The OD's Practical Guide to Cranial Nerves: Downloadable Cheat Sheet

A neurological exam is an important tool in a patient assessment and having a firm handle on neurological concepts and terminology is key. Optometrists should evaluate cranial nerves if they suspect underlying etiologies like stroke, lesions, demyelinating disease, head trauma, or Bell’s palsy. Ocular findings such as double vision, ptosis, pupil abnormalities, and vision loss may also come up as red flags.

Download the OD's Practical Guide to Cranial Nerves cheat sheet for a handy table + mnemonics!

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Get the cranial nerves cheat sheet!

Download the cheat sheet for easy reference to cranial nerves I - XI, plus handy mnemonics!

Remember: cranial nerves can be afferent, efferent, or both

Let’s start off with a simple anatomy of the brain to help guide us in learning the positions of these nerves. Cranial nerves originate from the brain or brainstem. They are numbered from where they emerge: front to back. They can be either afferent (sensory), efferent (motor), or sometimes both! Let’s get started . . .

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CNI - Olfactory

Origination: Cerebrum (1 of 2 nerves that originates from the cerebrum)
Purpose: Olfaction (sense of smell)
Innervation: Sensory
Test: Smell some coffee beans (try not to be too adventurous with smelling funny things, pee-yew!)

Your typical patient workup will have already covered testing for CNII, III, IV, and VI.

CNII - Optic

Origination: Cerebrum (the only other nerve that originates from there)
Purpose: vision (our favorite!)
Innervation: Sensory
Test: CVF, Snellen VA

CNIII - Oculomotor

Origination: Midbrain
Purpose: Eye movement, pupillary constriction, accommodation
Divisions:
- Superior: levator palpebrae (lid elevation), superior rectus
- Inferior: inferior rectus, medial rectus, inferior oblique, ciliary ganglion (sphincter pupillae, ciliary muscles)
Innervation: Motor
Test: PERRLA, EOM

Tidbit: CNIII palsy will present as a down and out eye with a ptosis. Pupil may be dilated (involved), or normal (spared).

CNIV - Trochlear

Origination: Midbrain
Purpose: Eye movement with the superior oblique
Innervation: Motor
Test: EOM

Tidbit #1: Palsy of this muscle causes hypertropia and a torsional component. Pt will have a head tilt opposite to the side of palsy.

Tidbit #2: Something unique about this nerve is that it is the ONLY cranial nerve that leaves the nervous system dorsally.

Tidbit #3: Also skinniest nerve with the longest intracranial course, which is why it is the most prone to trauma.

CNV - Trigeminal

Origination: Pons
Purpose: Corneal and facial sensation, mastication
Branches: (“Tri”-geminal meaning 3 branches!)
- V1: Ophthalmic (nasociliary, frontal, and lacrimal)
- V2: Maxillary (infraorbital, and zygomatic)
- V3: Mandibular
Innervation: Both
Test: Compare sensation from forehead, upper cheek, and jaw. Clench teeth and feel masseter muscle. Open mouth, and check resistance to closing jaw.

CNVI - Abducens

Origination: Pontomedullary region
Purpose: Eye movement with the lateral rectus (abduct!)
Innervation: Motor
Test: EOM

Tidbit: Hallmark sign is a horizontal diplopia, greater at distance, with an abduction deficit. It is the most common ischemic vascular palsy.

CNVII - Facial

Origination: Pontomedullary region
Purpose: Facial expression, taste, anterior ⅔ of tongue, lacrimation, and salivation
Branches: (from superior to inferior)
- Posterior auricular branch
- Temporal branches
- Zygomatic branches
- Buccal branches
- Mandibular branches
- Cervical branches
Mnemonic: Party to Zanzibar by motor car! Try using your hand to imagine the distribution.

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Innervation: Both
Test: Smile, frown, puff out cheeks. Close eyes shut.

Tidbit: 7th nerve palsy is also known as Bell’s palsy.

CNVIII - Vestibulocochlear

Origination: Pontomedullary region
Purpose: Hearing and equilibrium (just like how the name sounds)
Innervation: Sensory
Test: Make light sound next to each ear

CNIX - Glossopharyngeal

Glosso (tongue), pharyn (throat) geal

Origination: Medulla oblongata
Purpose: Taste, posterior ⅓ of tongue, swallowing, salivation, and sensory information from the carotid sinus.
Innervation: Both, at the pharynx
Test: Say aaaaAaaa and uvula should move up. Check gag reflex.

CNX - Vagus

Origination: Medulla oblongata
Purpose: Taste, swallowing, palate elevation, speech, slowing heart rate
Innervation: Both
Test: Assess speech and swallow.

Tidbit: It is the longest nerve. Think “vandering”.

CNXI - Accessory

Origination: Medulla oblongata and cervical spinal cord
Purpose: Head turning and shoulder shrugging
Innervation: Motor, at the trapezius and sternocleidomastoid muscle
Test: Move head side to side, up and down. Shrug shoulders.

CNXII - Hypoglossal

Hypo (under), glossal (tongue)

Origination: Medulla oblongata
Purpose: Tongue movement
Innervation: Motor

Test: Move tongue side to side