The Cranial Nerves Flashcards
Importance of testing cranial nerve function
- Localise site of lesions
- Gauge function in unconscious patients
- Can test bilaterally, sensory and motor function
Test: CN I
Damage: fracture of anterior cranial fossa causes anosmia can substantially affect ‘taste’. CSF rhinorrhoea major problem - infection.
- Rarely tested
- Nerves continually replaced
- Close one nostril, ensure airway is clear
- Test detection of smell with non-irritant substance (peppermint/perfume)
Test: CN II
Visual Fields:
- Binocular: cover one eye to test other
- Test: detect moving object (e.g. finger)
- Optic nerve: monocular anopia
- Optic chiasm: bitemporal hemianopia
- E.g. pituitary tumour
- Optic tract: homonymous hemianopia
Simple function: pupillary light reflex
NB: more complex problems can be revealed: e.g. neglect of half the visual field results from contralateral parietal lobe lesion
Test: foveal vision
- Can be affected in macular degeneration & diabetic retinopathy
- Peripheral vision remains, lose fine detail
Test: visual acuity
Snellen chart
Discuss examination of the optic fundi
- Using ophthalmoscope - see optic nerve head & retinal blood vessels
- Papilloedema: enlarged & ‘wooly’ optic disk
- Raised intracranial pressure
Test: CN III
Pupillary light reflex: tests CN II (afferent) & CN III (efferent - parasympathetic):
- Can be tested in unconscious patients
- Shine light in one eye - both pupils should constrict (consensual response)
- Brainstem reflex
- Can be abolished by damage due to raised intracranial pressure or physical stretch
Eyelid innervation
- CN III innervates LPS, sympathetic hitchhiking innervate superior tarsal muscle (raise eyelid)
- Damage to III gives complete ptosis
- Sympathetic loss (e.g. Horner’s) - partial ptosis
Testing CNs III, IV, VI (general)
Extraocular muscles work synergistically
- Inspect eye position at rest
- Look for non-consensual movement/nystagmus
Accommodation/convergence reflex:
- Look in distance then focus on near object
- Eyes converge (medial recti) & pupils constrict
Damage due to brainstem artery aneurysm, cavernous sinus disease, tumours, strokes, raised intracranial pressure
NB: get diplopia & tilting head to compensate
CN III lesion
- Complete ptosis
- Fixed dilate pupil with lack of accommodation
- Inability to look up/medially (down & out)
CN IV lesion & test
- Eye turned medially (adducted)
- Diplopia when looking down
- Test by looking down and in to exclude inferior and lateral rectus
CN VI lesion
- Most commonly damaged
- 1st damaged in raised intracranial pressure
- Squint & diplopia with inability to abduct eye
- Adducted at rest
- Test: ask patient to follow finger moving side to side in horizontal plane
Test: CN V (general)
- Facial sensation, light touch with cotton wool:
- Forehead: Va
- Medial cheek: Vb
- Chin: Vc
-
Corneal reflex: aversive, rapid, involuntary response blink to touching cornea
- Brainstem reflex (Va - nasociliary afferent, VII efferent)
- Herpes zoster can map out divisions
- Damage to roots = anaesthesia over respective areas: anterior scalp, skin, cornea, conjunctiva, mucosa of nose & mouth, general sensation to anterior two-thirds of tongue
Test: CN Vc
- Motor branches to muscles of mastication
- Feel bulk of temporalis/masseter on firm closing
- Open against resistant (lateral pterygoid)
- Damage: tumours (middle CF), stroke
- Deviation to weak side (CL to lesion)
Complications of testing CN V with example
- Many autonomic fibres hitchhike
- S which reach head via blood vessels
- PS emerging with CNs III, VII, IX, X
- E.g. lingual branch (Vc) lesions peripherally can cause loss of taste to anterior 2/3 of tongue & salivation depending on site of lesion
Test: CN VII
Test motor fibres
- Raise eyebrows
- Screw up eyes
- Smile
- Squeeze lips together & blow out cheeks
- Bare teeth
CN VII lesions
Symptoms depend on location:
Stroke (‘upper motorneuron lesion):
- Loss of muscles of facial expression BUT forehead sparing
- Bilateral innervation of frontalis by brain
Bell’s Palsy - inflammation at stylomastoid foramen
- Paralysis of facial muscles, no forehead wrinkles, excessive tear production, dribbling
Lesions in middle ear:
- Affects chorda tympani - loss of taste (ant 2/3) & secretion by sub-lingual/mandibular glands
- Hyperacusis (loss of stapedius)
More proximal in temporal bone: acoustic neuroma
- Dry eyes + the above
Test: CN VIII
Hearing:
- Conductive vs sensorineural deafness
- Rinne’s & Weber test
Balance:
- Postural stability with eyes closed
- Irrigation of ear canal with warm/ice-cold water causes nystagmus
NB: VIII afferents to oculomotor efferents allows both to be tested, in unconscious patients
CN VIII lesion
- Dizziness & nausea
- Vestibulo-ocular reflexes keep eyes pointing in fixed direction when head moves
- Gives Dolls-eye reflex
- Gaze shouldn’t move if head tilted
Test: CNs IX, X, XI
Best considered as a group, damage rarely individual
IX, X:
- Gag reflex: brisk stimulation of posterior tongue/oropharynx - IX afferent, X efferent
- Can be tested in unconscious patients
X:
- Patient says ‘aah’ uvula should move up/down but not deviate from midline
- Coughing tests closing of vocal cords (recurrent laryngeal)
XI:
- Turning head against resistance or shrugging
- Test sternocleidomastoid & trapezius
CNs IX, X, XI lesions
- Inflammation oropharynx/tonsillitis: referred pain to middle ear (CN IX)
- X - affect speech. Cord adducted in partial lesions, in mid-position in complete lesions
- Dysfunction of sensory/motor innervation of larynx/pharynx = major issues for swallowing
- E.g. bulbar palsy
- XI - rarely peripheral, can be neurological
NB: parasymp of X only important if lesion bilateral
Test: CN XII
- Look for wasting/fasciculation of tongue
- Stick out tongue: deviation to side of lesion due to unopposed genioglossus on unaffected side
- Damage most common following stroke
- Central connections bilateral, many cases function recovers after time
- Also vulnerable to tumours & penetrating trauma
Path of CN VII
- Arises as two roots
- Large motor root
- Smaller nervus intermedius (parasympathetic & sensory)
- Enter IAM & join in the facial canal (PTB)
- Turn posteriorly on medial wall of middle ear
- Forms geniculate ganglion
- Runs inferiorly on posterior wall of middle ear
- Exits skull via stylomastoid foramen
- Enters parotid giving its terminal branches
Branches of VII in middle ear
- Greater petrosal nerve (geniculate ganglion)
- Parasympathetic to lacrimal gland (via PPG)
- Nerve to stapedius
- Dampens vibrations
- Chorda tympani (to tongue via lingual n.)
- Taste & parasympathetic to submandibular & sublingual glands
Branches of VII before parotid gland
- Nerve to occipitalis
- Nerve to stylohyoid
- Nerve to posterior belly of digastric
Branches of VII in parotid gland
- Temporal
- Frontalis, orbicularis oculi
- Zygomatic
- Muscles of eyelid
- Buccal
- Buccinator, orbicularis oris, muscles of external nose
- Mandibular
- Muscles of lower lip & chin
- Cervical
- Platysma
Describe CN II
Optic nerve - purely sensory, path:
- Axons originate from the retinal cells
- Partial decussation at optic chiasma
- Optic tracts continue to LGN
NB: CN II is an outgrowth of the brain ⇒ covered in meningeal layers which pierce sclera.
A small subarachnoid space means increased intracranial pressure is visualised by papilloedema
Path of CN III
- Exits midbrain, pierces roof of cavernous sinus
- Runs in lateral wall of sinus
- Splits into two divisions when leaving sinus
- Superior division (SOF): LPS, superior rectus
- Inferior division (tendinous ring): rest
Discuss the parasympathetic fibres of CN III
- For ciliary muscles and sphincter pupillae
- Carried in inferior division
- Fibres leave to reach ciliary ganglion
- Post-ganglionic leave as short ciliary nerves
Nerves running in the cavernous sinus
Lateral wall:
- III, IV, Va
NB: VI runs in sinus, lateral to ICA
Path of CN V
- Leaves brainstem as two roots (sensory & motor)
- Sensory is larger, cell bodies form trigeminal ganglion (branches come from ant edge)
- Motor root is smaller, joins Vc
- Pass forwards under tentorium cerebelli through oval opening in dura mater at trigeminal impression (apex of PTB)
Branches of Va
- Frontal: skin on forehead & ant. 1/2 of scalp
- 2 branches: supratrochlear & supraorbital
- Lacrimal: skin of upper eyelid
- Carry PS fibres: PPG → lacrimal ganglion
- Nasociliary: ethmoidal & sphenoidal sinuses, root of the nose
- Gives long ciliary nerves:
- Sensation to cornea
- Sympathetics to dilator pupillae
- Gives long ciliary nerves:
NB: Va distributes sympathetic fibres from internal carotid plexus to vessel, orbit, sweat glands of forehead & dilator pupillae
Branches of Vb
- Zygomatic: skin of lateral forehead & cheek
- 2 branches: zygomaticotemporal & zygomaticotemporal
- Ganglionic: branches to PPG
- Infraorbital: maxillary teeth
Sensory branches of Vc
- Buccal: mucous membrane/skin of cheek
- Auriculotemporal: TMJ, skin of upper 1/2 ear, EAM, scalp above EAM
- Inferior alveolar: mandibular teeth
- Mental nerve: skin of lower lip
- *motor fibres: nerve to mylohyoid
- Mylohyoid & anterior belly of digastric
- Lingual: ant. 2/3 of tongue, floor of mouth
- Sensory fibres → submandibular ganglion
- Joined by chorda tympani
Motor branches of Vc
- N. to medial pterygoid
- + tensor tympani & tensor palati
- Deep temporal n.
- N. to lateral pterygoid
- N. to masseter
Sensory distribution of V on the face
CN I summary
- Olfactory nerve
- Cribriform plate
- Special sensory - smell
CN II summary
- Optic nerve
- Optic canal
- Special sensory - vision
CN III summary
- Oculomotor nerve
- Superior orbital fissure
Somatomotor:
- LPS, S/M/I recti, inferior oblique
Visceromotor:
- PS to ciliary muscle & sphinctoer pupillae
CN IV summary
- Trochlear nerve
- Superior orbital fissure
- Somatomotor: superior oblique
Va summary
- Ophthalmic branch of the trigeminal nerve
- Superior orbital fissure
Somatosensory:
- Skin of forehead, ant. 1/2 scalp & upper eyelid
- Cornea
- Ethmoidal & sphenoidal sinuses, & root of nose
Vb summary
- Maxillary branch of the trigeminal nerve
- Foramen rotundum
Somatosensory:
- Skin of lateral forehead & cheek
- Maxillary teeth
Vc summary
- Mandibular branch of the trigeminal nerve
- Foramen ovale
Somatosensory:
- Mucous membrane/skin of cheek & lower lip
- TMJ, upper 1/2 ear, EAM, scalp above EAM
- Mandibular teeth
Branchiomotor:
- Muscles of mastication
CN VI summary
- Abducent nerve
- Superior orbital fissure
- Somatomotor: lateral rectus
CN VII summary
- Facial nerve
- Internal auditory meatus/stylomastoid foramen
Somatosensory:
- Ear & tympanic membrane
Special sensory:
- Taste to the anterior 2/3 of the tongue
Branchiomotor:
- Muscles of facial expression
Visceromotor:
- PS to all glands of H/N except parotid
CN VIII summary
- Vestibulocochlear nerve
- Internal auditory meatus
- Special sensory: hearing and balance
CN IX summary
- Glossopharyngeal nerve
- Jugular foramen
Somatosensory:
- Posterior 1/3 of tongue, internal surface of tympanic membrane
Viscerosensory:
- Pharynx, carotid body
Special sensory:
- Taste to posterior 1/3 of tongue
Visceromotor:
- Parasympathetics to parotid gland
CN X summary
- Vagus nerve
- Jugular foramen
Somatosensory:
- External ear
Viscerosensory:
- Larynx & viscera
Special sensory:
- Taste to epiglottis and valleculae
Branchiomotor:
- Muscles of pharynx & larynx
Visceromotor:
- PS to neck, thorax and abdomen
CN XI summary
- Spinal accessory nerve
- Jugular foramen
- Somatomotor: trapezius & sternocleidomastoid
CN XII summary
- Hypoglossal nerve
- Hypoglossal canal
- Somatomotor: muscles of tongue except palatoglossus
