Medicine & USMLE

Olfactory Nerve (CN I)

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Cranial Nerves
  1. Olfactory Nerve (CN I)
  2. Optic Nerve (CN II)
  3. Oculomotor Nerve (CN III)
  4. Trochlear Nerve (CN IV)
  5. Trigeminal Nerve (CN V)
  6. Abducens Nerve (CN VI)
  7. Facial Nerve (CN VII)
  8. Vestibulocochlear Nerve (CN VIII)
  9. Glossopharyngeal Nerve (CN IX)
  10. Vagus Nerve (CN X)
  11. Accessory Nerve (CN XI)
  12. Hypoglossal Nerve (CN XII)

Summary

The olfactory nerve, also known as cranial nerve number I or the first cranial nerve, is a sensory nerve that is responsible for carrying our sense of smell. The nerve endings of the olfactory nerve start in the mucosal walls of our nose, pass through the cribriform plate of our skull, and end in the olfactory bulb of our forebrain, which then processes smell before sending it to other parts of the brain. Uniquely, the olfactory nerve is the only cranial nerve that does not transmit signals using a thalamic relay, opting instead to send signals directly to the cortex and other parts of the brain.

Key Points

  • Olfactory Nerve (Cranial Nerve I)
    • Nerve Type
      • Sensory
    • Function
      • Smell
        • Test function with scents (eg. cinnamon, coffee, clove)
    • Nerve entry/exit
      • Does not originate from or travel to brainstem nuclei
    • Cranial foramen
      • Cribriform plate
        • Axons from olfactory mucosa in nasal cavity travel through cribriform plate to reach olfactory bulb, which transmits information to the brain
        • Can be damaged in high force trauma or nasal fractures
    • Other information
      • Only cranial nerve with no thalamic relay to the cortex
        • Olfactory bulb transmits directly to cortex or other structures such as amygdala and hippocampus