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Head N Neck > Lecture 6 - Cranial Nerves I-VI > Flashcards

Lecture 6 - Cranial Nerves I-VI Flashcards

1
Q

How many cranial nerves are there??

A

XII (12)

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2
Q

Generally what do the cranial nerves supply?

A

Tissues and structures around th head and neck

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3
Q

How do cranial nerves differ to spinal nerves in terms of types of nerve fibres?

A

Cranial nerves can have different types of fibres (sensory and motor, just sensory, just motor)
Some carry just parasympathetic functions

Spinal nerves are always a mix of sensory and motor

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4
Q

Where abouts can cranial nerves get damaged due to an injury or lesion?

A

Cranial nerve during route outside of CNS

Brainstem (where the cranial nerve nuceli located)

Neurones within forebrain/brainstem which connect to other part of brain to cranial nerve

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5
Q

What is the way to remember where the cranial nerves arise from?

A

Remember 2,2,4,4

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6
Q

Where do the cranial nerves arise from using the 2,2,4,4 topography?

A

2 from forebrain
2 from midbrain
4 pons
4 medulla

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7
Q

What cranial nerves arise from the forebrain?

A

I
II

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8
Q

What cranial nerves arise from the midbrain?

A

III
IV

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9
Q

What cranial nerves arise from the pons?

A

V
VI
VII
VIII

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10
Q

What cranial nerves arise from the medulla?

A

IX
X
XI
XII

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11
Q

What is the name of Cranial nerve I?

A

Olfactory nerve

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12
Q

What function does Cranial nerve I (olfactory nerve) have?

A

Purely sensory
Smell/olfaction

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13
Q

What is the term for absence or reduced sense of smell?

A

Anosmia

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14
Q

What is the most common cause of anosmia/loss of taste?

A

Upper respiratory tract infection

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15
Q

How does an Upper Respiratory Tract Infection lead to anosmia/loss of smell/test?

A

Nasal mucosa swells preventing chemicals from reaching the olfactory nerve

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16
Q

How does the olfactory nerves run through the base of the skull?

A

Runs through the cribriform foramina with the olfactory bulb sitting above

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17
Q

What bone are the cribriform formaina located in which conduct the olfactory nerves?

A

The cribriform plate of the ethmoid bone

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18
Q

What is the route from stimulus to brain for olfaction?

A

Olfactory mucosa (olfactory receptors) -> olfactory nerves -> olfactory bulb -> olfactory tract -> temporal lobe

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19
Q

What are 2 ways by which anosmia can be caused?

A

Head/facial injury (impact)

Anterior cranial fossa tumours

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20
Q

How can a head injury lead to loss of olfaction (anosmia)?

A

Impact can lead to the olfactory nerves shearing as they pass through the cribriform foramina

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21
Q

How can an anterior cranial fossa tumour lead to anosmia?

A

Tumour compresses olfactory bulb or olfactory tract

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22
Q

How can I remember that cranial nerve I is the olfactory nerve?

A

There’s I nose, cranial nerve I

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23
Q

What is the name of Cranial Nerve II?

A

Optic nerve

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24
Q

How can i remember what Cranial nerve II is?

A

Optic nerve for the eyes, 2 eyes CN II

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25
Q

What surrounds the optic nerve (II)?

Therefore what can affect it?

A

3 meningeal layers surround it

Cranial nerve II can therefore be affectd by raised Intracranial pressure

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26
Q

What is the function Cranial nerve II (optic nerve)?

A

Regulates pupil size and response to light

(Sensory part of pupillary light reflex)

27
Q

What is visual acuity?

A

Clarity to how you see

28
Q

With what tool can you directly visualise part of the optic nerve?

A

Ophthalmoscope

29
Q

What measure is used to measure visual acuity?

A

Snellen chart

30
Q

How may someone present who has an optic nerve lesion?

A

Blurred vision or complete abscence of vision in the eye

Poor visual acuity
Abnormalities in pupil size and response to light
Evidence of pathology involving the optic nerve may be visible on ophthalmoscope

31
Q

What forms the optic nerve?

A

All the retinal ganglion cells axons joining together

32
Q

What is the route of the optic nerve?

A

Exits back of orbit via the optic canal

33
Q

What is the name of the structure at which the left and right fibres of the optic nerve merge?

A

Optic chiasm

34
Q

What happens once the optic nerves merge at the optic chiasm?

A

Continue as left and right optic tracts continuing to visual pathway or communicating from tract into brainstem

35
Q

What structure is the optic chiasm close to?

A

Pituitary gland

36
Q

What is the clinical relevance of the pituitary being near the optic chiasm?

A

Pituitary tumour can compress the optic chiasm

37
Q

What can lead to an Optic nerve leasion (II)?

A

Any disease involving optic nerve:
-optic neuritis
-anterior ischaemic optic neuropathy

38
Q

How can you tell someone has an optic nerve (II) lesion?

A

Use ophthalmoscope tot see of they have a swollen optic disc (papilloedema)

39
Q

What leads to papilloedema?

A

Swollen optic disc happens due to a raised Intracranial Pressure

40
Q

What part of the brain does the optic tracts communicate with for the visual pathway?

A

Optic tracts communicate with midbrain of brainstem

41
Q

What is the general function of the cranial nerve III, IV and VI?

A

Innervates the muscles within the orbit (extra-occupation muscles) to move the eye

42
Q

What is Cranial nerve III?

A

Oculomotor nerve

43
Q

What is cranial nerve IV?

A

Trochlear nerve

44
Q

What is cranial nerve VI?

A

Abducens nerve

45
Q

What is the route for the cranial nerve supplying the extra-ocular muscles moving the eye?
III =Oculomotor
IV = Trochlea
VI = Abducens

A

Travel through cavernous sinus through superior orbital fissure to the orbital cavity

46
Q

What is the motor function of the Oculomotor nerve (III)?

A

Innervates 4 out of 6 extra ocular muscles

Muscle in eyelid = levator Palpebrae superioris (skeletal muscle part)

47
Q

What is the parasympathetic function of the Oculomotor nerve (III)?

A

Innervates sphincter papillae (contracts size of pupil)

Innervates ciliary body (controlling size of lens)

48
Q

What is the function of levator palpebrae superioris?

A

Keeps eyelids retracted

49
Q

What dural fold does tthe Oculomotor nerve (III) run close to?

A

Tentorium cerebelli

50
Q

Why in an uncal herniation can you see a blown pupil with an ophthalmoscope?

A

The parasympathetic fibres of the Oculomotor nerve are superficial

51
Q

How can people with Oculomotor nerve lesions present?

A

Dipoplia (double vision)

Ptosis (droopy eyelid)

Abnormal position (Down and out)

Pupil may be dilated

52
Q

What are some pupil sparing causes of Oculomotor nerve lesions?

A

Micro vascular ischameia (diabetes/hypertension)

53
Q

What are some pulp involving causes of Oculomotor nerve lesions?

A

Compressive:
-aneurysmal
-head injury
-uncal herniation secondary to increased intracranial pressure

54
Q

What is the function of the Trochlear nerve (Cranial nerve IV)?

A

Supplies Superior oblique muscle

55
Q

How do people present with CN IV/Trochlear nerve lesions?

A

Dipoplia

Abnormal eye position
Difficult moving eye down when the eye is positioned inwards

56
Q

What part of the midbrain does the Trochlear nerve (CN IV) arise from?

A

Dorsal part

57
Q

What can cause Trochlear nerve lesions?

A

Congenital

Microvascular ischameia (diabetes/hypertension)
Trauma
Intracranial tumour (May stretch or impress CN IV)

58
Q

What is the function of Cranial nerve VI (Abducens)?

A

Supplies 1 muscle

59
Q

How does someone present with CN VI Abducens nerve lesion?

A

Dipoplia worse in lateral gaze on side of lesion

Eye sits medially when asked to look straight at rest

60
Q

What part of the brainstem does the Abducens nerve (VI) aris from?

A

Caudal pons

61
Q

How does the Abducens nerve run?

A

From back of pons and climbs very steeply vertically to enter cavernous sinus

62
Q

Why is the Abducens nerve (VI) the most vulnerable to being stretch and damaged out of III, IV and VI?

A

The steep upwards climb makes it vulnerable to being stretch as it travels to the cavernous sinus

63
Q

What can lead to Abducens nerve (VI) lesions?

A

Microvascular ischaemia
Head injury, tumour

Raised Intracranial pressure

Head N Neck (24 decks)

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