8. Cranial Nerves Continued Flashcards
What is CNVII and where does it originate from?
Facial nerve, lateral lower pons (pontomedullary junction)
What is the path of CNVII?
Lower pons → Enters petrous bone via Internal auditory Meatus → 3 branches within petrous bone → Exits via sylomastoid foramen
What type of fibres are in CNVII?
Special sensory, Motor, parasympathetic
What autonomic fibres are in CNVII and what do they innervate?
Parasympathetic: Lacrimal glands, nasal glands, Salivary glands (except parotid)
What is the special sensory function of CNVII?
Anterior 2/3 of tongue (taste)
What is the motor function of CNVII?
Muscles of facial expression, Stapedius (in middle ear)
Where does the facial nerve first branch and what is the name of the branch?
At the geniculate ganglion in the petrous bone
- first of the three intrapetrous branches = greater petrosal nerve
What is the route of the greater petrosal nerve and where does it branch?
Leaves petrous bone and branches at pterygopalatine fossa to lacrimal, nasal and oral/palatal mucosal glands
What is the 2nd branch of the facial nerve?
nerve to stapedius - branches in middle ear cavity
What type of fibres are in the greater petrosal nerve?
purely parasympathetic
what type of fibres are in nerve to stapedius?
purely motor
If a lesion affects the nerve to stapedius how may it present?
hyperacoustic
what is the third branch of the facial nerve in the petrous bone
chorda tympani
What fibres are in the chorda tympani nerve and what are their functions?
Parasympathetic: Salivary glands
Special sensory: Anterior 2/3rd tongue
describe the route of the facial nerve after it passes through the stylomastoid foramen?
now only contain motor fibres
- route through parotid gland and gives of five terminal extra cranial branches
what are the 5 extra cranial branches of facial nerve?
To Zanzibar By Motor Car
temporal zygomatic buccal marginal mandibular cervical
How is CNVII tested?
Mainly by testing muscles of facial expression (and the corneal reflex orbicularis oculi to close the eye)
Why can symptoms of CNVII lesion vary?
Depends on where along the nerve route the pathology is
how do facial nerve lesions present?
Unilateral facial droop +/- reporting symptoms due to absence of other facial nerve functions:
Hyperacusis (noise sensitivity), dry eyes, altered taste, dry mouth
Why can middle ear and parotid pathology affect CNVII?
Occurs in petrous bone which facial nerve passes through. Passes through parotid gland.
what are some causes of facial nerve lesions?
- Lesions in/around internal acoustic meatus & posterior cranial fossa tumours - point of vulnerability
- Basal skull fracture (involving petrous bone)
- Middle ear disease
- Inflammation in facial canal…facial nerve palsy e.g. Bell’s Palsy, Ramsay-Hunt Syndrome
- Parotid disease
What is Bell’s Palsy?
facial nerve paralysis
what is Ramsay-Hunt syndrome?
Varicella zoster infecting facial nerve - shingles
what are distinguishing features of Ramsay hunt syndrome
unilateral facial droop
vesicles or rash within external ear
what is key when determining whether facial droop is due to stroke or facial nerve lesion?
forehead sparing - stroke
- Involving motor pathways anywhere along path from primary motor cortex to where synapse with facial nerve motor nuclei
Upper half of contralateral face spared (has back-up) - Involving facial nerve anywhere from from exit from brain stem And along its route to target tissue
Whole half ipsilateral face
explain how to identify if forehead spared?
if forehead affected - no furrows, cannot raise eyebrows
if forehead spared - furrows remain and able to raise eyebrows
why is the forehead spared in stroke but not facial nerve lesion?
facial nerve nuclei split into top and bottom half and top half has both contralateral and back up ipsilateral innervation from PMC so if contralateral affected in a stroke then it has a back up supply so forehead spared. lower half has only contralateral supply so leads to contralateral facial droop of lower half
if the facial nerve is affected after it has left brainstem, all motor elements it supplies will be affected on the ipsilateral side
What is CNVIII and where does it originate from?
Vestibulocochlear, from the lateral lower pons (pontomedullary junction)
What is the path of CNVIII
Cochlea & Semicircular canals (vestibular system) {within petrous bone} → Vestibulocochlear nerve → Internal Acoustic Meatus → lower pons
What type of fibres does CNVIII have?
Special sensory
What is the function of CNVIII?
Hearing and balance
How is CNVIII tested?
gross bedside hearing test (whispering 99 in each ear)* and enquiring about balance + tuning fork testing
how do CNVIII lesions present?
Hearing loss +/- dizziness (vertigo) +/- tinnitus
what are causes of CNVIII lesions?
- Vestibular schwannoma (and other posterior cranial fossa tumours)
- Occlusion of labyrinthine artery
- Base of skull fracture (involving petrous bone)
- Brainstem lesion (pons)- rare ++
What is an acoustic neuroma/Vestibular schwannoma?
Benign tumour of schwann cells surrounding the vestibulocochlear nerve, compressing the nerve
What are the signs and symptoms of acoustic neuroma?
- Unilateral hearing loss
- Tinnitus
- Vertigo
- Numbness, pain or weakness down one half of face (involvement of facial and trigeminal nerves )
Define presbyacusis.
old-age related hearing loss
Damage to what structures causes hearing loss?
Cochlea, cochlear component of vestibulocochlear nerve, or brainstem nucleus
Damage to what structures causes balance disturbance?
Semicircular canals, vestibular component of vestibulocochlear nerve, or brain nucleus
What do the 4 medullary cranial nerves enter after leaving the skull?
Carotid sheath, all exit at some point except vagus
What is CNIX and where does it originate from?
Glossopharyngeal Nerve from the lateral superior medulla
What is CNX and where does it originate from?
Vagus, from later upper medulla
describe the route of CN IX and X
Arise from medulla
Run through posterior cranial fossa
Exit through jugular foramen
Enter into carotid sheath- close relationship with internal and external carotid arteries
What type of fibres does CNIX have?
General sensory, special sensory, autonomic, motor
What is the MAIN function of CNIX?
Sensory supply of oropharynx, posterior ⅓ tongue (SS and GS)and middle ear
What is the general sensation of CNIX?
- (Palatine) tonsils and oropharynx
- Middle ear and tympanic membrane (medial side)
- Sensory from carotid body and sinus
- Pos 1/3 tongue
WHat is the special sensory of CNIX?
Taste of posterior 1/3 tongue
What is the autonomic function of CNIX?
Carries parasympathetic innervation to parotid gland
WHat is the motor function of CNIX?
Supplies one muscle (stylopharyngeus) which assists in swallowing
How is CNIX function tested?
Tested in conjunction with vagus nerve (CN X) (when asking patient to swallow)
What type of fibres are in CNX?
General sensory, motor and autonomic
What are the general sensory functions of CNX?
- Sensory to laryngopharynx, and the whole larynx
* Sensory to small part of external ear(external auditory meatus) and tympanic membrane(lateral side)
What is the motor function of CNX?
• Muscles of soft palate, pharynx, larynx
What are the autonomic functions of CNX?
Parasympathetic to thoracic (e.g. heart, tracheobronchial tree) and abdominal viscera
How is CNIX and X function tested?
tested together
Speech, swallow, cough,
soft palate movement & uvula position [CN X]
[gag reflex: IX & X]
how is soft palate elevation tested?
get patient to say AHHH
if both right and left side of soft palate innervation is intact, soft palate muscle rises equally and uvula stays in centre
if vagus nerve lesion on one side, affected side soft palate won’t elevate and uvula deviates away from weaker side
what can cause lesions of CN IX and X?
- RLN branch of CN X- (thyroid pathology or surgery; superior thorax/mediastinal pathology)
- Pathology involving carotid sheath structures (e.g. common or internal carotid artery dissection/surgery)
- Posterior cranial fossa tumours, base of skull #s (jugular foramen)
- Brainstem (medullary) lesions e.g. infarct, MND
What is CNXI and where does it originate from?
Spinal accessory nerve, Posterolateral medulla
What is CNXII and where does it originate from?
Hypoglossal nerve, lateral to medullary pyramid
describe the path of CN XI and XII
- Arise from medulla (accessory nerve also has some contribution from upper cervical spinal nerves)
- Run through posterior cranial fossa
- CNXI exit skull through jugular foramen
- CNXII exit through hypoglossal canal
- Enter into carotid sheath-
- Hypoglossal exits and travels towards tongue
- Accessory exits and heads towards posterior triangle
What type of fibres are in CNXI?
Motor
What is the function of CNXI?
Motor to sternocleidomastoid and trapezius
What is the path of CNXI?
Medulla → Jugular foramen → carotid sheath → deep to SCM → posterolaterally across posterior triangle → deep to trapezius
How is function of CNXI tested?
- Shrug shoulders against resistance (trapezius)
* Turn head against resistance (sternocleidomastoid)
Where is CNXI susceptible to damage?
- 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
causes of CNXI lesions?
fd
What is the path of CNXII?
Medulla → hypoglossal canal → carotid sheath → medial to mandible angle → between carotids
What type of fibres are in CNXII?
Motor
What is the function of CNXII?
Innervates Muscles of the tongue (all except one)
How is CNXII function tested?
Inspection and movement of the tongue, damage to CNXII cause weakness and atrophy of tongue on ipsilateral side, tongue deviates towards damaged side
describe tongue protrusion test for hypogossal damage
when asked to stick tongue out, should stay in middle. if damage to hypoglossal nerve, muscle on affected side becomes weak and so tongue deviates to weaker side.
tongue never lies
what can cause hypoglossal nerve lesions?
Inspection and movement of the tongue, damage to CNXII cause weakness and strophy of tongue on ipsilateral side, tongue deviates towards damaged side
