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Head and Neck > Cranial nerves I - VI > Flashcards

Cranial nerves I - VI Flashcards

1
Q

What do the cranial nerves supply?

A

Tissues and structures of the head and neck region including special sense organs (eyes, ears, nose, balance)

Except vagus nerve - supplies other parts of body

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2
Q

What system are cranial nerves apart of?

A

Peripheral nervous system

(apart from cranial nerves I and II as these are extension of brain)

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3
Q

How do cranial nerves arise? Is there just one?

A

Arise in pairs - one L and R

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4
Q

What are most cranial nerves associated with?

A

The brainstem (this is where their nuclei are)

Cranial nerves I and II are extensions of brain so exception

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5
Q

What types of fibres can cranial nerves contain?

A

Can be mixed - motor and sensory

Just sensory

Just motor

Parasympathetic (NEVER sympathetic)

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6
Q

3 places cranial nerves can be damaged and cause dysfunction

A

Cranial nerve during route outside brainstem

The brainstem (where cranial nerve nuclei are located)

Neurones within forebrain/brainstem which connect the brain to cranial nerves

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7
Q

How to remember how many cranial nerves arise from where

A

2, 2, 4, 4:

2 CN arise from forebrain
2 CN arise from midbrain
4 CN arise from pons
4 CN arise from medulla

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8
Q

Which CN’s arise from where?

A

CN I and II - forebrain (olefactory and optic)

CN III and IV - midbrain
(oculomotor and trochlear)

CN V, VI, VII and VIII - pons
(trigeminal, abducens, facial and vestibulocochlear)

CN IX, X, XI and XII - medulla
(glossopharyngeal, vagus, spinal accessory nerve and hypoglossal)

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9
Q

What is CN I function

A

Sense of smell - olefactory nerve

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10
Q

How to assess CN I

A

Not routinely tested, if you do test one nostril at a time

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11
Q

What is absence or reduced sense of smell known as?

A

Anosmia or hypo-anosmia

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12
Q

Causes of damage to CN I - olefactory

A

Head/facial injury - impact can stretch/tear olefactory nerves as pass through cribiform foramina

Anterior cranial fossa tumours - compress bulb/tract

Parkinsons/Alzheimers early presentation

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13
Q

Most common cause for anosmia

A

Common cold/upper respiratory tract infection

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14
Q

Where do olefactory nerves travel to perceive smell?

A

Temporal lobe

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15
Q

How does smell travel to brain

A

Olfactory mucosa - olfactory receptors within epithelia of superior nasal cavity
–>
Through skull via cribiform foramina
–>
Olfactory bulb
–>
Olfactory tract
–> T
emporal lobe

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16
Q

What is CN II function? (optic)

A

Special sense vision
Afferent (sensory) arm of pupillary light reflex

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17
Q

What is the special thing about CN II and its extensions?

A

Carries extension of meninges
This CN can be affected by raised intracranial pressure

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18
Q

How to assess CN II?

A

Pupillary size and response to light (CN II forms sensory/afferent limb to CNS for pupillary light reflex)

Visual acuity (clarity) using Snellen chart (optician chart)

Visual fields

Ophthalmoscopy - view anterior optic nerve

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19
Q

What symptoms are associated with CN II (optic) lesions?

A

Blurred vision or absence of vision in eye supplied by CN II

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20
Q

Clinical examination findings for CN II lesion

A

Poor visual acuity (Snellen chart)

Abnormalities in pupil size and response to light

Evidence of pathology when viewing optic nerve on ophthalmoscopy

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21
Q

How else can patients experience the same signs/symptoms as CN II lesion?

A

Lesion can be anywhere along visual pathway - CN II is only small part of this. Pathology can even affect eyeball itself

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22
Q

Diseases of optic nerve

A

Optic neuritis

Anterior ischaemic optic neuropathy (blood supply to anterior optic nerve is disturbed, get ischaemia)

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23
Q

Changes in appearance of optic nerve CN II on ophthalmoscopy

A

Swollen optic disc
If due to raised ICP = Papilloedema

Pale optic disc - can happen following neuritis

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24
Q

What forms the optic nerve?

A

Retinal ganglion cell axons

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25
Q

Route of optic nerve

A

RGC axons form optic nerve

Exits back of orbit via optic canal

Fibres from L and R merge to form optic chiasm

Form L and R optic tracts

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26
Q

What do the fibres from the optic tracts go on to do?

A

Some fibres communicate from tract to brainstem (give info about light sensitivity and control pupil size)

The rest continue along the visual pathway

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27
Q

How does the optic nerve enter the skull?

A

Via optic canal

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28
Q

Where does the visual pathway extend to?

A

From retina back towards primary visual cortex in occipital lobe

29
Q

Why do the optic tracts communicate with the brainstem?

A

Allow for visual reflexes - pupillary reflexes to light

30
Q

What is optic chiasm near? What does this mean?

A

Pituitary gland - pituitary tumours can compress optic chiasm causing bilateral visual symptoms

31
Q

Example of bilateral visual symptom seen in optic chiasm compression from pitiutary tumour

A

Bitemporal hemianopia (loss of visual field, tunnel vision)

32
Q

What does the pattern of visual loss tell us about the optic nerve lesion?

A

Different parts along the visual pathway give different symptoms - eg if after (behind) optic chiasm will experience symptoms in both eyes.

33
Q

What does the optic nerve do and what does this mean for pathology?

A

Carries sensory fibres from one eye - if pathology here or in retina blurring/symptoms will only affect one eye

34
Q

What does the optic chiasm do? What does this mean for pathology?

A

Mixes sensory fibres from R and L optic nerve - pathology here backwards (to optic tract) can cause visual disturbance in both eyes

35
Q

What does optic tract do?

A

Carries sensory fibres from R and L eye - pathology here will affect both eyes

36
Q

What do cranial nerves III, IV and VI do?

A

Innervate muscles within the orbital cavity responsible for moving the eye - motor

(CN III has additional functions)

37
Q

What is the common route for cranial nerve III, IV and VI?

A

Exit brainstem at different levels then:

Cavernous sinus
Superior orbital fissure
Into orbital cavity

38
Q

What is the clinical test for CN III, IV and VI?

A

Observe resting position of pt’s gaze

Ask patient to perform eye movements - follow finger with eyes

39
Q

What two fibres does the oculomotor CN III carry?

A

Motor and parasympathetic

40
Q

Two fibres for oculomotor

A

Somatic efferent - motor to skeletal

Visceral efferent - parasympathetic

41
Q

What do the somatic efferent fibres of oculomotor suppy?

A

all extraocular muscles except two

muscles in eyelid - levator palpebrae superioris (opens eye)

42
Q

What are extraocular muscles?

A

Muscles that move the eyeball

43
Q

What do the visceral (parasympathetic) efferent fibres supply of oculomotor nerve?

A

Move muscles inside eyeball:
ciliary muscle (thickness of lens)
sphincter papillae (light response)

(parasympathetic non-voluntary)

44
Q

Inspection of oculomotor nerve function CN III

A

Eyelid position - supplies LPS keeps eyelid up

Eye movements - responsible for most muscles and therefore movements

Pupila and pupillary light - supplies muscle controlling pupillary constriction via PS fibres (optic nerve delivers info, oculomotor acts on it)

45
Q

When do signs arise due to a oculomotor lesion? Which fibres are involved?

A

Signs arise due to involvement of lesion of somatic fibres +/- parasympathetic lesion

46
Q

Symptoms of oculomotor lesion

A

Double vision - Dipoplia

47
Q

Signs of oculomotor lesion found on exam

A

Ptosis - eyelid drooping

Abnormal position of eye - down and outwards

Pupil may or may not be dilated (depends if PS fibres involved)

48
Q

Where does oculomotor nerve arise from?

A

Midbrain

49
Q

What does the oculomotor nerve have a close relationship to in its course?

A

Tentorium cerebelli

50
Q

Causes of oculomotor nerve lesions

A

Microvascular ischaemia - blood supply issue

Compressive - lesion compresses onto outside of CN III

51
Q

Risk factors for microvascular ischaemia affecting oculomotor

A

If age >50
Diabetes
Hypertension

52
Q

Examples of compressive oculomotor lesion

A

aneurysm (posterior communicating artery, will also have headache, retro-orbital pain)

head injury

uncul herniation (from raised ICP, nerve has close relationship to tentorium cerebelli)

53
Q

Which oculomotor lesions spare the pupil and which dont?

A

Microvascular ischaemia - spare the pupil

Compressive - pupil involving (more worrying)

parasympathetic fibres of CN nerve III are arranged at periphery of nerve so this is why, PS fibres easily compressed

54
Q

What fibres do the trochlear nerve carry?

A

Motor only

55
Q

What does the trochlear nerve supply?

A

Superior oblique muscle

56
Q

What symptoms will trochlear nerve lesion present with?

A

Double vision - dipoplia

57
Q

What will be found on exam - signs of trochlear lesion

A

Abnormal eye position - subtle

Difficulty moving eye downwards (depression) when eye is inwards (adducted)

58
Q

Where abouts in midbrain does trochlear nerve arise?

A

Dorsal midbrain - none of the others are here

59
Q

Causes of trochlear nerve lesions

A

Congenital or acquired

60
Q

Acquired causes of trochlear nerve lesions

A

microvascular ischaemia (RF >50, diabetes, hypertension)

Trauma (even minor)

Intracranial tumour (can compress/stretch nerve)

61
Q

What fibres does abducens carry?

A

Motor

62
Q

What does abducens supply?

A

Lateral rectus muscle - abducts eyeball

63
Q

What will be symptoms of abducens nerve lesion?

A

Double vision - worse in lateral gaze of vision

64
Q

Examination signs of abducens lesion

A

Abnormal eye position
Difficulty/unable to move affected eye laterally

65
Q

Causes of abducens nerve lesion

A

Microvascular ischaemia
Head injury
Tumour
RAISED INTRACRANIAL PRESSURE OF ANY CAUSE - stretches nerve

66
Q

Where does abducens arise from?

A

Caudal pons

67
Q

Why is the abducens nerve most affected by raise in ICP?

A

Very vertical route between caudal pons (brainstem exit) and cavernous sinus entrance
Fixed at these points
Raised ICP pushes down on nerve displacing it downwards and stretching it

68
Q

What is ‘false’ localising sign?

A

When abducens nerve lesion presents local symptoms due to general raise in ICP as it is stretched

Head and Neck (26 decks)

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