Spinal Pathways Lecture Notes

Overview

• Focus on spinal pathways, specifically the tracts that ascend and descend in the spinal cord.
• Examines a transverse section of the spinal cord at level C8.

Spinal Cord Anatomy Recap

• Grey Matter: H-shaped, central part of the spinal cord.
• White Matter: Peripheral to grey matter, contains ascending and descending tracts.
• Dorsal Horns: Located at the back.
• Ventral Horns: Located anteriorly.
• Central Canal: Located in the center.
• Dorsal Median Sulcus: Located dorsally.
• Ventral Median Fissure: Located ventrally.

Tracts and Fasciculi

• Fasciculi: Bundles of axons, either ascending (sensory) or descending (motor).
• Ascending tracts carry sensory information to the brain.
• Descending tracts carry motor information from the brain to the periphery.

Ascending Tracts

• Carry various sensory modalities:
  • Pain
  • Temperature
  • Tactile information (coarse to fine touch)
  • Vibration
  • Muscle and joint receptor information
• Conscious vs. Subconscious Processing
  • Consciously processed information is sent to the cerebral cortex.
  • Subconsciously processed information, like proprioceptive data, goes to other brain areas such as the cerebellum.

Neuron Pathways

• Three Neuron Sequence for consciously processed information:
  • First Order Neuron: Primary afferent, ipsilateral, cell bodies in the dorsal root ganglion.
    • Terminates by forming a synapse in the dorsal horn of grey matter or in the medulla oblongata.
  • Second Order Neuron: Crosses over (decussates) to the other side and ascends to the thalamus.
  • Third Order Neuron: Cell body in thalamus, projects to the somatosensory cortex, where sensation is perceived.

Important Terms

• Ipsilateral: Same side.
• Contralateral: Opposite side, used to describe the path after decussation.
• Decussation: Crossing over of the second-order neuron to the opposite side.

Next Steps

• Further examination of ascending and descending tracts within the spinal cord.