39. Diseases of the cranial nerves in dogs and cats

Question 1

Cranial Nerves motor sensory and parasympathetic?

Answer 1

Question 2

Cranial Nerve 1?

Answer 2

CN I (OLFACTORY NERVE)

This nerve is not routinely examined; Unilateral brain lesions do not

cause anosmia (loss of sense of smell); The integration of smell is a bilateral phenomenon

Examination: Objective evaluation of smell function – Behavioural reaction (inaccurate)

Irritating substances will excite CN V sensory nerve endings and will not correlate with olfaction.

Question 3

Cranial Nerve 2?

Answer 3

CN II (OPTIC NERVE)

Examination:

§ Vision: CN II

§ PLR: CN II → CN III; Tests n. opticus integrity; doesn’t

test vision

§ Menace response (MR): CN II → CN VII; Learned

response at 10-12 weeks; Cerebellar deficit → Ipsilateral

loss of MR

§ Visual placing: CN II → Motoric innervation of the

forelimbs

Question 4

CN 3?

Answer 4

CN III (OCULOMOTOR NERVE

Pupillary sphincter muscle; Medial, dorsal, ventral recti muscles;

Ventral oblique muscle; Levator palpebrae m. superioris

Examination:

Physiological nystagmus (vestibulo-ocular reflex): Turn the head to

one side and the eye will follow the head’s position in small

fractional movements with fast phase towards the movement.

Dysfunction: Ventrolateral strabismus

Question 5

CN 4?

Answer 5

CN IV (TROCHLEAR NERVE)

Dorsal oblique muscle

Examination: Physiological nystagmus (vestibulo-ocular reflex)

Turn the head to one side and the eye will follow the head’s position

in small fractional movements with fast phase towards the

movement.

Dysfunction: Dorsolateral strabismus

Question 6

CN 6?

Answer 6

CN VI (ABDUCENT NERVE)

Lateral rectus muscle; Retractor bulbi muscle

Examination: Physiological nystagmus (vestibulo-ocular reflex)

Turn the head to one side and the eye will follow the head’s position

in small fractional movements with fast phase towards the

movement.

Dysfunction: Medial strabismus

Question 7

CN 7?

Answer 7

CN VII (FACIAL NERVE)

Motor function: Muscles of facial expression

Sensory function: Sense of taste

Autonomic function: Lacrimal glands; Mandibular glands;

Sublingual salivary glands

Examination:

§ Symmetry of the face § Blinking

§ Corneal reflex § Palpebral reflex

§ Schirmer tear test § Pinching the face

§ Menace response

The facial nerve accompanies the vestibulocochlear nerve (CN VIII)

in the internal acoustic meatus of the petrosal bone → Inflammation

& surgery of the ear can interfere with the function of CN VII

Lesion of CN VII → Facial nerve paralysis

Question 8

CN VIII?

Answer 8

CN VIII (VESTIBULOCOCHLEAR NERVE)

Function: Hearing; Vestibular function → Adaptation of eye & body

position with respect to the position & movement of the head

Vestibular system: Coordinates position of the eye, neck, trunk &

limbs with the movements of the head. Maintains equilibrium during

active & passive movement when the head is at rest

Function: Receptors detect the position & movement of the head →

Vestibular nuclei in connection with

§ The CN responsible for eye movement (CN III, IV & VI)

§ Ipsilateral extensor muscles of the limb (vestibulospinal

tract)

§ Cerebellum

Vestibular Disease

Clinical signs

§ Vestibular strabismus § Imbalance

§ Vestibular ataxia (asymmetric) § Nystagmus

§ Normal postural reactions § Head tilt

Forms

§ Peripheral (Inner ear)

§ Central (Vestibular nuclei; Cerebellum)

§ Differentiation – Other brainstem signs in central form e.g

postural reaction deficit, nystagmus changes direction with

head position

Question 9

CN 9?

Answer 9

CN IX (GLOSSOPHARYNGEAL NERVE)

Motor function: Muscles of the pharynx & palate

Sensory function: Tongue & pharyngeal mucosa – Taste

Autonomic function: Salivary glands

Examination: Swallowing & gag reflex (CN IX & X)

Dysfunction: Dysphagia (coughing after drinking)

Question 10

CN 10?

Answer 10

CN X (VAGUS NERVE)

Motor function: Pharynx; Larynx; Oesophagus

Sensory function: Pharynx; Larynx; Thoracic & abdominal viscera

Autonomic function: Thoracic & abdominal viscera (excl. pelvic

region)

Examination: Swallowing & gag reflex (CN IX & X)

Dysfunction

§ Dysphagia (coughing after drinking)

§ Laryngeal paralysis & voice changes (dysphonia)

§ Megaoesophagus (regurgitation)

Question 11

CN 11?

Answer 11

CN XI (ACCESSORY NERVE)

Internal branch → Muscles of the larynx & cranial oesophagus

External branch → Mm. trapezius, sternocephalicus et

brachiocephalicus

Dysfunction: Laryngeal paralysis; (Muscle atrophy from ext. branch lesion)

Question 12

CN 12?

Answer 12

CN XII (HYPOGLOSSAL NERVE)

Function: Motoric innervation of the tongue

Examination

§ Pasty food under the nose – can the animal lick it off?

§ Palpation → Any atrophy felt?

§ Pull the tongue → Can the animal withdraw the tongue?

Dysfunction: Unilateral atrophy of the tongue; Unilateral lingual deviation

Question 13

Pathological lesions of the cranial nerves?

Answer 13