Cranial nerves - function

Question 1

Cranial Nerves involved in Speech and Swallowing

Answer 1

Trigeminal (V), Facial (VII), Vestibulocochlear (VIII), Glossopharyngeal (IX), Vagus (X), Hypoglossal (XII)

Question 2

Cranial Nerves involved in Respiration

Answer 2

Spinal Accessory (XI)

Question 3

Cranial Nerves involved in Reading

Answer 3

Optic (II), Occulomotor (III), Trochlear (IV), Abducens (VI)

Question 4

Optic Nerve (CN II) Functions

Answer 4

• Carries neural signals from the retina to the brain

- The medial (nasal) half of the retina receives information from the lateral half of the visual field

Question 5

Symptoms of Optic Nerve (CNII) Dysfunction

Answer 5

Common
- Reduced visual acuity = blurred vision
- Visual field defects = reduced or absent vision in part of visual field in one or  both eyes
Less common
- Desaturated colour vision

Question 6

Occulomotor Nerve (CN III) Function

Answer 6

• Innervates most of the extraocular muscles (muscles
  that move the eyeball)
• Innervates the muscle that lifts the upper eyelid
  (levator palpebrae superioris) to keep the eye open
• Innervates some of the muscles that control pupil size
  and lens shape in the eye

Question 7

Symptoms of Occulomotor Nerve (CN III) dysfunction

Answer 7

• Double vision (diplopia, Gr. di- ‘two’ + ops ‘eye’)

- Drooping upper eyelid (ptosis = Gr. ‘to fall’)

Question 8

Trochlear (CN IV) and Abducens (CN VI) Nerve Function

Answer 8

• CN IV supplies the superior oblique muscle, which turns the eye downwards and inwards
• CN VI supplies the lateral rectus muscle, which pulls the eye sideways away from the nose (laterally)

Question 9

Symptoms of Trochlear (CN IV) and Abducens (CN VI) dysfunction

Answer 9

Diplopia (double vision)

Question 10

Trigeminal (CN V) Nerve Function (sensory and motor)

Answer 10

CN V sensory functions:

• Facial proprioception (feeling the position of facial muscles and jaw)
• Touch, pain and temperature sensation on face

CN V motor functions:
- Innervates the muscles of mastication

Question 11

Symptoms of Trigeminal (CN V) Nerve dysfunction

Answer 11

Sensory symptoms – altered or reduced sensation on the face and inside the mouth = paraesthesia (para ‘irregular’ + Gr. aesthesis ‘sensation’)

Sensory symptoms on same side as cranial nerve lesion (ipsilateral)

Motor – difficulty chewing, jaw deviates towards side of lesion when opening mouth (due to unopposed action of muscles on intact side)

Question 12

Facial Nerve (CN VII) Function - summary

Answer 12

Motor

• Muscles of facial expression
• Stapedius (middle ear)

Sensory
-Cutaneous (skin) sensation to external auditory meatus

Special sensory
-Taste to anterior 2/3 of tongue

Autonomic
-Lacrimal & salivary glands

Question 13

Symptoms of Facial Nerve (CN VII) dysfunction

Answer 13

Motor
-Ipsilateral weakness of muscles of facial expression

Sensory
-Altered cutaneous sensation around ipsilateral external auditory meatus

Special sensory

• Altered taste on ipsilateral anterior 2/3 of tongue
• Sounds are loud in ipsilateral ear (if nerve to stapedius affected)

Autonomic
-Dry mouth and eyes, due to reduced parasympathetic supply to lacrimal & salivary glands

Question 14

Function of Vestibulocochlear/Acoustic Nerve (CN VIII) and symptoms of dysfunction

Answer 14

Function
-Sensory nerve from the cochlear to the brainstem

Dysfunction

• Hearing loss
• Tinnitus (continuous ringing noise)
• Altered balance

Question 15

Glossopharyngeal Nerve (CN IX) function

Answer 15

Sensory

• Pharynx, posterior 1/3 of tongue
• Cutaneous sensation external ear
• Gag reflex - afferent = CN IX (+ CN X); efferent = CN X

Motor
-Stylopharyngeus – elevates larynx and
pharynx, dilates pharynx during swallowing

Special sensory
-Taste to posterior 1/3 tongue

Autonomic
-Parotid salivary gland

Question 16

Symptoms of Glossopharyngeal Nerve (CN IX) dysfunction

Answer 16

• Symptoms may be subtle or absent
• Altered bitter/sour taste
• Reduced pharyngeal sensation
• Mild dysphagia

Question 17

Symptoms of Vagus Nerve (CN X) dysfunction

Answer 17

Altered voice

• Vocal fold paralysis due to recurrent laryngeal nerve or vagus nerve lesions
• Unilateral lesions - hoarse, weak or breathy voice, vocal fatigue
• Bilateral complete lesions – aphonia
• Superior laryngeal nerve lesion – vocal folds can still adduct for phonation, but cricothyroid muscle weakness causes loss of pitch control, especially in upper pitch range

Noisy breathing (stridor), ineffective cough, shortness of breath

Dysphagia, aspiration, choking or coughing when swallowing

(Other symptoms relating to autonomic functions of CN X, e.g. gastroparesis – reduced contraction of intestinal muscles leading to nausea or stomach pain)

Question 18

Vagus Nerve (CN X) Function

Answer 18

The pharyngeal branch of the vagus nerve innervates the muscles of the soft palate and the pharynx (except Stylopharyngeus), and intrinsic muscles of the larynx

Question 19

Spinal Accessory Nerve (CN XI) Function and symptoms of dysfunction

Answer 19

Functions

• Spinal accessory nerve supplies motor innervation to:
  
  • Trapezius muscle - elevates shoulder (e.g. shrug)
  • Sternocleidomastoid muscle – turns head to contralateral side

Symptoms of dysfunction

• Shoulder weakness, head tilt
• Breathless on exertion (weakness of accessory muscles of respiration)

Question 20

Hypoglossal Nerve (CN XII) Function

Answer 20

Functions

• Hypoglossal nerve provides motor innervation for:
  
  • All extrinsic tongue muscles except palatoglossus (CN X)
  • All intrinsic tongue muscles

Symptoms of dysfunction

• Tongue weakness
• Dysarthria
• Difficulty moving food around mouth when chewing