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Cranial Nerves
Functional groups
Somatomotor set
- CNs 3, 4, 6, 12, and 11 are part of the somatomotor set.
- They all innervate midline musculature and have midline-lying nuclei.
Solely special sensory set
- CNs 1, 2, 8 are the solely special sensory set.
- These CNs purely serve sensory function.
Pharyngeal arch set
- CNs 5, 7, 9, 10 are the pharyngeal arch set.
- These nerves all contain numerous functions.
Somatomotor Set
CN 3, oculomotor nerve:
- Exits the midbrain near midline; midline brainstem strokes often injure this nerve.
- It innervates several ocular muscles, which are the following extraocular recti muscles: medial, superior, and inferior; it innervates the inferior oblique and levator palpebrae muscles; and it produces pupillary constriction; thus, it serves 4 of the 6 primary eye movements and constricts the pupils.
- Clinical Correlation: 3rd Nerve Palsy
- Wraps around the outside of the pons (even though it originates from midline of the lower midbrain).
- CN 4 decussates (crosses midline) as it exits the brainstem contralateral (on the side opposite) to its side of origin – it's the only CN to make this decussation.
- It innervates the superior oblique, which provides intorsion and depression. If someone has a head tilt, it may be to bring their eyes into alignment from a CN 4 injury.
- Clinical Correlation: 4th Nerve Palsy
- Exits near midline from the pontomedullary junction.
- It innervates the lateral rectus, which rotates the eye outward.
- Clinical Correlation: 6th Nerve Palsy
- Emerges paracentrally from the mid-medullary level.
- Just like CNs 3 and 6, CN 12 has a central (midline) course.
- It provides tongue protrusion.
- Emerges laterally from the cervical spinal cord.
- CN 11 is no longer thought to have additional brainstem origins.
- It provides head turn and shoulder shrug.
- Raise your shoulder and feel the action of trapezius, which it innervates.
Solely Special Sensory Set
CN 1, olfactory nerve
- Serves our sense of smell.
- The olfactory nerve is the short course of olfactory wiring from olfactory epithelial surface to the olfactory bulb.
- Functions in vision.
- It's thick because of how much wiring is devoted to vision – most of the posterior brain solely deals with visual processing!
- The pituitary gland can grow into and injure the optic chiasm.
- Carries hearing (auditory) and balance (sensory) – two separate sensory functions.
Pharyngeal Arch Set
CN 5, trigeminal nerve
- Provides motor innervation for mastication (chewing).
- Receives facial sensation.
- The sensory portion of CN 5 is thick due to the sensitivity of facial sensation.
- Provides facial movement
- Provides taste sensation from the anterior two-thirds of the tongue.
- Facial palsy (droop), which is flattening of one side of the face is a common presenting neurologic complaint.
- Learn them together because their actions are similar and most easily remembered when grouped.
As a simplification, both CNs are involved:
- Swallow
- Cardio-pulmonary function
- CN 9 is involved in salivation
- CN 10 is involved in gut motility.
- CNs 9 and 10 are carry key autonomic functions.
Mneomnic
On Old Olympus's Towering Top, A Finn And German Viewed Some Hops.
CN 1 – Olfactory (On)
CN 2 – Optic (Old)
CN 3 – Oculomotor (Olympus)
CN 4 – Trochlear (Towering)
CN 5 – Trigeminal (Tops)
CN 6 – Abducens (A)
CN 7 – Facial (Finn)
CN 8 – Auditory or Vestibular (aka vestibulocochlear nerve).
CN 9 – Glossopharyngeal (German)
CN 10 – Vagus (Viewed)
CN 11 – Spinal accessory (Some)
CN 12 – Hypoglossal (Hops)