Cranial Nerves Overview Twelve pairs of nerves originating from the brain; numbered I–XII using Roman numerals. Origin of Cranial Nerves First two pairs (I–II) arise from forebrain; remaining pairs (III–XII) arise from brainstem. Function of Cranial Nerves Primarily serve head and neck structures; one exception (vagus nerve) extends into thoracic and abdominal cavities. Cranial Nerve Numbering Begin anteriorly and move posteriorly along the inferior surface of the brain. Cranial Nerve Naming Names reflect location, innervation, or function. Mnemonic for Cranial Nerve Names Olfactory, Optic, Oculomotor, Trochlear, Trigeminal, Abducens, Facial, Vestibulocochlear, Glossopharyngeal, Vagus, Accessory, Hypoglossal. Fun Mnemonic Phrase (Names) On Occasion Our Trusty Truck Acts Funny — Very Good Vehicle Any How. Mnemonic for Cranial Nerve Functions (Sensory/Motor/Both) Some Say Marry Money But My Brother Says Bad Business Marry Money. CN I: Olfactory Nerve Sensory; responsible for sense of smell; passes through cribriform plate of ethmoid bone. CN II: Optic Nerve Sensory; responsible for vision; exits through optic canal (optic foramen). CN III: Oculomotor Nerve Motor; controls most eye movements and pupil constriction; exits through superior orbital fissure. Oculomotor Somatic Function Controls superior rectus, inferior rectus, medial rectus, and inferior oblique eye muscles. Oculomotor Autonomic Function Controls sphincter pupillae muscle for pupil constriction. CN IV: Trochlear Nerve Motor; controls superior oblique muscle of the eye; exits through superior orbital fissure. Trochlear Function Allows eye to move inferolaterally (downward and outward). CN V: Trigeminal Nerve Both sensory and motor; major sensory nerve of the face with three divisions (V1, V2, V3). Trigeminal Divisions V1 Ophthalmic (superior orbital fissure), V2 Maxillary (foramen rotundum), V3 Mandibular (foramen ovale). Trigeminal Function Sensory input from face, scalp, teeth, and anterior tongue; motor control of muscles of mastication. CN VI: Abducens Nerve Motor; controls lateral rectus muscle of the eye for lateral movement; exits through superior orbital fissure. Eye Movement Coordination Controlled by oculomotor (III), trochlear (IV), and abducens (VI) nerves. Abducens Palsy Results in inability to move eye laterally (damage to lateral rectus muscle). Trochlear Palsy Causes weakness in downward eye movement; patient may tilt head to compensate. Oculomotor Palsy Causes drooping eyelid (ptosis), dilated pupil, and inability to move eye upward, downward, or inward. CN VII: Facial Nerve Both sensory and motor; innervates muscles of facial expression and taste from anterior two-thirds of tongue. Branches of Facial Nerve Five branches: Temporal, Zygomatic, Buccal, Mandibular, and Cervical. Facial Nerve Function Motor control of facial muscles, secretion from salivary and lacrimal glands, and taste sensation. CN VIII: Vestibulocochlear Nerve Sensory; responsible for equilibrium (vestibular branch) and hearing (cochlear branch). Vestibulocochlear Function Transmits sound and balance information from inner ear to brain. CN IX: Glossopharyngeal Nerve Both sensory and motor; innervates pharynx and posterior tongue. Glossopharyngeal Functions Controls swallowing, taste on posterior one-third of tongue, and salivary gland secretion. CN X: Vagus Nerve Both sensory and motor; only cranial nerve extending beyond head and neck into thorax and abdomen. Vagus Nerve Function Regulates heart rate, breathing, digestive activity, and contributes to swallowing and voice production. Vagus Sensory Component Provides visceral sensation and taste from epiglottis and pharynx. CN XI: Accessory Nerve Motor; controls muscles of the larynx, pharynx, and neck; assists in head and shoulder movement. Accessory Nerve Function Innervates sternocleidomastoid and trapezius muscles for head rotation and shoulder elevation. CN XII: Hypoglossal Nerve Motor; controls tongue movements for chewing, swallowing, and speech. Hypoglossal Function Allows food mixing, manipulation, and articulation during speech. Cranial Nerve Functional Summary Sensory: I, II, VIII. Motor: III, IV, VI, XI, XII. Both: V, VII, IX, X. Cranial Nerve Function Mnemonic I–Sensory, II–Sensory, III–Motor, IV–Motor, V–Both, VI–Motor, VII–Both, VIII–Sensory, IX–Both, X–Both, XI–Motor, XII–Motor. Cranial Nerve Testing Used clinically to identify brainstem lesions, neuropathies, or localized nerve damage. Clinical Importance of Cranial Nerves Critical for assessing neurological health and localizing brain or skull base disorders.
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