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2 - HNA > The Cranial Nerves > Flashcards

The Cranial Nerves Flashcards

1
Q

Importance of testing cranial nerve function

A
  • Localise site of lesions
  • Gauge function in unconscious patients
  • Can test bilaterally, sensory and motor function
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2
Q

Test: CN I

A

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)
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3
Q

Test: CN II

A

Visual Fields:

  • Binocular: cover one eye to test other
  • Test: detect moving object (e.g. finger)
  1. Optic nerve: monocular anopia
  2. Optic chiasm: bitemporal hemianopia
    • E.g. pituitary tumour
  3. 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

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4
Q

Test: foveal vision

A
  • Can be affected in macular degeneration & diabetic retinopathy
  • Peripheral vision remains, lose fine detail
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5
Q

Test: visual acuity

A

Snellen chart

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6
Q

Discuss examination of the optic fundi

A
  • Using ophthalmoscope - see optic nerve head & retinal blood vessels
  • Papilloedema: enlarged & ‘wooly’ optic disk
    • Raised intracranial pressure
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7
Q

Test: CN III

A

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
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8
Q

Eyelid innervation

A
  • 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
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9
Q

Testing CNs III, IV, VI (general)

A

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

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10
Q

CN III lesion

A
  • Complete ptosis
  • Fixed dilate pupil with lack of accommodation
  • Inability to look up/medially (down & out)
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11
Q

CN IV lesion & test

A
  • Eye turned medially (adducted)
  • Diplopia when looking down
  • Test by looking down and in to exclude inferior and lateral rectus
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12
Q

CN VI lesion

A
  • 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
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13
Q

Test: CN V (general)

A
  • 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
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14
Q

Test: CN Vc

A
  • 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)
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15
Q

Complications of testing CN V with example

A
  • 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
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16
Q

Test: CN VII

A

Test motor fibres

  • Raise eyebrows
  • Screw up eyes
  • Smile
  • Squeeze lips together & blow out cheeks
  • Bare teeth
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17
Q

CN VII lesions

A

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
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18
Q

Test: CN VIII

A

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

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19
Q

CN VIII lesion

A
  • 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
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20
Q

Test: CNs IX, X, XI

A

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
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21
Q

CNs IX, X, XI lesions

A
  • 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

22
Q

Test: CN XII

A
  • 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
23
Q

Path of CN VII

A
  1. Arises as two roots
    • Large motor root
    • Smaller nervus intermedius (parasympathetic & sensory)
  2. Enter IAM & join in the facial canal (PTB)
  3. Turn posteriorly on medial wall of middle ear
    • Forms geniculate ganglion
  4. Runs inferiorly on posterior wall of middle ear
  5. Exits skull via stylomastoid foramen
  6. Enters parotid giving its terminal branches
24
Q

Branches of VII in middle ear

A
  1. Greater petrosal nerve (geniculate ganglion)
    • Parasympathetic to lacrimal gland (via PPG)
  2. Nerve to stapedius
    • Dampens vibrations
  3. Chorda tympani (to tongue via lingual n.)
    • Taste & parasympathetic to submandibular & sublingual glands
25
Branches of VII before parotid gland
1. Nerve to occipitalis 2. Nerve to stylohyoid 3. Nerve to posterior belly of digastric
26
Branches of VII in parotid gland
1. Temporal * Frontalis, orbicularis oculi 2. Zygomatic * Muscles of eyelid 3. Buccal * Buccinator, orbicularis oris, muscles of external nose 4. Mandibular * Muscles of lower lip & chin 5. Cervical * Platysma
27
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
28
Path of CN III
1. Exits midbrain, pierces roof of cavernous sinus 2. Runs in lateral wall of sinus 3. Splits into two divisions when leaving sinus 1. Superior division (SOF): LPS, superior rectus 2. Inferior division (tendinous ring): rest
29
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
30
Nerves running in the cavernous sinus
Lateral wall: * III, IV, Va NB: VI runs in sinus, lateral to ICA
31
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)
32
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 NB: Va distributes sympathetic fibres from internal carotid plexus to vessel, orbit, sweat glands of forehead & dilator pupillae
33
Branches of Vb
* Zygomatic: skin of lateral forehead & cheek * 2 branches: zygomaticotemporal & zygomaticotemporal * Ganglionic: branches to PPG * Infraorbital: maxillary teeth
34
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
35
Motor branches of Vc
* N. to medial pterygoid * *+ tensor tympani & tensor palati* * Deep temporal n. * N. to lateral pterygoid * N. to masseter
36
Sensory distribution of V on the face
37
CN I summary
* Olfactory nerve * Cribriform plate * Special sensory - smell
38
CN II summary
* Optic nerve * Optic canal * Special sensory - vision
39
CN III summary
* Oculomotor nerve * Superior orbital fissure Somatomotor: * LPS, S/M/I recti, inferior oblique Visceromotor: * PS to ciliary muscle & sphinctoer pupillae
40
CN IV summary
* Trochlear nerve * Superior orbital fissure * Somatomotor: superior oblique
41
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
42
Vb summary
* Maxillary branch of the trigeminal nerve * Foramen rotundum Somatosensory: * Skin of lateral forehead & cheek * Maxillary teeth
43
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
44
CN VI summary
* Abducent nerve * Superior orbital fissure * Somatomotor: lateral rectus
45
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
46
CN VIII summary
* Vestibulocochlear nerve * Internal auditory meatus * Special sensory: hearing and balance
47
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
48
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
49
CN XI summary
* Spinal accessory nerve * Jugular foramen * Somatomotor: trapezius & sternocleidomastoid
50
CN XII summary
* Hypoglossal nerve * Hypoglossal canal * Somatomotor: muscles of tongue *except palatoglossus*

2 - HNA (11 decks)

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