Gross Anatomy of the Spinal Cord and Spinal Nerves

Central and Peripheral Nervous System

• Central Nervous System (CNS): Composed of the brain and the spinal cord.
• Peripheral Nervous System (PNS): Composed of nerves, including spinal nerves which have sensory and motor components (somatic and visceral).
• Connection: Spinal nerves connect the CNS to the PNS.

Anatomy of the Spinal Cord

• Start and End:
  • Begins at C1 (first cervical vertebra).
  • Ends between L1 and L2 vertebrae.
• Segments of the Spinal Cord: Each corresponds to specific regions.
  • Cervical segment
  • Thoracic segment
  • Lumbar segment
  • Sacral segment
  • Coccygeal segment
• Conus Medullaris: Tapered end of the spinal cord at L1-L2.
• Cauda Equina: Bundle of spinal nerves from L2 to coccygeal region.
• Filum terminale extends to coccygeal vetebra(pia)
• Duramater,archanoid ends at s2

Spinal Nerves

• Cervical Segment: 8 pairs
• Thoracic Segment: 12 pairs
• Lumbar Segment: 5 pairs
• Sacral Segment: 5 pairs
• Coccygeal Segment: 1 pair
• Total: 31 pairs of spinal nerves

Unique Features

• Cervical Enlargement: C5-T1, associated with upper limb skeletal muscles.(it has increased grey matter in ventral horn)
• Lumbar Enlargement: L2-S3, associated with lower limb skeletal muscles.(same)
• White and Gray Matter:
  • White Matter: Decreases as you move caudally.(cervical to cocygeal)
  • Gray Matter: Increases.

Cross Section Anatomy of the Spinal Cord

• Gray Matter: Consists of cell bodies and dendrites.
  • Posterior Gray Horn: Contains interneurons from sensory neurons whose cell bodies are outside in dorsal root ganglion.,whose axons reach spinal cord via dorsal roots
  • Ventral Gray Horn: Contains cell bodies of somatic motor neurons that send their axon out of spinal cord via ventral roots to supply muscles,glands
  • Lateral Gray Horn: Found from T1 to L2, contains sympathetic motor neurons.pre cell bodies
• White Matter: Made up of myelinated axons.
  • Dorsal Funiculus: Ascending sensory tracts.
  • Lateral and Ventral Funiculus: Both ascending and descending tracts.

Spinal Nerve Structure

• Dorsal Root: Sensory input to the spinal cord.
• Ventral Root: Motor output from the spinal cord.
• These both form spinal nerve
• Spinal nerves bifercates into:
• Dorsal Ramus: Supplies the back and neck.(deep)
• Ventral Ramus: Supplies anterior/lateral trunk and limbs.(coonected to ganglia-white and grey rami communicans)
• Ganglia: Groups of cell bodies in the PNS, specifically the dorsal root ganglia for sensory neurons.

Function of Spinal Nerves

• Sensory Pathway:
  • Sensory information from skin travels through dorsal/ventral rami and spinal nerve.
  • Enters through the dorsal root,dorsal root ganglion
  • Synapses in the dorsal gray horn.with interneuron then motor (in ventra horn)
• Motor Pathway:
  • Motor response travels through the ventral root and spinal nerve.
  • Can exit via dorsal or ventral rami to respective muscle targets.
• Mixed Fibers: Spinal nerves contain both sensory and motor fibers.

• Protection of the Spinal Cord – Basic Points

  1. Spinal Cord Protection Layers:
     • Protected by:
       - Bones (vertebrae)
       - Meninges (protective layers)
       - Cerebrospinal fluid (CSF)
  2. Dura Mater (Outer Meningeal Layer):
     • In the spinal cord, it’s called the
     • spinal dural sheath.
     • Unlike in the brain, it does not attach
     • to the bone.
     • Only connects to the meningeal layer
     • of the brain’s dura.
  3. Epidural Space:
     • Located outside the spinal dura.
     • Contains:
       - Cushioning fat
       - Network of veins
     • Epidural anesthesia is given here to block pain in lower body areas.
  4. Other Meninges & Spaces:
     • Spaces and layers around the spinal cord (subdural space, arachnoid mater, subarachnoid space, pia mater) are continuous with the brain.
  5. Extension of Meninges:
     • Dura and arachnoid mater extend down to S₂ vertebra (lower end of spinal cord).
     • Pia mater goes even further—attaches to coccyx via filum terminale.
  6. Denticulate Ligaments:
     • These are lateral extensions of pia mater.
     • Function: Anchor the spinal cord sideways to the dura mater.

.Conclusion

• Understanding the anatomy and function of the spinal cord and nerves is crucial for comprehending the connectivity and operations within the nervous system.