Lecture 9- CN VI- VIII Flashcards
CN VI
abducens
where does abducens (VI) arise from
bottom of the pons
abducens is purely
motor
which one muscle does abducens supply
- Supplies one muscle the moves the eye- lateral recuts
- Helps move eye away from the midline (abduction- abducens)
- Testing the Abducens
- Inspection of resting gaze
- Eye movements- e.g. ask to abduct
- If lesions in abducens
- Report double vision (dipoplia- worse in lateral gaze on side of lesion)
- Abnormal eye position
- Difficulty/ unable to move affected eye laterally
- Causes of lesions on abducens
- 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
Route of the abducens (CN VI)
- Arises from lower part of the pons (nearer the pons medullary junction)
- Means its got a steep upwards route before it can travel through the cavernous sinus
- More vulnerable to raised ICP- due to herniation of other parts of the brain- causes stretching of the abducens nerve
- Passes into the orbit via the superior orbital fissure
Cranial Nerves that supply the eye and cause eye movement
- 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
CN VII
facial nerve
Facial nerve carries what sort of fibres
- Motor, special sensory (taste), parasympathetic
where does facial nerve (VII) arise from
the junction between the pons and medulla
- Target tissues of VII
- Muscles of facial expression
- Little muscle in middle ear
- Taste from anterior 2/3 of tongue
- Glands
- Lacrimal
- Salivary
- Examination of facial nerve
- Muscles of facial expression
- Facial nerve lesion
- 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 )
Route of the facial nerve
- Facial nerve emerges from the pontomedullary junction (from the pons)
- Passes through the internal acoustic meatus which brings us into the petrous bone
- Gives off three branches
- The rest of the facial nerve continues
- Close relationship with middle ear as it runs through bony channel- facial canal
- Emerges through the base of the skull via the stylomastoid foramen
- Relationship with parotid gland
- Gives several extracranial branches= muscles of facial expression
Facial nerve and the petrous part of the temporal bone
- 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
- 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
- Nerve to stapedius
- Motor branch to tiny muscle (stapedius) in the middle ear
- Chorda tympani
- Sensory and parasympathetic
- Special sensory taste
- Greater petrosal nerve
- 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
- Temporal
- Zygomatic
- Buccal
- Marginal mandibular branch
- Cervical
lesion on nerve to stapedius
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).
how to tell if its bells palsy or a stroke
difference is if the forehead is spare (can they furrow?)
if bells palsy
forehead not spared
if a stroke
the forehead is spared
why is the forehead spared in stroke
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.
CN VIII
vestibulocochlear
CN VIII- Vestibulocochlear is purely
special sensory
where does CN VIII- Vestibulocochlear arise from
pons (pontomedullary junction)
route of the CN VIII- Vestibulocochlear
- Arises from the pons (pontomedullary junction)
- before entering petrous bone via the internal acoustic meatus
- and then it branches to the vestibular system (balance) and the cochlea (hearing)
- Examination of vestibulocochlear
Gross bedside hearing tests (whisper/ finger rub) and tuning fork testing
- Vestibulocochlear lesions symptoms and signs
- Hearing loss- unilateral
- Dizziness (vertigo)
- Tinnitus
- numbness, pain, weakness down one half of face 9close relationship top facial nerve
- Causes of lesions of CN VIII
- 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)
