Somatosensory Tracts

Introduction

• Somatosensory: Relates to the senses of the body.
• Tracts: Collections of axons traveling through the central nervous system (CNS).
• Different types of somatosensory information travel in specific pathways in the CNS.

Categories of Somatosensation

1. Position, Vibration, Fine Touch Sense
   • Highly precise sensory information.
2. Pain, Temperature, Gross Touch Sense
   • Less precise sensory information.

Pathways of Somatosensory Information

• Peripheral Nervous System: Information travels from the body to the CNS via spinal nerves.
• Spinal Cord: Acts as a conduit for somatosensory information.

Specific Pathway Examples

• Position Sense from Arm:
  • Detected by receptors and travels through peripheral and spinal nerves into the spinal cord.
• Pain Sense from Leg:
  • Detected by receptors, travels similarly through nerves into the spinal cord.

Head and Face Somatosensation

• Information enters the brain stem through cranial nerves instead of the spinal cord.
• Examples:
  • Vibration from the Face: Travels via cranial nerves into the brain stem.
  • Temperature Sense from Face: Follows a similar path through cranial nerves.

CNS Processing

• Spinal Cord and Brain Stem: Initial integration of somatosensory information.
• Somatosensory Tracts:
  • Specific tracts carry sensory information upwards, crossing over to the opposite side of the CNS.

Pain, Temperature, and Gross Touch Sense

• Enters spinal cord, crosses to the opposite side, travels upwards through spinal cord and brain stem, reaching deep in the cerebrum.

Position, Vibration, and Fine Touch Sense

• Enters higher in the spinal cord, crosses higher in the brain stem, and travels similarly to deep cerebrum.

Integration in the Brain

• Cerebral Hemisphere: All types of somatosensory information converge in one area.
• Cortex Processing: Further processing in outer areas of the cerebral hemisphere.

Consequences of CNS Injury

• Crossed Pathways: Injury in one cerebral hemisphere can lead to sensory loss on the opposite side of the body.
• Specificity: Different pathways may lead to selective sensory losses, depending on the affected CNS region.

Conclusion

• Understanding somatosensory tracts is crucial for interpreting sensory deficits.
• Injuries to the CNS have predictable effects due to the structure of somatosensory pathways.