13. Neurology II: Cranial nerves & their disorders Flashcards
cranial nerves
- how many?
- form PNS or CNS?
- sensory or motor supply?
– 12 cranial nerves
– Part of the peripheral nervous system (PNS)
– Primarily sensory and/or motor supply to the head and neck
dental relevance of cranial nerves
- Innervation to all head and neck structures of relevance to dentists
- Cranial nerve pathology may be detected during routine dental examination, or patients may present with symptoms
- If you suspect cranial nerve pathology, ensure there is appropriate medical follow-up (e.g. usually via GP, A&E for emergencies)
what are the 12 cranial nerves?
I Olfactory
II Optic
III Occulomotor
IV Trochlear
V Trigeminal
VI Abducens
VII Facial
VIII Vestibulocochlear
IX Glossopharyngeal
X Vagus
XI Accessory
XII Hypoglossal
HINT
PNEUMONIC TO HELP REMEMBER
On On On They Travelled And Found Voldemort Guarding Very Ancient Horcruxes
OLd OPie OCcasionally TRies TRIGonometry And Feels VEry GLOmy, VAGUe, And HYPOactive
which cranial nerves are sensory, motor or both?
I Olfactory some
II Optic say
III Occulomotor marry
IV Trochlear money
V Trigeminal but
VI Abducens my
VII Facial brother
VIII Vestibulocochlear says
IX Glossopharyngeal big
X Vagus brains
XI Accessory matter
XII Hypoglossal more
KEY
S = sensory
M = motor
B = both
CRANIAL NERVE I
1
myelinated or unmyelinated?
2
key features
3
function
4
causes of damage
5
damage results in
6
how to test olfactory nerve
OLFACTORY
1
unmyelinated
2
- Shortest cranial nerve
- Specialised epithelium at the top of the nasal cavity contains olfactory nerve fibres
3
- sense of smell
4
Causes include head injuries, tumours and neurodegenerative disorders
5
- Damage to the olfactory nerve can cause altered sense of smell, or complete loss of sense of smell (anosmia)
- Temporary changes to smell can be caused by infection
6
1. Ask about any recent changes to sense of smell
2. 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 side.
CRANIAL NERVE II
1
function
2
causes of defects
3
how to test
OPTIC
1
transmission of sensory information from the retina to the primary visual cortex of the brain
2
– Trauma
– Tumour (e.g. pituitary adenoma)
– Multiple sclerosis (optic neuritis)
– Stroke
3
Examination includes testing the following:
- 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).
- In a dental setting, fundoscopy is rarely performed; however visual acuity, visual fields and reflexes can be performed easily
CRANIAL NERVE II
how is visual acuity test performed?
- VISUAL ACUITY
Formal
- Snellen chart with the patient sat 6 metres away
- Colour vision is also assessed using Ishihara plates
Dental setting
- Ask the patient to read from a printed page (glasses, contact lenses should be worn)
- Test one eye at a time
CRANIAL NERVE II
how is visual fields test performed?
- Tested through confrontation
- Assumes that the examiner has normal visual fields
CRANIAL NERVE II
how is pupillary reflex test performed?
Darkened room
1.Direct reflex – shine pen torch into one eye. Look for pupillary constriction of ipsilateral eye (i.e. the eye you are shining the light into)
2.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
Other tests performed in a medical setting: accommodation, swinging light test
CRANIAL NERVE II
Examples of nerve defects?
Left optic nerve lesion
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)
Left oculomotor nerve lesion:
Shine a pen torch into the left
eye:
- Left direct reflex lost
- Left consensual reflex lost
- Right direct reflex maintained
- Right consensual reflex
maintained
CRANIAL NERVE III / IV / VI
what do they supply
III Oculomotor nerve
IV Trochlear nerve
VI Abducens nerve
often assessed together
1
- supply the extra-ocular muscles
III = supplies medial, superior & inferior rectus, inferior oblique, levator palpebrae superioris, also supplies parasympathetic
fibres involved in pupillary constriction
IV = supplies superior oblique
VI = supplies lateral rectus
Remembered using the formula:
SO4LR6
CRANIAL NERVE III / IV / VI
1
what will palsies of III, IV, VI result in?
2
causes of palsy and what happens?
1
diplopia (double vision)
2
III
- CAUSE: diabetes, increased intra-cranial pressure
- HAPPENS: Eye is fixed down and out, unless looking towards the affected side
Additional signs: ptosis, dilated pupil (mydriasis)
IV
CAUSE: trauma
HAPPENS: Eye cannot move down and in (vertical diplopia when looking inferiorly)
VI
CAUSE: stroke, multiple sclerosis
HAPPENS: Cannot look to the affected side
CRANIAL NERVE III / IV / VI
How to test?
- Usually performed alongside cranial nerve II, after visual fields
- Ask patient to follow a pen as you draw out the letter H
- Ensure they keep the head still and only move the eyes
- smooth symmetrical movement of eyes
CRANIAL NERVE V
1
causes of nerve palsy?
TRIGEMINAL NERVE
1
- 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
CRANIAL NERVE V
how to test
TRIGEMINAL NERVE
SENSORY
- Sensory component divided into
ophthalmic (V1), maxillary (V2) and
mandibular (V3) divisions
- Tested through light touch and pin
prick (use a Neurotip)
- test touch on each subregion of CNV
- Corneal reflex (V1) not routinely
tested
- sensory to tongue
MOTOR
- 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)
CRANIAL NERVE VII
function?
FACIAL NERVE
SENSORY = for taste to the anterior 2/3rds via chorda tympani
MOTOR = muscles of facial expression, nerve to stapedius
SECRETOMOTOR to lacrimal, submandibular & sublingual salivary glands.
CRANIAL NERVE VII
1
causes of nerve palsy
2
how to test?
FACIAL NERVE
1
- 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)
(maybe go over anatomy)
2
- Ask about changes to sense of taste
- Ask about hearing (hyperacusis) (maybe louder with bells palsy)
- Facial movements (tested against resistance)
- Raise eyebrows, close eyelids, puff out cheeks
purse the lips, show your teeth
CRANIAL NERVE VIII
1
function
2
causes of nerve defects
3
testing
VESTIBULOCOCHLEAR NERVE
1
- sensory function
- Involved in hearing + balance
2
- acoustic neuroma
- Paget’s disease
3
- Ask about changes to hearing
- Whisper into the ear (choose a bi-digit number or two syllable word) and ask the patient to repeat
- in the other ear crumple a paper or something to make sure they’re only listening from 1 ear
- Rinne and Weber test are performed using a tuning fork to assess for sensorineural vs conductive deafness
CRANIAL NERVE IX
1
function
2
causes of nerve palsy
3
testing
GLOSSOPHARYNGEAL NERVE
1
- Sensory and motor functions
- Principle role is sensory to tonsillar fossa and pharynx
- taste to the posterior 1/3rd of the tongue
- parasympathetic innervation to the parotid glands
2
- trauma
- tumour
- diphtheria
- (IX nerve problems usually occur alongside CN X problems)
3
- IX + X are usually tested together
- Patients with IX nerve palsy will have impaired gag reflex
- Testing the gag reflex is not routinely performed
CRANIAL NERVE X
1
function
2
causes of nerve palsy
3
testing
VAGUS NERVE
1
- Motor function supplying:
~ pharynx
~ larynx
~ soft palate
2
- trauma
- brainstem lesion
3
- 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)
NB The vagus nerve has other important functions, including visceral sensation of the heart, and parasympathetic innervation of the gastrointestinal tract and heart rhythm.
CRANIAL NERVE XI
1
function
2
causes of nerve palsy
3
testing
ACCESSORY NERVE
(also known as spinal accessory nerve)
1
- Motor function to muscles of neck
2
- stroke
3
- Inspect for wasting of trapezius/ sternocleidomastoid
- Shrug shoulder against resistance (test one side at a time)
- Turn the head against resistance
CRANIAL NERVE XII
1
function
2
causes of nerve palsy
3
testing
HYPOGLOSSAL NERVE
1
- Motor function to the tongue
2
- trauma
- brainstem lesions
3
- 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)
extra info
Performing a Cranial Nerve Examination
- Within a dental setting we tend to perform an abbreviated form of the cranial nerve
examination (e.g. the eye examination is not as in depth as in a medical setting)
- Practice is important as there is a lot to remember (practice with each other initially so
that you do things correctly. Once you have a clear idea of the structure, recruit friends
and relatives to practice with to improve your fluency)
- Online videos can be useful, but may contain errors. The links below are not perfect, but
are some of the better examples of free online videos
- University of Leicester https://www.youtube.com/watch?v=jdaq-Ecz7Co
- Geeky Medics https://geekymedics.com/cranial-nerve-exam/
- Macleod’s Clinical Examination is a textbook that provides excellent examination
videos (check the library). They are much more detailed than you need, but everything
is performed correctly.
