What are the 12 cranial nerves, their functions, and the base of skull fossa they pass through?

The 12 Cranial Nerves: Functions and Skull Base Foramina

The 12 cranial nerves emerge from specific regions of the brain and pass through distinct foramina at the skull base, each serving specialized sensory and motor functions essential for head and neck innervation. 1, 2

Detailed Overview of the 12 Cranial Nerves

Anterior Cranial Fossa

1. CN I (Olfactory Nerve)

   • Function: Special sensory - smell
   • Passes through: Cribriform plate of ethmoid bone
   • Note: Not a true nerve but a tract formed from the telencephalon 1

2. CN II (Optic Nerve)

   • Function: Special sensory - vision
   • Passes through: Optic canal
   • Note: Actually a tract formed from the diencephalon, not a true nerve 1

Middle Cranial Fossa

1. CN III (Oculomotor Nerve)

   • Function:
     • Somatic motor - controls most extraocular muscles (superior, medial, inferior recti, inferior oblique)
     • Visceral motor - pupillary constriction, accommodation
   • Passes through: Superior orbital fissure

2. CN IV (Trochlear Nerve)

   • Function: Somatic motor - innervates superior oblique muscle
   • Passes through: Superior orbital fissure
   • Note: Only cranial nerve that exits from dorsal aspect of brainstem

3. CN V (Trigeminal Nerve)

   • Function: General sensory to face, oral cavity, nasal cavity; motor to muscles of mastication 2
   • Divisions:
     • V1 (Ophthalmic) - Passes through superior orbital fissure
     • V2 (Maxillary) - Passes through foramen rotundum
     • V3 (Mandibular) - Passes through foramen ovale

4. CN VI (Abducens Nerve)

   • Function: Somatic motor - innervates lateral rectus muscle
   • Passes through: Superior orbital fissure

Posterior Cranial Fossa

1. CN VII (Facial Nerve)

   • Function:
     • Branchial motor - facial expression muscles
     • Special sensory - taste (anterior 2/3 of tongue)
     • Visceral motor - lacrimal, submandibular, sublingual glands 2
   • Passes through: Internal acoustic meatus → facial canal → stylomastoid foramen

2. CN VIII (Vestibulocochlear Nerve)

   • Function: Special sensory - hearing and balance
   • Passes through: Internal acoustic meatus
   • Divisions:
     • Vestibular branch - balance
     • Cochlear branch - hearing

3. CN IX (Glossopharyngeal Nerve)

   • Function:
     • Branchial motor - stylopharyngeus muscle
     • Special sensory - taste (posterior 1/3 of tongue)
     • General sensory - pharynx
     • Visceral motor - parotid gland 2
   • Passes through: Jugular foramen

4. CN X (Vagus Nerve)

   • Function:
     • Branchial motor - palatal and pharyngeal muscles
     • Visceral motor - thoracic and abdominal viscera
     • General sensory - pharynx, larynx, viscera 2
   • Passes through: Jugular foramen
   • Note: Imaging should extend to mid-thorax (aortic pulmonary window) 2

5. CN XI (Spinal Accessory Nerve)

   • Function: Branchial motor - sternocleidomastoid and trapezius muscles 2
   • Passes through: Jugular foramen
   • Note: Cranial root joins vagus nerve; spinal root innervates SCM and trapezius

6. CN XII (Hypoglossal Nerve)

   • Function: Somatic motor - intrinsic and extrinsic tongue muscles 2
   • Passes through: Hypoglossal canal

Clinical Significance and Imaging

• MRI is the gold standard for evaluating cranial nerves, providing excellent soft-tissue resolution 2
• CT is superior for evaluating bony foramina and skull base structures 2
• The styloid diaphragm divides the infratemporal fossa into prestyloid and retrostyloid regions, with the latter containing CN IX-XII and major vessels 3
• Cranial nerve identification during skull base surgery is crucial to prevent intraoperative damage 4

Common Anatomical Relationships

• The glossopharyngeal nerve (CN IX) is typically found posterior and lateral to the stylopharyngeus muscle 3
• The vagus nerve (CN X) is consistently found in the angle formed posteriorly by the internal carotid artery and internal jugular vein 3
• The hypoglossal nerve (CN XII) can be identified as it crosses under the sternocleidomastoid branch of the occipital artery, approximately 25 mm posterior to the angle of the mandible 3

Potential Compression Points

Two groups of compression points may lead to cranial nerve dysfunction 5:

• Medial line: Brain stem points, usually at nerve root entry/exit zones
• Lateral line: Skull eminences where nerves lie, or skull and dural foramina through which they exit

Understanding these anatomical relationships is essential for accurate diagnosis of cranial neuropathies and for safe surgical approaches to the skull base.