Lecture 9 - CN VI - XII Flashcards
4 cranial nerves that come from the pons
CN V - trigeminal
CN VI - abducens
CN VII - facial
CN VIII - vestibulocochlear
Route of the abducens nerve
- Pontomedullary junction
- Through the middle of the cavernous sinus
- Through the superior orbital fissure
- Through the orbit to the lateral rectus muscle
Role of the abducens nerve
Abduction of the eye
Suppiles motor innervation to the lateral rectus muscle
CN VI test
Test eye movements
CN VI lesion presentation
Diplopia
Cannot abduct affected eye
What causes injury to the CN VI
Microvascular complications:
- diabetes
- hypertension
Increased intracranial pressure
- tumour
- haemorrhage
CN VII role
Special sensory - taste to anterior 2/3rds of the tongue
Motor - Muscles of facial expression and nerve to stapedius
Autonomic - Parasympathetics to the :
- Submandibular and sublingual salivary glands
- Lacrimal glands
- Mucosal glands in nose
General sensory - small area of the external ear
What does the stapedius do?
Tampers the vibrations made by ossicles due to sound therefore controlling volume tolerance
Roots of the facial nerve
2 roots at the cerebellopontine angle:
- Motor root - larger
- Nervus intermedius - sensory and parasympathetic
Route of the facial nerve
- Ponto medullary junction
- The motor root and nervus intermedius converge and run through the internal acoustic meatus
- The facial nerve goes through the petrous bone, forms the geniculate ganglion and exits the petrous bone
- Splits into:
- Greater petrosal nerve
- Chorda tympani nerve
- Stapedius nerve - Exits the stylomastoid foramen
- Runs through the parotid gland to supply the muscles of facial expression
How will a lesion of the facial nerve at the internal acoustic meatus present?
All branches affected:
- Dry eyes
- Dry mouth
- Taste altered
- Increased sensitivity to loud noises - hyperacusis
- Bell’s palsy
- Loss of general sensation around ear
How will a lesion of the facial nerve at the stylomastoid foramen present?
All branches have been given off:
- Bells palsy
CN VII test
Change in taste
Test muscles of facial expression
Corneal reflex - Obicularis oculi orbital and palpebral aspect
What can cause CN VII damage?
Middle ear pathologies - close relationship to the vestibulocochlear nerve within the posterior cranial fossa as both enter the internal acoustic meatus
Tumour of the parotid gland - enlargement causes facial nerve compression
Corneal reflex
Afferent limb - Va
Efferent limb - CN VII
Route of the vestibulocochlear nerve
- The cochlear nerve and vesitibular nerve from the cochlea and the semicircular canals form the vestibulocochlear nerve
- Enter the internal acoustic meatus
- To the pontomedullary junction
CN VIII role
Balance
Hearing
CN VIII test
Hearing test
Vertigo - ask about balance
Presbyacusis
Age related hearing loss
Acoustic neuroma
and presentation
Benign tumour of the schwann cells surrounding the vestibulocochlear nerve
Growth compresses the nerve
Presentation: Unilateral hearing loss Tinnitus Vertigo Numbness, pain or weakness down one half of face
Which nerves exit the jugular foramen?
CN XI - Glossopharngeal nerve
CN X - Vagus
CN XI - Spinal accessory
Role of CN IX
Special sensory - Taste to posterior 1/3rd of tongue
General sensory - Posterior 1/3rd tongue Oropharynx Palatine tonsils Middle ear and tympanic membrane via tympanic branch Carotid body and sinus
Autonomic - Parasympathetics to the parotid gland
Motor - Supplies the stylopharyngeus
Why do patients complain of ear pain when they have a sore throat?
The glossopharyngeal nerve supplies the oropharnx and middle ear
Therefore can get referred pain from the palatine tonsils to ear even if the ear is normal
CN IX test
Tested alongside vagus nerve
Ask patient to swallow
Gag reflex
Taste - not formally tested
Gag reflex
Afferent- CN IX
Efferent - CN X and CN IX
Route of CN IX
- Medulla
- Jugular foramen
- Carotid sheath
- Exits carotid sheath early and gives off the tympanic branch which suplies the inner ear
- Continues to tongue, oropharnx and parotid gland
Route of CN X
- Medulla
- Jugular foramen
- Carotid sheath
- Through neck into the thorax and abdomen
Role of CN X
General sensory:
Lower pharynx
All of larynx
Small part of external ear and tympanic membrane
Motor -
Soft palate muscles
Pharyngeal muscles except stylopharyngeus
Laryngeal muscles
Autonomic - parasympathetic to thoracic and abdominal viscera
- heart - decrease BP
- tracheobronchial tree - bronchodilation
Branches of vagus nerve
Left and right recurrent laryngeal nerve
What do the recurrent laryngeal nerves turn under?
Left recurrent laryngeal nerve - aortic arch
Right recurrent laryngeal nerve - right subclavian artery
What muscles does the vagus nerve supply?
Laryngeal - Intrinsic muscles of the vocal cords
Cricothyroid
Pharyngeal -
Palatopharyngeus (hard palate)
Salpingopharyngeus
Superior, middle and inferior pharyngeal constrictors
Soft palate: Palatoglossus
CN X test
Changes in:
- speech - hoarseness of voice and dysphonia
- cough
- ability to swallow
- Gag reflex
- Movement of soft palate and uvula when saying ‘aah’
CN XI role
Motor innervation to:
Trapezius - shrug shoulders
SCM - lateral flexion of head and rotation
Route of CN XI
- Medulla
- Jugular foramen
- Carotid sheath and exits early
- Deep to SCM
- Passes posterolaterally across the posterior triangle
- Enters the trapezius
Lesion of the CN XI in the posterior triangle
Only the trapezius will be affected as the nerve has already supplied the SCM
CN XI test
Shrug shoulder against resistance
Turn head against resistance
How can CN XI be damaged?
Damage to the posterior triangle in e.g:
- lymph node biopsies
- surgery
- Stab wound
Role of CN XII
Motor innervation to the muscles of the tongue except the palatoglossus
What muscles does the CN XII innervate?
Genioglossus
Hypoglossus
Styloglossus
Route of CN XII
- Medulla
- Hypoglossal canal
- Runs medial to the angle of the mandible and crosses the ICA and ECA in neck
CN XII test
Weakness and atrophy of tongue on the ipsilateral side
Deviates to the side of weakness
What can damage the hypoglossal nerve?
Surgery to the jaw and upper carotid sheath
