Cranial Nerves

Question 1

CN 1

• Name
• Function
• Clinical test
• Signs of dysfunction

Answer 1

• Name = Olfactorius
• Function = Smell
• Clinical test = Not routinely tested (Smell food, interest in food)
• Signs of dysfunction = Anosia; hyponosia

Question 2

CN 2

• Name
• Function
• Clinical test
• Signs of dysfunction

Answer 2

• Name = Opticus
• Function = Vision; response to light
• Clinical test = Menace response; PLR; obstacle course; tracking moving objects
• Signs of dysfunction = Blindness; dilated, diminished to absent PLRs

Question 3

CN 3

• Name
• Function
• Clinical test
• Signs of dysfunction

Answer 3

• Name = Oculomotorius
• Function = Motor to extraocular muscles; parasympathetic to pupil (pupil constriction)
• Clinical test = Physiologic nystagmus; resting eyeball position; PLRs
• Signs of dysfunction = Ventrolateral strabismus; ptosis (dropped eyelid); dilated pupils; diminished to absent PLRs

Question 4

CN 4

• Name
• Function
• Clinical test
• Signs of dysfunction

Answer 4

• Name = Trochlearis
• Function = Motor to dorsal oblique muscle
• Clinical test = Resting eyeball position (easily observed in cats; fundic examination needed to discern in dogs)
• Signs of dysfunction = Extorsion of the globe; dorsomedial strabismus (cat); lateral deviation of retinal vein (dog)

Question 5

CN 5

• Name
• Function
• Clinical test
• Signs of dysfunction

Answer 5

• Name = Trigeminus
• Function = Motor to muscles of mastication (mandibular); sensory to face (ophthalmic, maxillary, mandibular)
• Clinical test = Jaw tone; muscle bulk; sensation to face, cornea, and nasal mucosa
• Signs of dysfunction = Masticatory muscle atrophy; dropped jaw if bilateral; hypalgesia or analgesia of the face and/or cornea

Question 6

CN 6

• Name
• Function
• Clinical test
• Signs of dysfunction

Answer 6

• Name = Abducens
• Function = Motor to lateral rectus and retractor bulbi muscles
• Clinical test = Physiologic nystagmus; resting eyeball position
• Signs of dysfunction = Medial strabismus

Question 7

CN 7

• Name
• Function
• Clinical test
• Signs of dysfunction

Answer 7

• Name = Facialis
• Function = Motor to muscles of facial expression; parasympathetic to lacrimal glands; sensory (taste) to rostral tongue
• Clinical test = Menace response; palpebral reflex; lip retraction; ear movement and position in animals with erect ears; Schirmer tear test
• Signs of dysfunction = Inability to close eyelid, move ear, or retract lip; deviation of nasal philtrum (contralateral); dry eye; alternatively hemifacial tetany where the nasal philtrum is deviated toward the affected side

Question 8

CN 8

• Name
• Function
• Clinical test
• Signs of dysfunction

Answer 8

• Name = Vestibulocochlearis
• Function = Balance; hearing
• Clinical test = Body and head posture; gait; eye movement and position; hearing
• Signs of dysfunction = Head tilt; vestibular ataxia; nystagmus; positional strabismus; deafness

Question 9

CN 9

• Name
• Function
• Clinical test
• Signs of dysfunction

Answer 9

• Name = Glossopharyngeus
• Function = Sensory and motor to pharynx
• Clinical test = Gag reflex; ability to swallow
• Signs of dysfunction = Diminished gag reflex; dysphagia

Question 10

CN 10

• Name
• Function
• Clinical test
• Signs of dysfunction

Answer 10

• Name = Vagus
• Function = Sensory and motor to pharynx, larynx, and viscera
• Clinical test = Gag reflex; oculocardiac reflex; observation of inspiratory stridor
• Signs of dysfunction = Diminished gag reflex; dysphagia; laryngeal paralysis; megaesophagus

Question 11

CN 11

• Name
• Function
• Clinical test
• Signs of dysfunction

Answer 11

• Name = Accesorius
• Function = External branch (motor to trapezius); internal branch (joins CN X to innervate the larynx)
• Clinical test = Evaluation of muscle mass of the dorsal aspect of the shoulder; observation of inspiratory stridor
• Signs of dysfunction = Atrophy of trapezius muscle; laryngeal paralysis

Question 12

CN 12

• Name
• Function
• Clinical test
• Signs of dysfunction

Answer 12

• Name = Hypoglossus
• Function = Motor to tongue muscles
• Clinical test = Evaluation of tongue
• Signs of dysfunction = Atrophy of tongue; inability to retract tongue if bilateral