Cranial nerves and their assessment Flashcards
Cranial nerves
12 pairs
Part of peripheral NS
Some sensory, motor or mixed
Some have autonomic functions (III, VII, IX, X)
Except for vagus (X), all others serve only structures in head and neck
Where do the cranial nerves originate from?
I and II from pons
V - VII originate from medulla
IX and XII originate from medulla
Sensory motor mixed pnemonic
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Cranial nerves in order
Olfactory Optic Oculomotor Trochlear Trigeminal Abducens Facial Acoustic Glossopharyngeal Vagus Accessory Hypoglossal
Olfactory nerve
- function
- origin and destination
CN I
Sense of smell
Arises from receptor cells in the nasal epithelium
Travels via olfactory nerve filaments through the cribiform plate of ethmoid bone to the olfactory cerebral cortex (especially temporal lobe)
Responsible for sense of smell
Damage to olfactory nerve
Causes impaired sense of smell
Testing olfactory nerve
Not tested routinely
Ask if any change in sense of smell or taste
If testing indicated
-get pt to clear nose
-ask pt to hold one nostril closed and close eyes
-place recognisable scent under nostril (e.g. coffee, peppermint, lemon, vanilla, chocolate)
Repeat with other nostril
Nb. avoid irritating substance like vinegar - these may stimulate pain receptors of trigeminal nerve
Anosmia
Loss of sense of smell (e.g. flu, nasal polyps)
Most commonly results from nasal congestion
Other causes are
-basal or frontal skull fracture
-nasal or frontal lobe (olfactory groove) tumour
CN I lesion
Nose, cribiform plate of ethmoid bone, base of skull
E.g. meningioma, early sign of Parkinson
The optic nerve
- function
- origin and destination
CN II
Provides vision
Sensory
From retinal euro-epithelium
-rods and cones activate bilpolar cells (first order neurones)
-synapsing on ganglion cells in retina
To: second order neurones converge on optic disc/ where optic nerve partially crosses over at optic chiasma to opposite side of brain
Interpretation of vision (central and peripheral) occurs in occipital cortex
Damage to the optic nerve
Damage causes blindness in visual field
Testing optic nerve
- Visual acuity: central vision (Snellen chart)
- position pt 6m from chart
- pt covers one eye at time
- record smallest line
- record as fraction: upper (1st) number normally 6 (m away from chart), lower (2nd) number tiny number under smallest line read - Peripheral vision
- sit arms length and at eye level
- aim of test to compare your vision with pts
- to check left eye, pt covers right eye with card and you do to, ask pt to look directly into your eye
- move your wagging finger from periphery towards centre and ask pt to tell you when their finger moves
- should be tested in horizontal plane and in upper and lower temporal quadrants
- change hands and repeat on nasal side - Fundoscopy
- pt gazes into distance
- look at cornea (for ulcers), iris and then lens for red reflex (absent if pt has cataracts)
- search for optic disc by following large retinal vein back towards disc, where they all converge
- look at edges of disc and colour - Light reflex
- shine light in one eye (stimulate optic nerve) and both pupils constrict (both oculomotor nerves)
Cranial nerve III, IV and VI
Controls eye movement and are tested together
III: oculomotor nerve
IV: trochlear nerve
VI: abducen nerve
All have sensory component for muscle proprioception
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Oculomotor nerve
Somatic and autonomic motor function
Eye movement, opening of eyelid, focusing
Muscles it controls:
Medial rectus (looking inwards)
Superior rectus (looking upwards)
Inferior oblique (looking upwards and inwards)
Inferior rectus (looking downwards)
Trochlear nerve
-function
-damage and causes
Origin and destination
Eye movement:
Superior oblique (downwards and inwards)
Mixed nerve fibres, mainly motor
Originates from midbrain and travels alongside oculomotor nerve to supply SO muscle
Damage causes double vision on looking straight down and inability to rotate eye laterally
Causes:head injuries, aneurysms of internal carotid artery
Abducens nerve
- function
- damage and causes
Provides eye movement:
Lateral rectus (outwards)
Damage results in inability to rotate eye laterally and at rest eye rotates medially
Causes: head injuries, aneurysms of internal carotid artery
Complete and partial 3rd nerve palsy
- symptoms
- causes
Symptoms:
-ptosis
-eyes down and out
-failure of adduction
Causes:
-complete palsy commonly caused by compressive lesion
-partial III nerve palsy spares pupil (vascular link, diabetes mellitus, aneurysm, tumour, trauma)
Common causes of abnormal eye movements
Central (brainstem) lesions Vascular e.g. basilar thrombosis, pontine haemorrhage Tumour e.g. pontine glioma Demyemlination Wernickes Encephalopathy Peripheral Lesions Vascular e.g. hypertension Basal skull fracture Vasculitis GBS (Miller-Fisher variant) Complete Opthalmoplegias Thyroid eye disease, myasthenia Gravis, myopathies.
Six cardinal positions of gaze ‘H’ test conjugation
For extraocular movements
This test examines the six positions in which the eye moves
Tell pt to hold their head still and to follow a pen with their eyes as you move it
Assess for eye movement, diplopia (double vision) and nystagmus (involuntary eye movement)
-diplopia is early sign of ocular muscle weakness
Branches of trigeminal nerve
Sensory branch -ophthalmic (V1) -maxillary (V2) -mandibular (V3) Motor branch -muscles of mastication (temporalis, masseter, medial pterygoid, lateral pterygoid) -tensor veli palatine -mylohyoid -anterior belly of digastric -tensor tympani Nb: all muscles involved in biting, chewing, swallowing except for tensor tympani which acts to dampen sound produced from chewing
Testing trigeminal nerve (sensory)
Test for soft touch using cotton wool V1 - ophthalmic - forehead up to top of head V2 - maxillary V3 - mandibular - up to angle of jaw The pt should be instructed to say 'yes' each time touch of cotton wool is felt Do not stroke skin, touch it Test for pain using sharp object -ask pt does it feel sharp or dull
Causes of sensory problems to trigeminal nerve
MS - MS plaque in brainstem in young people
Sjogren - dry eyes, dry mouth
Trigeminal neuralgia - older people
Testing corneal reflex
Ask pt to look up and away, touch cornea with cotton bud
-blinking of both eyes is normal response
(trigeminal nerve)
Corneal pathology
Bell’s palsy: unable to blink due to damage to efferent limb (CN VII)
CN V forms afferent limb
Testing motor function of trigeminal nerve
Inspect for wasting of temporal and masseter muscles
Ask pt to clench teeth and palpate for contraction of temporal and masseter muscles
Ask pt to open mouth and hold it open whilst examiner attempts to force it shut (pterygoid muscles)
Unilateral weakness of motor division causes jaw to deviate towards one side
-if weakness suspected pts should be asked to move jaw laterally against resistance
-jaw can be moved towards affected muscle but cannot move towards normal side
The jaw jerk
The jaw jerk
Ask the pt to open her mouth fully, and close halfway, place index finger on her chin and tap with a patella hammer, if jaw jerk is highly exaggerated.
Help to distinguish btw pseudobulbar palsy (UMN lesion of lower cranial nerve 9, 10,11,12) and a bulbar palsy (LMN lesion of lower cranial nerve 9,10,11,12)
The facial nerve
- functions
- damage
Somatic Motor - facial expressions.
Autonomic Motor - salivary and lacrimal glands, mucous membranes of nasal and palatine mucosa.
Special Sensory - taste on anterior 2/3’s of tongue.
Damage produces sagging facial muscles and disturbed sense of taste (no sweet and salty)
Components of facial nerve
- Branchial motor
-from facial nerve nucleus
-through petrous temporal bone, internal auditory meatus, geniculate ganglion, facial canal (tortuous course) –> stylomastoid foramen (except stapedius)
-stylomastoid foramen to major facial branches; posterior auricular nerve (controls scalp muscles around ear), posterior belly of digastric, stylohyoid muscle
From nevus intermedius through geniculate ganglion: - Parasympathetic
-greater petrosal to lacrimal gland, sphenoid sinus, frontal sinus, maxillary sinus, ethmoid sinus, nasal cavity - Sensory
-small contribution to external acoustic meatus - Taste
-palate via greater petrosal
-anterior 2/3 tongue via chorda tympani
Major facial branches
Temporal: frontalis, orbicularis oculi Zygomatic -Z1: eye and around orbit -Z2: mid face and smile Buccal: buccinator, upper lip Mandibular: lower lip, orbicularis oris Cervical: platisma
Testing facial nerve: motor
- Ask pt to shut eyes tightly
Observe and try to force open each eye
If lower motor neuron lesion detected [weakness on one side of face], check for ear and palatal vesicles of herpes zoster of geniculate ganglion – Ramsay Hunt syndrome - Ask pt to look up and wrinkle forehead. Feel for muscle strength by pushing down on forehead.
This movement is preserved on side of an upper motor neurone lesion [a lesion which occurs above the level of the brainstem nucleus], because of bilateral supranuclear innervation giving some compensation to the upper face which is not the case in LMN lesion (Bells palsy/Ramsay Hunt- Herpes Zoster)
Remaining muscles of facial expression usually affected on the side of an UMN lesion.In a LMN lesion all muscles of facial expression are affected on the side of the lesion. - Ask pt to show their teeth
Compare nasolabial grooves which are smooth on the weak side.
Left upper motor neuron seventh nerve lesion leads to drooping of the corner of the mouth, flattened nasolabial fold, and sparing of the forehead on the left side** - Ask pt to blow out cheeks
Clinical features of LMN lesions
Bells Palsy Ramsey Hunt Syndrome Acoustic neuroma Sarcoid GBS, Myasthenia Myotonic Dystrophy
Clinical features of UMN lesions
CVA
MDB, Pseudobulbar palsy
Vestibular/ cochlear nerve
- function
- damage
CN VIII
Special Sensory
Provides hearing (cochlear branch) and sense of balance (vestibular branch)
Damage produces deafness, dizziness, nausea, loss of balance and nystagmus
Testing vestibulocochlear nerve
Hearing and balance
Any problem with hearing? Hearing aids?Mask- cover the tragus of the ear and whisper a number, ask pt to repeat
If deafness suspected perform Rinne’s test and Weber’s test
Rinne’s test
base of tuning fork (256 Hz ) on the mastoid process,
“tell me when it stops”,
then bring it to the ear,
“Can hear it? “
With nerve deafness the note is audible at the external meatus, as air and bone conduction are reduced equally, so that air conduction is better as is normal. This is termed Rinne-positive.With conduction [middle ear] deafness no note is audible at the external meatus. This is termed Rinne-negative.
Weber’s test
A vibrating tuning fork is placed on the centre of the forehead. Normally the sound is heard in the centre of the forehead. With nerve deafness the sound is transmitted to the normal ear. With conduction deafness the sound is heard louder in the abnormal ear.
Pts with defective hearing should be referred for audiometry. This measures the degree of hearing loss at different sound frequencies
Glossopharyngeal nerve
-functions
CN IX
Somatic motor – Swallowing and voice production using pharyngeal muscles
Autonomic motor - salivation, gagging, control of BP and respiration
Sensations from posterior 1/3 of tongue, tonsils and parts of pharynx
Sensations from baroreceptors and chemoreceptors
Vagus nerve
CN X
Testing CN IX and X
Uvula:
Get the patient to open their mouth and inspect the palate with a torch. Note any displacement of the uvula.
Ask the patient to say ‘Ah’. If the uvula is drawn to one side this indicates a unilateral tenth nerve palsy. The uvula is pulled towards the normal side.
Now test gently for the gag reflex
Ninth is the sensory component
Tenth is the motor component
Gag reflex:
Touch the back of the pharynx on each side with a spatula. Ask the patient if the touch of the spatula is felt each time. Normally there is reflex contraction of the soft palate.
The ninth nerve supplies taste from the posterior two-thirds of the tongue this is not routinely tested for.
Clinical features of damage to CN IX / X
Failure of palatal movement increases the risk of aspiration.
Ask patient to open mouth and say aah! .. if uvula is drawn to one side = 10th nerve palsy.
Damage causes hoarseness or loss of voice, impaired swallowing, GI dysfunction, blood pressure anomalies (with CN IX), fatal if both are cut
Causes of damage to CN IX and CN X
Lateral Medullary syndrome: sensory loss in face (same side) and body (opposite). Same side cerebellar signs and Horner’s sign
Jugular Foramen Syndrome
Progressive Bulbar Palsy (MND)
Accessory nerve functions
CN XI
Involved with swallowing, head, neck and shoulder movement via trapezius, sternocleidomastoid and pharyngeal muscles
Teting accessory nerve
Trapezius:
Ask the patient to shrug their shoulders and feel the bulk of the trapezius muscles and attempt to push the shoulders down
Sternocleidomastoid:
Ask pt to turn their head against resistance and feel the bulk of the sternomastoids. Feel for the sternomastoid on the side opposite to the turned head. There will be weakness on turning the head away from the side of a muscle whose strength is impaired.
(Optional)Test neck flexors if suspect myasthenia gravis, MND-
“put chin on chest, I’ll put my hand onto your forehead, push up against my hand”
Hypoglossal nerve
- function
- damage
Tongue movements for speech, food manipulation and swallowing.
If both are damaged – can’t protrude tongue.
If one side is damaged – tongue deviates towards injured side
Testing motor hypoglossal
Observe the tongue at rest- wasting? on one side? fasciculation?
Stick out tongue straight- deviate to one side?
Tongue deviate to the side of a lesion of CNXII
Wiggle tongue side-to-side - (coordination)altered in cerebellar disorder
