Summary of Cranial nerve functions
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
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 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.