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HNN > Cranial Nerves I-VI > Flashcards

Cranial Nerves I-VI Flashcards

1
Q

What nervous system are cranial nerves part of?
What are the exceptions

A

Peripheral nervous system
Except CNs I + II

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2
Q

Where can injury of a cranial nerve arise?

A
  • route outside the CNS (axon)
  • brainstem (where CN nuclei are located)
  • neurones within brainsteam + forebrain (e.g. upper motor neurones)
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3
Q

Outline cranial nerve topography

A

2,2,4,4
- 2 from forebrain: I, II
- 2 from midbrain: III, IV
- 4 from pons: V, VI, VII, VIII
- 4 from medulla: IX, X, XI, XII

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4
Q

What is CN I?

A

Olfactory nerve
1 nose

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5
Q

Outline the olfactory nerve

A

Cranial nerve I - arises from forebrain
- sense of smell (only sensory)
- test in one nostril at a time

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6
Q

What is anosmia?

A

Absence or reduced sense of smell

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7
Q

Commonest cause of anosmia

A

Common cold/upper respiratory tract infection

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8
Q

Pathway of olfactory nerve I

A
  • olfactory receptors
  • olfactory nerves travels up through holes in ethmoid bone (cribiform foramina)
  • olfactory bulb
  • olfactory tract
  • temporal lobe
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9
Q

How does the olfactory nerve pass through the skull?

A

Cribiform foramina
Through ethmoid bone

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10
Q

What can cause a loss in sense of smell (anosmia)?
Start with most common

A
  • common cold/URTI: most common
  • head/facial injury: shearing olfactory neurones during passage through cribiform foramina
  • anterior cranial fossa tumours: compression of olfactory bulb or tract
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11
Q

What is CN II?

A

Optic nerve

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12
Q

Outline optic nerve

A

Cranial nerve II - arises from forebrain
> carries extensions of meninges
- sense of vision (only sensory)
- pupillary size + response to light

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13
Q

How can you visualise optic nerve II?

A

Ophthalmoscopy

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14
Q

How can you test the function of optic nerve II?

A

Visual acuity (Snellen chart)

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15
Q

Signs + symptoms of optic nerve II lesions

A
  • blurred visions/complete absence of vision
  • poor visual acuity
  • abnormal pupil size + response to light
  • visible pathology on ophthalmoscopy
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16
Q

Pathway of optic nerve II

A
  • retinal ganglion cells axons
  • axons form optic nerve
  • exit via optic canal in sphenoid bone
  • left + right optic nerve merge at optic chiasm
  • continue as right and left optic tracts
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17
Q

How do optic nerves ll travel through the skull?

A

Via optic canal

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18
Q

What is papilloedema?

A

Swollen optic disc

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19
Q

What is cranial nerve lll?

A

Oculomotor nerve

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20
Q

What is cranial nerve lV?

A

Trochlear nerve

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21
Q

What is cranial nerve Vl?

A

Abducens nerve

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22
Q

How many cranial nerves have parasympathetic fibres?
What are they?

A

4
Oculomotor III
Facial VII
Glossopharyngeal IX
Vagus X

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23
Q

How to test the olfactory nerve I?

A
  • change in taste of smell (+ taste associated)
  • one nostril at a time
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24
Q

Which cranial nerves innervate muscles within the orbit (move the eye)?

A

Oculomotor nerve III
Trochlear nerve IV
Abducens nerve VI

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25
Q

Outline the oculomotor nerve

A

Cranial nerve III - arises from midbrain
- somatic efferent fibres: motor innervation to superior, inferior + medial rectus + inferior oblique+ levator palpebrae superioris
- visceral efferent fibres: parasympathetic | sphincter papillae + ciliary body

26
Q

Pathways of the cranial nerves that move the eye
Which are they?

A
  • midbrain: III + IV
  • caudal pons: VI
  • cavernous sinus
  • exits skull through superior orbital fissure into orbital cavity
  • innervates muscles

Oculomotor III, trochlear IV, abducens VI

27
Q

How do you test the Oculomotor nerve III?

A
  • inspect resting gaze
  • eyelid position
  • eye movements H
  • pupillary reflexes
28
Q

Action of levator palpebrae superioris

A

Elevating eyelids (keeps eyelids open)

29
Q

Action of sphincter pupillae

A

Constricts pupil

30
Q

Signs + symptoms of oculomotor nerve III lesions

A
  • ptosis
  • abnormal position of eye down and out
  • possible dilated pupil > if compression on parasympatheic fibres
  • double vision
31
Q

Why do you get ptosis in Oculomotor nerve III lesions?

A

Loss of innervation to levator palpebrae superioris

32
Q

Why can you get a blown pupil in oculomotor nerve III lesions?

A
  • external compression
  • compression of parasympathetic fibres
  • loss of parasympathetic signals to sphincter pupillae muscle
  • oculomotor nerve has a close relationship to tenteorium cerebelli edge v
    uncl herniation - brain herniates over edge of tentorium cerebelli
33
Q

Why do patients present with ‘down and out’ position in oculomotor nerve III lesions?

A
  • Paralysis of 4 extra ocular muscles
  • Only lateral rectus + superior oblique function > ABduction + depression
34
Q

Causes of Oculomotor nerve lesions

A

Pupil sparing:
- microvascular ischaemia

Pupil involving: compressive
- aneurysm
- head injury
- uncul herniation

35
Q

What is ptosis?

A

Dropping eyelid

36
Q

Outline the trochlear nerve

A

Cranial nerve IV - arises from midbrain
- supplies superior oblique muscle

37
Q

Causes of trochlear nerve IV lesions

A

Congential or acquired
- microvascular ischaemia
- trauma: head injury
- intracranial tumour

38
Q

Three risk factors for microvascular ischaemia

A

> 50 years old
Diabetes
Hypertension

39
Q

How do you test the trochlear nerve?

A
  • inspection of resting gaze
  • testing eye movements
40
Q

Signs + symptoms of trochlear nerve IV lesions

A
  • dipoplia: double vision
  • abnormal eye position up and in
  • difficulty moving eye downwards when positioned inwards
41
Q

What is dipoplia?

A

Double vision

42
Q

Action of superior oblique muscle in eye

A

Intorsion
Depression
ABdction

43
Q

What cranial nerve has the longest intracranial length?

A

Trochlear nerve IV

44
Q

Outline the abducens nerve

A

Cranial nerve VI - arises from caudal pons
- supplies lateral rectus muscle in eye
- abducting the eye

45
Q

Signs and symptoms of Abducens nerve VI lesions

A
  • dipoplia - worse in lateral gaze
  • abnormal eye position
  • difficult lateral eye movement
46
Q

What risk relating to raised intracranial pressure does the Abducens nerve VI have due to its pathway?

A
  • arises from caudal pons > vertical route + ‘fixed’ at point of entry into cavernous sinus
  • raised ICP > downwards displacement of brain > stretch abducens nerve route
  • causing false localising sign
47
Q

Which extraoccular muscles does the Oculomotor nerve supply?

A

Superior rectus
Medial Rectus
Inferior rectus
Inferior oblique

48
Q

What is cranial nerve V?

A

Trigeminal nerve

49
Q

Outline the trigeminal nerve

A

Cranial nerve V - arises from the pons
- general sensation to anterior 2/3 tongue
- muscles of mastication via mandibular branch
- sensory function to the face
- three branches from the trigeminal ganglion: ophthalmic, maxillary + mandibular

50
Q

A cranial nerve lesion on the left side will effect what side of the patient?

A

Left side
Cranial nerves from brainstem (after the crossing)

51
Q

What are the branches of the trigeminal nerve V?

A

Opthalamic Va
Maxillary Vb
Mandibular Vc

52
Q

Outline the pathway of the ophthalmic Va branch of the trigeminal nerve
What does it supply?

A
  • pass through cavernous sinus + superior orbital fissure
  • general sensation to forehead, eye + nose
53
Q

How do you test for the trigeminal nerve?

A
  • light touch in Va, Vb, Vc dermatomes
  • test muscles of mastication
  • corneal reflex (ophthalmic division Va test)
54
Q

Sensory supply of the ophthalmic branch Va of the trigeminal nerve

A

sensory: corneal reflex > involuntary blink reflex when cornea is touch

55
Q

Signs and symptoms of trigeminal nerve V lesions

A
  • trigeminal herpes zoster
  • trigeminal neuralgia > causes headaches (shooting pains) due to compression from blood vessel
56
Q

Pathways of the trigeminal nerve V

A
  • ophthalmic: through cavernous sinus + superior orbital fissure
  • maxillary: through cavernous sinus + foramen rotundum
  • mandibular: through foramen ovale
57
Q

What does the ophthalmic nerve Va pass through?

A

Cavernous sinus
Superior orbital fissure

58
Q

What does the maxillary nerve Vb pass through?

A

Cavernous sinus
Foramen rotundum

59
Q

What does the mandibular nerve Vc pass through?

A

Foramen ovale

60
Q

What is Hutchinson’s sign?

A
  • Vesicles involving tip of nose of trigeminal herpes
  • Increased risk of front of eyeball being involved > potential loss of vision
61
Q

What is the afferent and efferent part of the corneal reflex?

A

afferent: trigeminal Va
efferent: facial VII

62
Q

How is the optic nerve affected by increased intra cranial pressure?

A
  • surrounded by extension of the meninges > continuous with the subarachnoid space
  • increased in ICP > increase pressure of CSF > increases tissue pressure within optic nerve
  • axoplasmic flow + venous drainage interrupted

HNN (24 decks)

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