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Cranial nerve testing (Proceedings)

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Oct 01, 2008

Summary of Cranial nerve functions

CN I-olfactory-Smell

CN II-optic-Vision and pupillary light reflexes

CN III-oculomotor-1) Medial (primarily) movement of the eye through innervation of the extaocular muscles, 2) Pupillary constriction through parasympathetic innervation of the iris

CN IV-trochlear: Extorion of the eye through innervation of the dorsal oblique extraocular muscle

CN V-trigeminal-1) Sensation to the eye and cornea 2) Sensation to the maxillary area, 3) Motor innervation to the muscle of mastication

CN VI-abducens-Innervation to the lateral rectus and retractor bulbi extraocular muscles

CN VII-facial-1) Motor to the muscles of facial expression, 2) Taste, 3) Salivation/lacrimation, 4) Skin sensation (ear)

CN VII-vestibulocochlear-1) Balance and posture 2) Hearing

CN IX-glossopharyngeal-1) Motor and sensation to pharynx, 2) Taste, 3) Salivation

CN X-vagus-1) Motor and sensation to larynx, 2) Taste, 3) Salivation, 4) Parasympathetic innervation to viscera

CN XI-accessory-Motor to trapezius muscle

CN XII-hypoglossal-Motor to the tongue

CN Testing

CN 1: Olfactory N: Not routinely tested.

CN 2: Optic N: Observing movement of the animal in the room and assessing its ability to follow objects evaluate vision. If in doubt, throw a cotton ball in the animal's visual field and see if he follows it with his eyes. Making a menacing gesture towards the animal's eye performs the menace response; look for a blink. Pupillary light reflexes are evaluated with a bright light and looking for both direct and consensual responses.

CN 3: Oculomotor N: The parasympathetic component of CN III is evaluated with pupillary light reflexes. CN III dysfunction causes a ventrolateral strabismus due to paralysis of the majority of the extraocular muscles; ptosis due to paralysis of the levator palpebrae muscle; mydriasis and unresponsive pupil due to paralysis of the iris muscle, and reduced or asymmetrical eyeball movements when testing physiological nystagmus in vertical and horizontal planes.

CN 4: Trochlear N: CN IV dysfunction causes lateral deviation of the superior retinal vein on ophthalmoscopic exam in the dog (round pupil), and lateral deviation of the dorsal aspect of the pupil in the cat (vertical pupil).

CN 3, 4, and 6: They are usually evaluated together by observing eye movement in all planes. CN 6: Abducens N: CN VI dysfunction causes medial strabismus of the eyeball and reduced or symmetrical movements of the eyeball when testing physiological nystagmus in the horizontal plane. Note that it can be tested with the "Corneal reflex" described under CN 5.