CN I-VI

Question 1

CN I

Answer 1

Olfactory n.

Sensory - sense of smell from olfactory mucosa - caudal region of nasal cavity (SVA)

Nerves travel through cribriform plate to reach olfactory bulbs of telencephalon

Dysfunction: anosmia (absence of sense of smell)
Test: aromatic compounds to determine if sense is present

Question 2

CN II

Answer 2

Optic n.

Sensory - vision from rods and cones in nervous retina (SSA)
Right and left optic nn. travel through optic canals and cross at optic chiasma

Dysfunction: blindness (anopia)
Test: menace response; following an object; direct and consensual light reflexes

Question 3

CN III

Answer 3

Oculomotor n.

Motor (GSE) - extrinsic skeletal musculature
Dysfunction: lateral strabismus (deviation of eye) due to pull of lateral rectus; ptosis (drooping of superior palpebra)

Parasympathetic motor (GVE) - intrinsic smooth musculature
Dysfunction: mydriasis (dilation of pupil); cycloplegia (paralysis of accommodation)

Test: direct and consensual light reflexes

Question 4

CN IV

Answer 4

Trochlear n.

Motor - dorsal oblique m.

Only CN to exit dorsal surface of brain stem
Courses through orbital fissure to reach dorsal oblique m.

Dysfunction: eye rotates on anterior/posterior axis so that ventral part moves medially; difficult to evaluate in animals with round pupils

Question 5

CN V

Answer 5

Trigeminal n. (3 major branches)

Ophthalmic n. (sensory GSA)
Maxillary n. (sensory GSA)
Mandibular n. (sensory GSA, GP) (motor GSE-SVE)

Question 6

CN VI

Answer 6

Abducens n.

Motor - lateral rectus and retractor bulbi mm.
Nerve courses through orbital fissure to reach extrinsic ocular skeletal mm.

Dysfunction - medial strabismus due to pull of medial rectus m.