture Notes on the Spinal Cord

Overview

• Part of the central nervous system.
• Composed of white matter and gray matter:
  • Gray Matter: Composed of unmyelinated axons, interneurons, somas, and dendrites. Shaped like an "H" or butterfly.
  • White Matter: Composed of myelinated axons, surrounds the gray matter.

Meninges

• Spinal cord is surrounded by protective layers called meninges:
  1. Dura Mater: Outermost, thick and tough layer.
     • Subdural space (in 50% of people) may contain cerebrospinal fluid (CSF).
  2. Arachnoid Mater: Middle layer, web-like appearance.
     • Subarachnoid space contains CSF; site for spinal taps.
  3. Pia Mater: Innermost, thin layer that adheres to the spinal cord.

Nerves and Enlargements

• Cervical Nerves: 8 pairs, despite only 7 cervical vertebrae.
• Thoracic Nerves: 12 pairs.
• Lumbar Nerves: 5 pairs.
• Sacral Nerves: 5 pairs.

Enlargements

• Cervical Enlargement: Bulge for brachial and cervical plexus.
  • Important nerves: median, radial, ulnar.
• Lumbar Enlargement: Where nerves for lower limbs exit, forms lumbar plexus.
• Conus Medullaris: End of the spinal cord.
  • Cauda Equina: Collection of nerve roots like a "horse's tail".
  • Filum Terminale: Extension made of pia mater, attaching to the coccyx.

Plexuses

• Cervical Plexus: Upper braided network of nerves.
• Sacral Plexus: Includes the sciatic nerve, the largest in the body.

Anatomy of the Spinal Cord

• Posterior Median Sulcus: Indentation on the back of the spinal cord.
• Anterior Median Fissure: Front indentation, deep into gray matter.

White and Gray Matter

• White Matter Columns:
  • Posterior columns (back)
  • Lateral columns (sides)
  • Anterior columns (front)
• Gray Matter Horns:
  • Posterior gray horn: Receives axons from incoming neurons.
  • Anterior gray horn: Contains cell bodies of neurons exiting the spinal cord.
  • Lateral gray horn: Only in thoracic and lumbar regions.

Central Canal and Commissures

• Central Canal: Circulates CSF.
• Gray Commissure: Connects sides of gray matter.
• White Commissure: Connects sides of white matter.

Nerve Pathways

• Sensory Information: Enters through the back (dorsal roots).
  • Sensory neurons are typically unipolar.
• Motor Information: Exits through the front (motor roots).
  • Motor neurons can be somatic (voluntary) or autonomic.

Spinal Nerves

• Merge of sensory and motor roots.
• Mixed Nerves: All spinal nerves contain both sensory and motor fibers.

Integration and Interneurons

• Interneurons: Facilitate integration in gray matter.
  • Integration can be monosynaptic or polysynaptic.
• Thoracic Cross-section: Shows presence of lateral gray horns with autonomic motor neuron cell bodies.

This concludes the overview of spinal cord structure, nerve pathways, and related anatomical features.