Sensory Function and Testing

• Sensory abilities include touch, pain, temperature, and proprioception (body position awareness).
• Loss of sensation indicates damage to nerve pathways.

Dermatomes and Nerve Pathways

• Dermatomes: Map of skin regions supplied by specific spinal nerves.
• Sensory information travels via a three-neuron pathway:
  1. Peripheral nerve (detects stimulus).
  2. Spinal cord or brainstem (via dorsal columns or spinothalamic tracts).
  3. Somatosensory cortex in the parietal lobe (interprets sensation).

Causes of Sensory Loss and Recovery

• Damage to peripheral nerves:
  • Often regrows over months (e.g., sports injury).
  • Leads to localized sensory deficits (e.g., in the finger).
• Damage to spinal cord or brain:
  • Less likely to regenerate.
  • Leads to more extensive deficits.

Cranial Nerves and Sensory Functions

• Cranial nerves carry sensory info from the face, eyes, nose, mouth, and ears.
• Damage clues:
  • Loss of smell → Cranial nerve 1 (olfactory).
  • Loss of vision → Cranial nerve 2 (optic nerve).
  • Inability to move eyes → Cranial nerves 3, 4, and 6.
  • Loss of sensation in face → Cranial nerve 5 (trigeminal).
  • Dizziness or vertigo and loss of hearing → Cranial nerve 8 (vestibulocochlear).

Facial Movement and Cranial Nerve Motor Functions

• Facial expression:
  • Cranial nerve 7 (facial nerve).
• Swallowing and tongue movement:
  • Cranial nerves 9 (glossopharyngeal) and 12 (hypoglossal).
• Shoulder elevation:
  • Cranial nerve 11 (accessory).
• Taste:
  • Cranial nerve 9 (glossopharyngeal).

Monitoring Nerve Function

• Electrode testing:
  • Measure impulses traveling down nerves.
  • Damage to myelin sheath impairs impulse conduction but may recover.

Summary

• Sensory and motor deficits clues to specific cranial nerve injuries.
• Damage can be localized or widespread depending on the neural pathway affected.
• Clinical tests and imaging help determine extent and location.