Neurology II: Cranial Nerves & Their Disorders Flashcards
What do the cranial nerves form a part of?
The peripheral nervous system (PNS)
What are the 12 cranial nerves?
I - (Olfactory)
II - (Optic)
III - (Oculomotor)
IV - (Trochlear)
V - (Trigeminal)
VI - (Abducens)
VII - (Facial)
VIII - (Auditory or Vestibulocochlear)
IX - (Glossopharyngeal)
X - (Vagus)
XI - (Spinal Accessory)
XII - (Hypoglossal)
Describe the structure of the olfactory nerve.
-Shortest cranial nerve
-Unmyelinated
-Sensory component only
Specialised epithelium at the top of the nasal cavity contains olfactory nerve fibres
What can damage to the olfactory nerve result in and how can damage be caused?
Damage to the olfactory nerve can cause altered sense of smell, or complete loss of sense of smell (anosmia).
Causes include head injuries, tumours and neurodegenerative disorders
(Temporary changes to smell can be caused by infection)
What is the function of the olfactory nerve?
Sense of smell
How would you test to see if the patient’s olfactory nerve is functioning well?
Ask about any recent changes to sense of smell
Then, with the patient’s eyes closed, ask them to occlude one nostril and identify the smell (e.g. coffee, vanilla)
Repeat on the other sid
The optic nerve only has a sensory component, true or false?
true
What is the function of the optic nerve?
Transmission of sensory information from the retina to the primary visual cortex of the brain
What are some potential causes of optic nerve defects?
Trauma
Tumour (e.g. pituitary adenoma)
Multiple sclerosis (optic neuritis-inflammation damages optic nerve)
Stroke
What do you have to test in order to examine the optic nerve?
Visual acuity
Visual fields
Pupillary reflexes
Fundoscopy
Fundoscopy is performed with an ophthalmoscope & it allows visualisation of the retina and optic disc (optic nerve head) but this is rarely carried out in dental setting
How can visual acuity be formally assessed?
Snellen chart (letters with diff sizes) with the patient sat 6 metres away.
Colour vision is also assessed using Ishihara plates (numbers in different colours)
Dental setting: Ask the patient to read from a printed page (glasses, contact lenses should be worn)
Test one eye at a time
How can visual fields be formally assessed?
Tested through confrontation: sit facing each other with a distance of ~an arm’s length
Have the patient looking directly at your eye or nose and test each quadrant in the patient’s visual field by having them count the number of fingers that you are showing
This relies on the examiner having normal visual fields & blind spots
What are some common visual field defects?
Monocular blindness (e.g. trauma)
Bitemporal hemianopia (classically seen in acromegaly) leads to impaired peripheral vision
Homonymous hemianopia (e.g. stroke)
How is the pupillary reflex tested?
Pupillary Reflex
Darkened room
- Direct reflex – Shine the pen torch into one eye. Look for pupillary constriction of
ipsilateral eye (i.e. the eye you are shining the light into) - Consensual reflex – shine the light into the same eye as previously, but this time, observe the contralateral eye for pupillary constriction
3.Now repeat for the other eye (direct and consensual reflex)
What is being tested:
Afferent (sensory) pathway - optic nerve
Efferent (motor) pathway - oculomotor nerve
If you had a left optic nerve lesion, what would happen when testing the pupillary reflex?
Shine a pen torch into the left eye:
Left direct reflex lost (the left pupil will not constrict)
Left consensual reflex maintained (left pupil will constrict when light shone in the right eye)
Right direct pupillary response is maintained
Right consensual reflex is lost (right pupil will not constrict when light is shone into left eye)
If you had a left oculomotor nerve lesion, what would happen when testing the pupillary reflex?
Shine a pen torch into the left eye:
Left direct reflex lost
Left consensual reflex lost
Right direct reflex maintained
Right consensual reflex maintained
Which cranial nerves are usually assessed together and why?
III (oculomotor), IV(trochlear), & VI (abducens)
All 3 have a motor function and supply the extra-ocular muscles
What does the oculomotor nerve supply?
Supplies medial, superior & inferior rectus, inferior oblique, levator palpebrae superioris
Also supplies parasympathetic fibres involved in pupillary constriction
What does the trochlear nerve supply?
Superior oblique
What does the abducens nerve supply?
Lateral rectus
What will palsies of cranial nerves III, IV, & VI result in?
Diplopia - double vision
What are potential causes of palsy in the oculomotor nerve and how does it manifest?
Causes: diabetes, increased intra-cranial pressure
Manifestation: eye is fixed down and out, unless looking towards the affected side
Additional signs: ptosis (drooping), dilated pupil (mydriasis)
What is a potential cause of palsy in the trochlear nerve and how does it manifest?
Cause: trauma
Manifestation: eye cannot move down and in (vertical diplopia when looking inferiorly)
What are potential causes of palsy in the abducens nerve and how does it manifest?
Causes: stroke, multiple sclerosis
Manifestation: cannot look to the affected side
How do you test for these palsies?
Usually performed alongside cranial nerve II, after visual fields
Ask the patient to follow a pen as you draw out the letter H
Ensure they keep the head still and only move the eyes
Does the trigeminal nerve have both sensory and motor function?
yes
What are some potential causes of trigeminal nerve palsy?
Upper motor neurone lesions (i.e. within the brain cortex) include tumours, multiple sclerosis
Lower motor neurone lesions (affecting the peripheral nerve fibres) include cavernous sinus lesions, iatrogenic damage to IAN/lingual nerve
How do you test the sensory component of the trigeminal nerve?
Sensory component divided into ophthalmic (V1), maxillary (V2) and mandibular (V3) divisions
Tested through light touch and pin prick (use a Neurotip)
Corneal reflex (V1) not routinely tested
How do you test the motor component of the trigeminal nerve?
Motor component supplies muscles of mastication
Inspect temporalis/masseter for wasting
Palpate temporalis/masseter muscle bulk with patient clenching
Ask the patient to open the jaw against resistance from your hand
(Jaw jerk reflex- not routinely performed)
What functions does the facial nerve have?
Sensory for taste to the anterior 2/3rds via chorda tympani
Motor to the muscles of facial expression, nerve to stapedius
Secretomotor to lacrimal, submandibular & sublingual salivary glands
What are potential causes of facial nerve palsy?
Upper motor neurone lesions: stroke
Lower motor neurone lesions: Bell’s palsy, parotid tumour
Remember that in lower motor neurone lesions, the entire half of the face is affected
In upper motor neurone lesions, the forehead is spared (as there is bilateral innervation from the cortex)
How do you test the facial nerve?
Ask about changes to sense of taste
Ask about hearing (hyperacusis)
Facial movements (tested against resistance)- raise eyebrows, close eyelids, puff out cheeks, purse the lips, show your teeth
What is the function of the vestibulocochlear nerve?
It has a sensory function
Is involved in hearing and balance
What are some common causes of vestibulocochlear nerve defects?
Acoustic neuroma (tumour that develops on vestibular nerve)
Paget’s disease (bones grow larger+weaker)
How do you test the vestibulocochlear nerve?
Ask about changes to hearing
Whisper into the ear (choose a bi-digit number or two syllable word) and ask the patient to repeat
Rinne and Weber test are performed using a tuning fork to assess for sensorineural vs conductive deafness
What are the functions of the glossopharyngeal nerve?
Sensory and motor functions
-Principal role is sensory to tonsillar fossa and pharynx
-Taste to the posterior 1/3rd of the tongue
-Parasympathetic innervation to the parotid glands
What are some potential causes of glossopharyngeal nerve palsy?
Trauma, tumour, diphtheria
(IX nerve problems usually occur alongside CN X problems)
What will patients with a glossopharyngeal nerve palsy have?
Impaired gag reflex
(Testing gag reflex is not routinely performed)
What is the function of the vagus nerve?
Motor function supplying the pharynx, larynx and soft palate.
What are some causes of vagus nerve palsy?
Trauma, brainstem lesion
How do you test the vagus nerve (and glossopharyngeal nerve)?
Ask the patient to say ‘ah’ to visualise the uvula and soft palate.
If a deficit is present, the uvula will deviate towards the unaffected side
Gag reflex (not performed routinely)
What is the function of the accessory nerve (also known as spinal accessory nerve)?
Motor function to muscles of the neck
What is the most common cause of accessory nerve palsy?
Stroke
How do you test the accessory nerve?
Inspect for wasting of trapezius/sternocleidomastoid
Shrug shoulder against resistance (test one side at a time)
Turn the head against resistance
What is the function of the hypoglossal nerve?
Motor function to the tongue
What are some causes of hypoglossal nerve palsy?
Trauma, brainstem lesions
How do you test the hypoglossal nerve?
Ask the patient to protrude their tongue
The tongue should look symmetrical and there should not be any deviation on protrusion
If a lesion is present, the tongue deviates to the side of the lesion
There may also be muscle wasting on the side of the lesion and fasiculation (involuntary twitching)
