Cranial Nerves: Functions & Course

CN I Olfactory: Type/function and structures innervated

- Special sensory (smell). Innervates the olfactory epithelium in the roof of the nasal cavity (superior concha, upper septum).

CN I Olfactory: Course through the head and neck

- Fibres pass up through the cribriform plate of the ethmoid to the olfactory bulb. The tract runs back along the underside of the frontal lobe. It does not attach to the brainstem.

CN II Optic: Type/function and structures innervated

- Special sensory (vision). Innervates the retina (ganglion cell axons).

CN II Optic: Course through the head and neck

- Leaves the orbit via the optic canal, meets its partner at the optic chiasm, then continues as the optic tract to the lateral geniculate nucleus.

- Technically an outgrowth of the diencephalon.

CN III Oculomotor: Type/function and structures innervated

- Somatic motor and parasympathetic.

- Motor: extraocular muscles

- Parasympathetic: sphincter pupillae and ciliary muscle (via the ciliary ganglion).

CN III Oculomotor: Course through the head and neck

- Exits the midbrain at the interpeduncular fossa, passes between the posterior cerebral and superior cerebellar arteries, runs in the lateral wall of the cavernous sinus, enters the orbit via the superior orbital fissure and splits into superior and inferior divisions.

CN IV Trochlear: Type/function and structures innervated

- Somatic motor. Innervates the superior oblique.

CN IV Trochlear: Course through the head and neck

- The only cranial nerve to exit the dorsal brainstem (midbrain) and the only one that fully decussates.

- Wraps around the cerebral peduncle, runs in the lateral wall of the cavernous sinus, enters the orbit via the superior orbital fissure.

CN V Trigeminal: Type/function and structures innervated

- Mixed (facial sensation and motor to muscles of mastication).

- Sensory: Face, cornea, nasal cavity and sinuses, teeth and gums, oral mucosa, general sensation of anterior two-thirds of tongue, dura.

- Motor (V3): muscles of mastication, tensor tympani and tensor veli palatini

CN V Trigeminal: Course through the head and neck

- Exits the lateral pons; trigeminal ganglion lies in Meckel's cave.

- V1 (ophthalmic): superior orbital fissure.

- V2 (maxillary): foramen rotundum, then pterygopalatine fossa and infraorbital canal.

- V3 (mandibular): foramen ovale into the infratemporal fossa (the only division carrying motor fibres).

CN VI Abducens: Type/function and structures innervated

- Somatic motor. Innervates the lateral rectus.

CN VI Abducens: Course through the head and neck

- Exits at the pontomedullary junction with a long intracranial course.

- Climbs over the petrous temporal apex, passes through the cavernous sinus (next to the internal carotid artery), enters the orbit via the superior orbital fissure.

CN VII Facial: Type/function and structures innervated

- Mixed (motor, taste, parasympathetic).

- Motor: muscles of facial expression, stapedius, stylohyoid, posterior belly of digastric.

- Taste: anterior two-thirds of tongue (via chorda tympani).

- Parasympathetic: salivary glands

- Sensory: small area of the external ear.

CN VII Facial: Course through the head and neck

- Exits at the pontomedullary junction (cerebellopontine angle) and enters the internal acoustic meatus with CN VIII.

- In the facial canal it passes the geniculate ganglion and gives off the greater petrosal nerve, nerve to stapedius and chorda tympani.

- Exits via the stylomastoid foramen, enters the parotid gland and divides

What are the terminal branches of CN VII Facial

Temporal, Zygomatic, Buccal, Marginal Mandibular, Cervical

CN VIII Vestibulocochlear: Type/function and structures innervated

- Special sensory (hearing and balance). Innervates the cochlea (hearing), semicircular canals, utricle and saccule (balance).

CN VIII Vestibulocochlear: Course through the head and neck

- Passes from the inner ear through the internal acoustic meatus to the pontomedullary junction (cerebellopontine angle).

CN IX Glossopharyngeal: Type/function and structures innervated

- Mixed.

- Motor: stylopharyngeus.

- Parasympathetic: parotid gland (via the otic ganglion).

- Sensory: posterior third of tongue (general sensation and taste), oropharynx, tonsil, middle ear, carotid sinus and body.

- Carries the sensory limb of the gag reflex.

CN IX Glossopharyngeal: Course through the head and neck

- Exits the medulla (post-olivary sulcus), leaves the skull via the jugular foramen, passes between the internal carotid artery and internal jugular vein, and curves forward around stylopharyngeus to reach the pharynx and tongue base.

CN X Vagus: Type/function and structures innervated

- Mixed.

- Motor: soft palate (except tensor veli palatini), pharynx (except stylopharyngeus), larynx.

- Parasympathetic: thoracic and abdominal viscera to the splenic flexure.

- Sensory: larynx and laryngopharynx, viscera, external ear and tympanic membrane, epiglottic taste buds.

CN X Vagus: Course through the head and neck

- Exits the medulla (post-olivary sulcus), leaves via the jugular foramen, and descends in the carotid sheath.

- Neck branches: pharyngeal, superior laryngeal (internal and external), recurrent laryngeal (right loops under the subclavian artery, left under the aortic arch), and cardiac. Continues into the thorax and abdomen.

CN XI Accessory: Type/function and structures innervated

- Somatic motor. Innervates sternocleidomastoid and trapezius (the cranial root is now usually regarded as part of the vagus).

CN XI Accessory: Course through the head and neck

- Spinal root arises from C1-C5/6, ascends through the foramen magnum, then exits via the jugular foramen.

- Descends, pierces and supplies sternocleidomastoid, crosses the posterior triangle superficially, and ends in trapezius.

CN XII Hypoglossal: Type/function and structures innervated

- Somatic motor. Innervates all intrinsic and extrinsic tongue muscles (genioglossus, hyoglossus, styloglossus) except palatoglossus (vagus). C1 fibres travelling with it supply geniohyoid and thyrohyoid.

CN XII Hypoglossal: Course through the head and neck

- Exits the medulla (pre-olivary sulcus) and leaves via the hypoglossal canal. Descends between the internal carotid artery and internal jugular vein, loops forward over the carotid arteries, passes deep to the posterior belly of digastric, and enters the floor of the mouth above the hyoid to reach the tongue.