Cranial Nerves 2

Question 1

What is the path of CN via

Answer 1

Lower pons (junction between pons and medulla)
Enters petrous part of temporal bone via internal acoustic meats
Three branches within petrous bone
- greater petrosal nerve
- chords tympani nerve
- nerve to stopedius
Exits through base of skull (stylomastoid foramen)
Then gives extracranial branches which supplies the muscles of facial expression - temporal, zygomatic, buccaneers, marginal mandibular, cervical

Question 2

Describe teh function of cn vii

Answer 2

Special sensory - Anterior 2/3 of tongue (taste) - special sensory

Autonomic - Lacrimal glands (tears), mucosal glands in nose and roof of mouth, salivary glands (all except parotid gland)

Motor: muscles of facial expression

General sensory - Small area of the external ear

Question 3

What determines the fibres that will form a cranial nerve

Answer 3

See slide

Question 4

What are the 2 roots of the facial nerve

Answer 4

Facial nerve described as having two roots at cerebellopontine angle
• Motor root (larger- just motor axons )
• Nervus intermedius (sensory & parasympathetic
axons)

Question 5

Describe the paths of the branches of the facial nerve

Answer 5

See slide

Question 6

What are clinical points about cn vii

Answer 6

• Clinical testing is mainly by testing muscles of facial expression and the corneal reflex
• Given its many functions, facial nerve lesions can present with a variety of signs and symptoms depending on where along the nerve route the pathology is
• Important therefore to ask about other symptoms e.g. hyperacusis (sensitivity to Loud noises - problem with nerve to stapedius), dry eyes, altered taste
• Middle ear pathology (in petrous bone) can sometimes involve the facial nerve
• Close relationship with vestibulocochlear nerve within posterior cranial fossa and both
enter internal acoustic meatus
• Extracranial branches of facial nerve have close relationship with parotid gland
Benign condisiotns of parotid gland such as mumps do not usually involve facial nerve. Malignancies eg parotid cancer

Question 7

What are the afferent and efferent limbs of the corneal reflex

Answer 7

Va - afferent

Facial efferent

Question 8

Descrbe the path of cn viii

Answer 8

Cochlea + Semicircular canals (vestibular system)
->
Vestibulocochlear nerve ->
Internal acoustic meatus ->
Lower pons (junction between pons and medulla)

Question 9

What is the function of cn viii

Answer 9

Special Sensory

Hearing and balance

Question 10

What are clinical pointsa bout cn viii

Answer 10

• Clinical testing will involve testing hearing and enquiring about balance
• Damage involving cochlea, cochlear component of vestibulocochlear nerve, or brainstem nucleus causes hearing loss (sensorineural)
• Presbyacusis: a type of old-age related hearing loss
• Pathology involving semicircular canals, vestibular component of vestibulocochlear nerve, or brain nucleus causes disturbance of balance (vertigo)
• Acoustic neuroma: benign tumour involving vestibulocochlear nerve

Question 11

What are is an acoustic neuroma

Answer 11

Acoustic Neuromas are benign tumours of the Schwann cells surrounding (the vestibular component of) CN VIII. Their physical presence causes compression of the whole nerve +/- CNs in close proximity

Symptoms and Signs include 
• Unilateral hearing loss 
• Tinnitus 
• Vertigo 
• Numbness, pain or weakness down one half of face

Question 12

Describe the path of cn IX X XI XII

Answer 12

IX X and XI All exit via jugular foramen with IJV
XII - exits via hypoclossal canal
All 4 cranial nerves arising from the medulla exit base of skull to enter into superior part of carotid sheath: most quickly exit to travel towards target tissues Only cranial nerve X runs length of carotid sheath

Question 13

What are the functions of cn IX

Answer 13

General sensation (main function)
• (Palatine) tonsils and oropharynx
• Middle ear and tympanic membrane (inner surface)
• Sensory from carotid body and sinus

Special sensory
• Taste and general sensation pos. 1/3 tongue

Autonomic
• Carries parasympathetic innervation to parotid gland

Motor
• Supplies one muscle (stylopharyngeus) which assists in swallowing

Question 14

What are clinical points about cn IX

Answer 14

• Gag reflex (sensory limb): only tested if concerns around swallowing and integrity of nerves
involved in this reflex
• Taste not formally tested
• Tested in conjunction with vagus nerve (CN X) - Baker the neck contracting in
• Isolated lesions of CN IX are rare

Question 15

What os the path of cn x

Answer 15

Medulla
Juglar foramen
Carotid sheath
Through neck, into thorax and abdomen
Gives many branches on its route down the length f the neck - innervated many structures

Question 16

What is the function of cn x

Answer 16

General Sensory
• Sensory to lower pharynx, and larynx
• (Sensory to posterior part of external ear and tympanic membrane)

Motor
• Muscles of soft palate, pharynx, larynx

Autonomic
• Parasympathetic to thoracic (e.g. heart, tracheobronchial tree) and
abdominal viscera

Question 17

What are sime branches of cn x

Answer 17

Right vagus nerve runs in carotid sheath
Right recurrent laryngeal nerve turns under right subclavian
Left vagus nerve runs in carotid sheath
Left recurrent laryngeal nerve turns under arch of aorta

Question 18

What are clinical points about cn x

Answer 18

• Note patient’s speech, cough and ability to swallow
• Note movement of uvula and soft palate when saying ‘Aaah’ - normal movement - both sides of soft palate move up
• Gag reflex (efferent limb)
• Isolated lesions of CN X are rare
• Injury to its branches e.g recurrent laryngeal nerve following thyroid surgery can cause hoarseness
and dysphonia

Question 19

What is teh function of cn XI

Answer 19

Motor to sternocleidomastoid and trapezius

Question 20

What is teh route of cn XI

Answer 20

Emerges through jugular foramen
Passes deep to SCM and provides its motor innervation
Runs posterolaterally across posterior triangle
Enters deep to trapezius and provides its motor innervation

Question 21

What are clinical points about cn XI

Answer 21

Shrug shoulders against
resistance (trapezius)
• Turn head against resistance
(sternocleidomastoid
• Spinal accessory runs inferiorly through neck in posterior triangle (is quite superficial)
• Susceptible to injury in this area e.g. in lymph node biopsies, surgery, stab wound

Question 22

What is the function of cn xii

Answer 22

Muscles of the tongue (all except one)

Question 23

What is the route of cn xii

Answer 23

CN XII runs medial to angle of mandible; Crosses internal and external carotid arteries in neck
Wont see it uncles mandible removed

Question 24

What are clinical points about cn xii

Answer 24

• Inspection and movement of
the tongue
• Rare • Damage to CN XII causes weakness and atrophy of
the tongue muscles on ipsilateral side