Examination of Cranial Nerves

Anatomy and function:

There are twelve pairs of cranial nerves. Cranial nerve I is a fiber tract emerging from the brain directly, while cranial nerves II through XII arise from the diencephalon and brain stem. With a thorough understanding of normal cranial nerve function and testing, the examiner can localize lesions when abnormalities are found. For example, if there is facial weakness in a patient with hemiplegia, lateralization (determining whether the facial weakness is on the ipsilateral or contralateral side) will help determine the level of the lesion. Similarly, characterizing facial weakness will help differentiate upper and lower motor neuron patterns.

The following tables outline cranial nerve function and methods of evaluation.

Cranial Nerve	Function
I. Olfactory	Sense of smell
II. Optic	Vision
III. Oculomotor	Pupillary constriction, opening eyes, some extraocular movements
IV. Trochlear	Downward, inward movement of eye
V. Trigeminal	Motor - temporal and masseter muscles (jaw clenching), lateral movement of jaw Sensory - Three divisions: (1) ophthalmic, (2) maxillary, (3) mandibular
VI. Abducens	Lateral deviation of eye
VII. Facial	Motor - facial movements (facial expression, closing eye, closing mouth)
VIII. Acoustic	Hearing (cochlear division) and balance (vestibular division)
IX. Glossopharyngeal	Motor - pharynx Sensory - posterior portions of eardrum and ear canal, pharynx, and posterior tongue, including taste (salty, sweet, sour, bitter)
X. Vagus	Motor - palate, pharynx, and larynx Sensory - pharynx and larynx
XI. Spinal accessory	Motor - the sternomastoid and upper portion of trapezius
XII. Hypoglossal	Motor - tongue

Cranial Nerve	Evaluation
I.	Test each nostril separately, have patient sniff and identify common odor (soap, coffee, lemon)
II.	Evaluate optic nerve, visual fields, visual acuity, pupil response to light (afferent CN II)
II, III.	Pupillary size and reaction to light (direct and consensual response)
III, IV, VI.	Evaluate extraocular movements (evaluate for conjugate movement, weakness of individual muscle, nystagmus); evaluate convergence reflex
V.	Evaluate corneal reflexes, sensation in V1, V2, V3, temporalis and masseter muscle strength, jaw jerk
VII.	Test strength of muscles of facial expression; can test sweet taste on anterior tongue
VIII.	Evaluate hearing, compare bone and air conduction and test for lateralization of sound
IX, X.	Evaluate gag reflex, elevation of palate with "Ah"; quality of voice
XI.	Test strength of trapezius and sternomastoid muscle
XII.	Evaluate tongue for atrophy, fasciculations, fibrillations, symmetry, deviation,strength

Examination techniques:

Click on the video icon to view a demonstration of the cranial nerve exam.