Table of contents · 7 sections
The 12 cranial nerves are a fundamental topic in neurology and anatomy, essential for performing a neurological examination. Each nerve has a unique course, nuclei, and clinical presentation when damaged. This article provides a comprehensive table, mnemonics, and clinical correlations for exams and clinical practice.
Overview table of the 12 cranial nerves
| № | Name | Type | Function | Skull exit |
|---|---|---|---|---|
| I | Olfactory (n. olfactorius) | Sensory | Smell | Cribriform plate |
| II | Optic (n. opticus) | Sensory | Vision | Optic canal |
| III | Oculomotor (n. oculomotorius) | Motor + parasympathetic | Eye movements (4 of 6 muscles), eyelid elevation, pupillary constriction, accommodation | Superior orbital fissure |
| IV | Trochlear (n. trochlearis) | Motor | Superior oblique muscle (gaze down and in) | Superior orbital fissure |
| V | Trigeminal (n. trigeminus) | Mixed | Facial sensation (V1, V2, V3) + muscles of mastication (V3) | V1 — superior orbital fissure, V2 — foramen rotundum, V3 — foramen ovale |
| VI | Abducens (n. abducens) | Motor | Lateral rectus muscle (eye abduction) | Superior orbital fissure |
| VII | Facial (n. facialis) | Mixed | Muscles of facial expression, taste (anterior 2/3 of tongue), lacrimal and submandibular/sublingual glands | Internal acoustic meatus → stylomastoid foramen |
| VIII | Vestibulocochlear (n. vestibulocochlearis) | Sensory | Hearing and balance | Internal acoustic meatus |
| IX | Glossopharyngeal (n. glossopharyngeus) | Mixed | Taste (posterior 1/3 of tongue), gag reflex, carotid sinus, parotid gland | Jugular foramen |
| X | Vagus (n. vagus) | Mixed | Parasympathetic innervation of viscera up to the splenic flexure, larynx, pharynx | Jugular foramen |
| XI | Accessory (n. accessorius) | Motor | Sternocleidomastoid and trapezius muscles | Jugular foramen |
| XII | Hypoglossal (n. hypoglossus) | Motor | Muscles of the tongue | Hypoglossal canal |
Mnemonics for memorization
Nerve order: "Oh, Oh, Oh, To Touch And Feel Very Good Velvet, AH!" (Olfactory, Optic, Oculomotor, Trochlear, Trigeminal, Abducens, Facial, Vestibulocochlear, Glossopharyngeal, Vagus, Accessory, Hypoglossal)
Nerve type (S — sensory, M — motor, B — mixed): "Some Say Marry Money, But My Brother Says Big Brains Matter More" → S, S, M, M, B, M, B, S, B, B, M, M
Ocular motor nerves (III, IV, VI)
These three nerves control eye movements:
- III (oculomotor) — all muscles EXCEPT superior oblique and lateral rectus + m. levator palpebrae + parasympathetics (miosis, accommodation)
- IV (trochlear) — superior oblique (SO) only. Mnemonic: SO₄ (sulfate formula = 4th nerve → superior oblique)
- VI (abducens) — lateral rectus (LR) only. Mnemonic: LR₆ (6th nerve → lateral rectus)
Formula: LR₆SO₄R₃ — lateral rectus (VI), superior oblique (IV), all others (III).
Trigeminal nerve (V): three branches
| Branch | Innervation area | Clinical notes |
|---|---|---|
| V1 (ophthalmic) | Forehead, upper eyelid, nasal dorsum, cornea | Corneal reflex (afferent limb — V1, efferent — VII) |
| V2 (maxillary) | Cheek, upper lip, upper teeth, nasal ala | Trigeminal neuralgia frequently involves V2 and/or V3 |
| V3 (mandibular) | Mandible, lower teeth, anterior 2/3 of the tongue (sensation!) + muscles of mastication | The only branch with a motor component |
Facial nerve (VII): topical diagnosis
The facial nerve carries 5 components, and the level of the lesion determines the clinical presentation:
- Central paresis (supra-nuclear lesion) — weakness of the lower face only on the contralateral side (forehead is spared due to bilateral cortical innervation)
- Peripheral paresis (nuclear or nerve lesion) — weakness of the entire half of the face on the ipsilateral side
- Lesion within the temporal bone canal → + hyperacusis (involvement of n. stapedius), + taste disturbance (chorda tympani), + dry eye (n. petrosus major)
Bell's palsy — idiopathic peripheral paresis of the VII nerve. Acute onset, unilateral, treatment — GCS within the first 72 hours.
Vagus nerve (X): the longest cranial nerve
- Parasympathetic innervation of the heart, lungs, and GI tract up to the splenic flexure
- Superior laryngeal nerve — external branch innervates the cricothyroid muscle (tension of vocal folds). Injury during thyroid surgery → "tired voice"
- Recurrent laryngeal nerve — all other laryngeal muscles. Left loops around the aortic arch, right — subclavian artery. Injury → hoarseness (unilateral paresis) or stridor (bilateral)
Frequently asked questions
How to distinguish central from peripheral facial nerve (VII) paresis?
Central (stroke): only the lower facial expression muscles are affected contralaterally — the patient can wrinkle the forehead and close the eyes. Peripheral (Bell's palsy): the entire half of the face is affected ipsilaterally — inability to wrinkle the forehead, close the eye, positive Bell's phenomenon (eyebrow/eyeball rolls upward upon attempted eye closure).
Why does the tongue deviate towards the side of the lesion in hypoglossal (XII) nerve injury?
The hypoglossal nerve innervates the genioglossus muscle, which protrudes the tongue forward and to the opposite side. In a unilateral lesion, the paralyzed side cannot "push" the tongue — the healthy side dominates and pushes it toward the side of the lesion. Mnemonic: "the tongue licks the wound" — points to the affected side.
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