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AHNNA > L16: Cranial nerves continued > Flashcards

L16: Cranial nerves continued Flashcards

1
Q

What can cause cranial nerve dysfunction?

A

Arise due to injury/lesion involving:
-cranial nerve during its route outside the CNS
-brainstem (where CN nuclei are located)
In the brainstem there would be other signs and symptoms

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2
Q

What is the route of the trigeminal nerve?

A
  • comes off the pons
  • it then gives rise to a trigeminal ganlion which then splits into 3 divisions (opthalmic/maxillary/mandibular)
  • opthalmic/maxillary travel through cavernous sinus
  • each division passes through different holes in the skull to reach their target
  • there are distal branches of each (dermatomes)
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3
Q

What is the main function of the trigeminal nerve?

A

Main sensory nerve supplying facial structures

-it also carries motor fibres to the muscles of mastication

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4
Q

What are the important distal branches of the trigeminal nerve?

A

Va: opthalmic

  • frontal nerve (run out of front of orbit and extend to scalp: supratrochlear and supraorbital)
  • nasociliary nerve (zoster lies dormant in trigeminal ganglia, and usually affects Va, rash only extends down to tip of nose if there is involvment of the nasociliary branch)

Vb: maxillary

  • infra-orbital nerve (runs beneath the orbit, emerges through the infraorbital foramen to innervate skin. Running beneath the orbit makes this nerve susceptible to injury. Innervates sesnory function on patch of skin on the cheek)
  • superior alveolar nerve (innervate sensory info from teeth and gums, these run up and join the infraorbital nerve. These nerves may also be damaged due to infraorbital fracture.)

Vc: mandibular (carries motor as well as sensory and runs through the infratemporal fossa)

  • auriculotemporal nerve (sensory info form lateral aspect of scalp and ear)
  • lingual nerve (general sensory info from anterior 2/3 of tongue)
  • inferior alveolar nerve (sensory info from lower jaw. Runs through bone of the mandible, it emerges from the mental foramen where it is now called the mental nerve which carries sensory info from tip of chin and teeth/gums)
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5
Q

What is Hutchinson’s sign?

A

Presence of rash on tip of nose from zoster virus

  • increases chance of front of eye being affected by shingles
  • sight threatening
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6
Q

Which nerve is vulnerable in mandibular fractures?

A

Inferior alveolar nerve/mental nerve
-as it runs through the mandible
Dentists inject local anaesthetic near the mandibular foramen, where the inferior alveolar nerve emerges from. This means numbness of teeth and gums but due to close proximity of lingual nerve you often numb the tongue.

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7
Q

What is the function of the facial nerve?

A

-motor
-special sensory
-parasympathetic
Arises from the junction between the pons and medulla (pontomedullary junction)

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8
Q

What are the target tissues of the facial nerve?

A
  • motor function: muscles of facial expression and muscle in ear
  • sensory function: taste from anterior 2/3 of tongue
  • parasympathetic function to glands (tears, salivary but not parotid, mucosal)
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9
Q

How do you examine the facial nerve?

A

Examine muscles of facial expression (motor elements)

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10
Q

What do you see with a lesion to the facial nerve?

A

Unilateral facial droop and other symptoms due to absence of other facial nerve functions

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11
Q

What can cause a facial nerve lesion?

A
  • lesions in/around internal acoustic meatus and posterior cranial fossa tumour
  • basal skull fracture involving petrous bone
  • middle ear disease
  • inflammation of facial canal e.g. facial nerve palsy/Bell’s palsy/Ramsay-Hunt syndrome
  • parotid disease as the facial nerve runs through this gland
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12
Q

How do you differentiate between Bell’s palsy and Ramsay-Hunt syndrome?

A

Ramsay-hunt presents with vesicles/rash around the ear

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13
Q

What is the route of the facial nerve?

A
  • emerges from the pons, and traverse the posterior cranial fossa
  • pass through internal acoustic meatus which passes it into the petrous bone
  • inside the petrous bone it gives off three branches, and the rest of the facial nerve continue inside the petrous bone in the facial canal
  • the facial canal has a close relationship with the middle ear
  • emerges through base of skull through the stylomastoid foramen
  • it has an important relationship with the parotid gland
  • gives off several extracranial branches to muscles of facial expression
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14
Q

If you damage the facial nerve before it enters the petrous bone, what do you damage?

A

All parts of the facial bone

  • parasympathetic, motor and sensory functions
    e. g. posterior cranial fossa tumours
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15
Q

What is the detailed course of the facial nerve within the petrous bone?

A
  • enters the petrous bone via the internal auditory meatus
  • it reaches the geniculate ganglion (where cell bodies of the sensory nerves collect), indicates the point where the 3 branches come off
  • Greater petrosal nerve: one branch consisiting of just parasympathetic fibres to lacrimal glands, nasal, oral/mucosal glands. This emerges out of the petrous bone and passes through the pterygopalatine fossa
  • the rest of the facial nerve runs through the facial canal in the middle ear, where it gives off a motor branchand another branch
  • the second branch is the nerve to stapedius (tiny muscle in middle ear)
  • the third branch called the chorda tympani which carries special sensory from anterior 2/3 of tongue, some parasympathetic nerves go down to oral cavity
  • this leaves therest of the facial nerve which comes out of base of skull through the stylomastoid foramen and it completely motor, going through the parotid gland and gives off 5 branches
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16
Q

How do we tell the difference between a facial nerve lesion and a stroke?

A

Forehead is spared in a stroke
Nerve lesion: affecting facial nerve as it exits the pons so a lesion will affect all motor elements to that half of the face
Stroke (blocked blood vessel on one side of brain): involves pathway from primary motor cortex to facial nerve, but the cranial nerves have dual cortical innervation. There is an ipsilateral route, but in the facial nerve this only backs up the motor fibres affecting the upper part of the face. (whereas the muscles of the lower part of the face do not have an ipsilateral backup)

17
Q

What is the function of the vestibulocochlear nerve?

A

Complete special sensory nerve

  • sense of hearing and balance
  • arise from pontomedullary junction
18
Q

What is the course of the vestibulocochlear nerve?

A
  • leaves pons at pontomedullary junction but a bit more caudal than the trigeminal nerve
  • enters the petrous bone from the pons via the internal acoustic meatus
  • the nerve then splits and goes to the vestibular system (balance) and the cochlea (hearing)
19
Q

How do you test for the vestibulocochlear nerve?

A

Gross bedside hearing tests (whisper/finger rub) and tuning fork testing
-ask if there is any change in hearing or balance

20
Q

How do patients present with lesionto vestibulocochlear nerve?

A
  • hearing loss
  • dizziness (vertigo)
  • tinnitus
21
Q

What causes some vestibulocochlear nerve lesions?

A
  • Vestibular schwannoma (effects the schwaan cells around the nerve) and other posterior cranial fossa tumours
  • occlusion of its blood supply (labyrinthine artery)
  • base of skull fractures involving petrous bone
  • brainstem lesion
22
Q

What are the signs and symptoms of someone with a a vestibular schwannoma?

A

-unilateral hearing loss
-tinnitus
-vertigo
-numbness/pain/weakness down one side of the face, due to pressure on the trigeminal nerve
(may also start to squash the facial nerve)

23
Q

What 2 nerves rise from the medulla that tend to be examined together?

A
  • glossopharyngeal and vagus
  • run through posterior cranial fossa and exit through the jugular foramen
  • enter into the carotid sheath
  • most of the glossopharyngeal nerve exits the carotid sheath with the external carotid
24
Q

What are the target tissues of the vagus and glossopharyngeal nerve?

A

Glossopharyngeal
(mainly sensory, does have motor elements)
-sensation of the oropharynx and tonsils (palatine in particular)
-special sense from posterior 1/3 of tongue
-contibutes to 1 swallowing muscle
-parasympathetic to parotid gland
-gives a branch called the carotid sinus branch which gives signals from carotid sinus/body

Vagus 
(motor and sensory)
-muscles of larynx and pharynx, and soft palate
-sensory from larynx and laryngopharynx
-parasympathetic to many tissues
25
Q

What are the signs and symptoms associated with lesions to vagus/glossopharyngeal nerves?

A
  • difficulty swallowing
  • weak cough
  • difficulties with speech or changes in voice
26
Q

How do you test the vagus/glossopharyngeal function??

A

Ask them to speak, swallow, cough
-look at soft palate movement
(each half ofthe soft palate is innervated by the vagus nerve, uvula stays in centre normally, if you have lesion on one side, the uvula deviates from the weaker side)
-gag reflex (touching oropharynx: glossopharyngeal sensory relay to medulla, output is for pharyngeal muscles to constrict)

27
Q

What are some lesion causes to the vagus/glossopharyngeal nerve?

A
  • Disease/pathology of the recurrent laryngeal nerve (branch of vagus nerve)
  • pathology involving carotid sheath structures
  • posterior cranial fossa tumours
  • brainstem lesions
28
Q

What is the relationship between the vagus/glossopharyngeal nerves and blood vessels?

A
  • glossopharyngeal exits the carotid sheath and passes behind the external carotid artery
  • vagus nerve follows the legnth of the carotid sheath
29
Q

What are some of the key branches of the vagus nerve?

A

Recurrent laryngeal nerve
-on the right it loops under the right subclavian
-on the left it loops under the arch of the aorta
Runs in groove b/w trachea and oesophagus and they move up to the muscles of the larynx

30
Q

Where do the accessory and hypoglossal nerves arise from?

A

Medulla
-accessory nerve does also take routes from the upper cervical spinal nerves
They both run through the posterior cranial fossa
-accessory nerve runs through jugular foramen, hypoglossal nerve runs through the hypoglossal canal
Enter the carotid sheath- but have a short journey in here before exiting
-hypoglossal nerve exits and travels towards the tongue
-accessory nerve exits and heads towards the posterior triangle

31
Q

What is the function of the hypoglossal nerve?

A

Purely motor

-responsible for tongue movements and protrusion

32
Q

What can cause hypoglossal nerve lesions?

A

-Surgery/pathology to or involving the upper carotid sheath, internal and external carotid artery
(because at level of the mandible, it superficially crosses the internal and external carotid arteries)
-posterior cranial fossa tumours

33
Q

How do you pick up hypoglossal nerve damage on examination?

A

Both sides of the tongue are equal strength so the tip of the tongue should stay inthe midline

  • damage to hypoglossal nerve, muscle in tongue on affected side becomes weak
  • protude tongue by genioglossus muscle, unaffected side will be unopposed by muscle of opposite side, so tongue deviates towards the weaker half
34
Q

What are the key target tissues of the accessory nerve?

A

Purely motor
-SCM
-trapezius
Test actions of these: turning head, and shrugging shoulders against resistance

35
Q

How would you cause a lesion to the accessory nerve?

A
  • injuries/surgery/pathology involving the posterior triangle
  • posterior cranial fossa tumours
  • base of skull fractures
  • brainstem lesions
36
Q

What is the route of the accessory nerve once out of the jugular foramen?

A
  • passes behind the SCM and innervates it
  • then runs through the posterior triangle (where it is vulnerable)
  • enters the trapezius muscle
37
Q

How can you see clinically an accessory nerve lesion?

A

Wasting of the trapezius muscle

  • difficulty in certain shoulder movements (involving movement of the scapula e.g. abducting beyond 90 degrees)
  • shoulder droop

AHNNA (25 decks)

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