Lecture 9- CN VI- VIII

Question 1

CN VI

Answer 1

abducens

Question 2

where does abducens (VI) arise from

Answer 2

bottom of the pons

Question 3

abducens is purely

Answer 3

motor

Question 4

which one muscle does abducens supply

Answer 4

• Supplies one muscle the moves the eye- lateral recuts
  
  • Helps move eye away from the midline (abduction- abducens)

Question 5

• Testing the Abducens

Answer 5

• Inspection of resting gaze
• Eye movements- e.g. ask to abduct

Question 6

• If lesions in abducens

Answer 6

• Report double vision (dipoplia- worse in lateral gaze on side of lesion)
• Abnormal eye position
• Difficulty/ unable to move affected eye laterally

Question 7

• Causes of lesions on abducens

Answer 7

• Microvascular ischaemia (diabetes/ hypertension >50)
• Head injury
• Tumour
• Raise ICP –>most commonly involved cranial nerve that arises as- A result of raised intracranial pressure- false localising sign

Question 8

Route of the abducens (CN VI)

Answer 8

1. Arises from lower part of the pons (nearer the pons medullary junction)
   
   1. Means its got a steep upwards route before it can travel through the cavernous sinus
   2. More vulnerable to raised ICP- due to herniation of other parts of the brain- causes stretching of the abducens nerve
2. Passes into the orbit via the superior orbital fissure

Question 9

Cranial Nerves that supply the eye and cause eye movement

Answer 9

• Oculomotor III
• Trochlear IV
• Abducens VI (most vulnerable because it runs in the middle of the CS)
  
  • All exit brain diff levels
  • Pass through cavernous sinus (lateral wall)
  • Enter orbit via the superior orbital fissure

Question 10

CN VII

Answer 10

facial nerve

Question 11

Facial nerve carries what sort of fibres

Answer 11

• Motor, special sensory (taste), parasympathetic

Question 12

where does facial nerve (VII) arise from

Answer 12

the junction between the pons and medulla

Question 13

• Target tissues of VII

Answer 13

• Muscles of facial expression
• Little muscle in middle ear
• Taste from anterior 2/3 of tongue
• Glands
  
  • Lacrimal
  • Salivary

Question 14

• Examination of facial nerve

Answer 14

• • Muscles of facial expression

Question 15

• Facial nerve lesion

Answer 15

• E.g.
  
  • Lesions in/around acoustic meatus and posterior cranial fossa tumours
  • Basal skull fracture (including petrous bone)
  • Middle ear disease
  • Inflammation in facial canal… facial nerve palsy e.g. bells Palsy’s, Ramsay Hunt syndrome (has to have vesicles)
  • Parotoid disease
• Sign- Unilateral facial droop (whole half of affected side )

Question 16

Route of the facial nerve

Answer 16

1. Facial nerve emerges from the pontomedullary junction (from the pons)
2. Passes through the internal acoustic meatus which brings us into the petrous bone
3. Gives off three branches
4. The rest of the facial nerve continues
   
   1. Close relationship with middle ear as it runs through bony channel- facial canal
5. Emerges through the base of the skull via the stylomastoid foramen
6. Relationship with parotid gland
7. Gives several extracranial branches= muscles of facial expression

Question 17

Facial nerve and the petrous part of the temporal bone

Answer 17

• Enters into the petrous bone via the internal auditory meatus
• Then enters into a structure called the geniculate ganglion (sensory ganglion)- geographical marker – where the first of the intrapetrous branches arise
  
  1. Greater petrosal nerve
     
     • Comes out of the petrous bone eventually arises at glands within the eye, nose and oral cavity
     • Via the pterygopalatine fossa
     • Purely parasympathetic – lacrimal, mucosal and salivary gland
  2. Nerve to stapedius
     
     • Motor branch to tiny muscle (stapedius) in the middle ear
  3. Chorda tympani
     
     • Sensory and parasympathetic
     • Special sensory taste
• Rest of the facial nerve comes through the petrous temporal bone via the stylomastoid foramen and gives off the rest of the branches of the facial nerve
  
  1. Temporal
  2. Zygomatic
  3. Buccal
  4. Marginal mandibular branch
  5. Cervical

Question 18

lesion on nerve to stapedius

Answer 18

The nerve to stapedius arises from the facial nerve to supply the stapedius muscle. The branch is given off in the facial nerve’s mastoid segment, as it passes posterior to the pyramidal process. Damage to this branch with resulting paralysis of stapedius leads to hypersensitivity to loud noises (hyperacusis).

Question 19

how to tell if its bells palsy or a stroke

Answer 19

difference is if the forehead is spare (can they furrow?)

Question 20

if bells palsy

Answer 20

forehead not spared

Question 21

if a stroke

Answer 21

the forehead is spared

Question 22

why is the forehead spared in stroke

Answer 22

Dual cortical input (due to loss of contralateral input)- ipsilateral input for muscle fibres of the upper part (not lower) of the face can be savedà therefore if stroke can furrow both eyebrows.

Question 23

CN VIII

Answer 23

vestibulocochlear

Question 24

CN VIII- Vestibulocochlear is purely

Answer 24

special sensory

Question 25

where does CN VIII- Vestibulocochlear arise from

Answer 25

pons (pontomedullary junction)

Question 26

route of the CN VIII- Vestibulocochlear

Answer 26

1. Arises from the pons (pontomedullary junction)
2. before entering petrous bone via the internal acoustic meatus
3. and then it branches to the vestibular system (balance) and the cochlea (hearing)

Question 28

• Examination of vestibulocochlear

Answer 28

Gross bedside hearing tests (whisper/ finger rub) and tuning fork testing

Question 29

• Vestibulocochlear lesions symptoms and signs

Answer 29

• Hearing loss- unilateral
• Dizziness (vertigo)
• Tinnitus
• numbness, pain, weakness down one half of face 9close relationship top facial nerve

Question 30

• Causes of lesions of CN VIII

Answer 30

• Vestibular schwannoma (and other posterior cranial fossa tumours)
  
  • Primary cancer affecting scwanna cells
  • Benign- but causes compression
  • Symptoms and sings
    
    • Unilateral hearing loss
    • Tinnitus
    • Vertigo
    • Numbness, pain or weakness down one half of face (close relationship to facial nerve)
• Occlusion of labyrinthine artery
• Base of skull fracture involving petrous bone
• Brainstem lesions (pons- vv rare)