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Head And Neck > Cranial Nerves I-VI > Flashcards

Cranial Nerves I-VI Flashcards

1
Q

Most of the cranial nerves arise from the brainstem.

Are they a part of the CNS or PNS?

A

PNS

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2
Q

How many cranial nerves are;

  • Mixed motor and sensory
  • Purely motor
  • Purely sensory
A

Mixed: 4

Motor: 5

Sensory: 3

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3
Q

What sensory function is carried by the 3 purely sensory cranial nerves?

A

Special sensory function (as opposed to general- temperature, pain etc);

  • Hearing and balance (CN VIII/ Vestibulocochlear)
  • Vision (CN II/ Optic)
  • Smell (CN I/ Olfactory)
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4
Q

How many cranial nerves carry parasympathetic function?

A

Only 4 (3, 7, 9 and 10)

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5
Q

List 3 places where cranial nerves can be damaged due to Injury/ lesion

A
  • During its route outside CNS
  • Brainstem (tumours, other pathology)
  • Tracts within forebrain which communicate with cranial nerves
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6
Q

How are Cranial Nerves I and II atypical?

What is the significance of this?

A
  • They are direct continuations of brain substance therefore can be classified as CNS (other CNs are of PNS)
  • CNS nerves do not regenerate/ repair as easily as PNS therefore injury/ damage can be more significant if in these 2 nerves
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7
Q

How may cranial nerves arise from each section of brain?

Name them all

Remember: 2 2 4 4

A
  • 2 from forebrain (Olfactory, Optic)
  • 2 from midbrain (Oculomotor, Trochlear)
  • 4 from pons (Trigeminal, Abducent, Facial, Vestibulocochlear)
  • 4 from medulla (Glossopharyngeal, Vagus, Accessory, Hypoglossal)
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8
Q

The Olfactory nerve carries Smell and is not routinely tested, rather simply ask patient for any changes in sense of smell/ taste

How do you test it, if you wanted to?

A

Close one nostril and ask to smell something strong (1 nerve for each nostril)

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9
Q

Compare Anosmia and Hyposomia

List 3 causes

(These are associated with Parkinson’s and Alzheimer’s)

A

Anosmia; Absence of sense of smell
Hyposomia; Reduced sense of smell

  • Common cold (most common)
  • Head/ facial injury
  • Anterior cranial fossa tumours
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10
Q

Describe the pathway of the Olfactory nerves from nasal cavity to brain

A
  • Start as nerve fibres in nasal cavity
  • Rise through Cribriform Foramina to form Olfactory Bulbs (1 on each side)
  • Continues as Olfactory tract to Temporal Lobe
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11
Q

How can head/ facial injury cause absent/ reduced sense of smell?

A
  • Very slight posterior displacement of brain

- Shearing of Olfactory nerves as they run through Cribriform Foramina

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12
Q

What are 2 specific things the Optic nerve is responsible for?

What are 3 things that can be used to test the nerve

A
  • Pupillary size
  • Pupil response to light
  • Visual Acuity (Snellen Chart, at opticians)
  • Visual Fields
  • Opthalmoscopy (to directly see nerve)
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13
Q

What are 2 ways patients with optic nerve abnormalities may present

A

Blurred vision/ absence of vision in 1 eye

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14
Q

List 2 diseases that can affect Optic Nerve

A
  • Optic neuritis (inflammation affecting nerve, may be a sign of MS in future)
  • Anterior Ischaemic Optic Neuropathy (Can be caused by Temporal Arteritis)
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15
Q

How can raised intracranial pressure affect Optic nerve

A
  • Increased pressure in Subarachnoid space, which is extended along by optic nerves (they are continuations of forebrain so carry meninges)
  • Nerve compressed from outside-> Impaired flow of substances within axon
  • Impeded blood flow to/ from optic nerves and retina
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16
Q

Describe the pathway of the Optic Nerve fibres

5 steps

A
  • Rods and cones merge into Retinal Ganglion Cells
  • RGC axons form Optic Nerve, with arteries and veins running in the middle
  • Nerve exits orbit through optic canal
  • Fibres from each nerve cross and merge at Optic Chiasm
  • Optic tracts carry mixed information from both eyes towards Primary Visual Cortex (In Occipital lobe)
17
Q

Describe the connection between the Optic Nerve pathway and the Brainstem

A
  • Optic tract allows communication between optic nerve pathway and brainstem
  • This contributes to certain visual reflexes to light (E.g pupil expands/ constricts in response to light)
18
Q

The Oculomotor Nerve (CN III) has both Motor and Parasympathetic targets.

List them

A

Motor;

  • 4 out of 6 extra ocular muscle
  • Levator Palpebrae Superioris
  • Ciliary muscles (ParaS too)

Parasympathetic;
- Sphincter Pupillae muscle (controls pupil size)

19
Q

What are 4 ways we can test the Oculomotor Nerve

A
  • Inspection of resting gaze
  • Eye movements
  • Pupil size and reflexes
  • Eyelid position
20
Q

How do patients with Oculomotor nerve dysfunction typically present?

What do these patients report?

A
  • ‘Down and out’ pointing eyeball
  • Drooping eyelid (Ptosis)
  • Pupil may be dilated (depends on cause)

Report double vision (Dipoplia)

21
Q

Compare 2 types of causes of Oculomotor nerve lesions

A
  1. Microvascular ischaemia;
    - ‘Pupil sparing’ (No dilated pupil)
    - >50, diabetes/ hypertension are risk factors
  2. Compressive;
    - ‘Pupil involving’ (Pupil dilated)
    - Aneurysm of Posterior Communicating Artery compresses nerve (associated with headache/ retro orbital pain)
    - Tentorial herniation (due to raised ICP)
22
Q

Describe the pathway of the Oculomotor nerve in 3 steps

A
  • Leaves midbrain, close to free edge of Tentorium Cerebelli (herniation around here may compress nerve)
  • Passes through Cavernous Sinus (can get a thrombosis here)
  • Passes through Superior Orbital Fissure to enter the orbit, nerve branches into Superior and Inferior divisions (responsible for keeping eyelid open)
23
Q

Why doesn’t Microvascular Ischaemia generally affect the Parasympathetic fibres of CN III

A
  • Motor fibres are affected by ischaemia of central Vasa Nervorum
  • Peripheral parasympathetic fibres have their own vessels, the Pial vessels

(However compression would affect the Parasympathetic fibres first)

26
Q

Is a Pupil Sparing or Pupil Involving CNIII lesion more urgent?

Why?

A

Pupil involving, as the suggests there is something exerting pressure on the nerve (this could be a tumour, haemorrhage, herniation etc.)

27
Q

What is unique about the Trochlear nerve?

This nerve is purely motor, what muscle does it innervate?

A

Comes off Dorsal aspect of brain (midbrain to be exact)

Superior Oblique Muscle of eye

28
Q

What are 2 ways we test the Trochlear nerve?

What are 3 ways patients with lesion of this nerve present

A
  • Inspection of resting gaze
  • Test eye movements
  • Upwards and inwards position of eyeball at rest
  • Double vision (Dipoplia)
  • Head tilt to compensate for abnormal eyeball position
29
Q

Trochlear nerve (CN IV) lesions/ damage can be Congenital or Acquired.

What are 3 ways it can be acquired?

A
  • Microvascular ischaemia (>50, diabetes/ hypertension are risk factors )
  • Trauma (Even minor injury as it is quite thin)
  • Tumour
30
Q

Describe the pathway of the Trochlear nerve

Similar to CN III

A
  • Comes off dorsal aspect of midbrain and wraps around ventrally
  • Passes through cavernous sinus
  • Runs through Superior Orbital Fissure into orbit
  • Goes to supply a single muscle
31
Q

The Abducent/ Abducens nerve is purely motor, but comes off Inferior Pons

What muscle does it innervate?

List 3 ways we can test it

A
  • Inspection of resting gaze
  • Test eye movements
  • Lateral Rectus muscle, which abducts eyeball
32
Q

How do patients with Abducent/ abducens nerve lesions present?

A
  • Double vision (worse in lateral gaze/ when looking laterally)
  • Abnormal eye position
  • Difficultly/ unable to move affected eye laterally
33
Q

The Abducent nerve is the most commonly nerve involved in raised ICP

What are 3 causes of a lesion of this nerve?

A
  • Microvascular ischaemia (>50, diabetes/ hypertension are risk factors)
  • Head injury, tumour
  • Raised ICP-> False localising sign (Symptoms suggest compression when there isn’t any)
34
Q

Describe the pathway of the Abducent nerve

Similar to CN III and IV

A
  • Arises from Pontomedullary junction, travels steeply upwards
  • Passes through cavernous sinus
  • Pass through Superior orbital fissure into orbit to supply muscle
35
Q

Explain how raised ICP can cause a False Localising Sign of the Abducent Nerve

A
  • ICP pushes brainstem downwards, ‘stretching’ Abducent nerve
  • This produces symptoms related to an Abducent nerve lesion
36
Q

List the cranial nerves supplying the eye muscles

Compare their paths

A
  • CN III/ Oculomotor
  • CN IV/ Trochlear
  • CN VI/ Abducent/ Abducens
  • All exit from brainstem
  • All pas through cavernous sinus
  • All enter orbit via Superior Orbital Fissure
37
Q

Outline the structures innervated by the sensory root of the Trigeminal Nerve

A

Face, sinuses, teeth, anterior 2/3 of tongue, scalp

38
Q

How do we test Trigeminal nerve

A
  • Light touch in Va, Vb, Vc dermatomes and ask if patient can feel
  • Test muscles of mastication (chewing, lateral movement)
  • Test Corneal Reflex, which tests Opthalmic branch of Nerve (touch 1 eye’s cornea, makes both eyes blink)
39
Q

List 4 conditions associated with Trigeminal nerve

A
  1. Trigeminal Herpes Zoster;
    - (shingles, reactivation of VZ in Trigeminal ganglion)
    - In a particular dermatome, sight threatening
    - Often Maxillary or Opthalmic (Opthalmic shingles ) dermatomes
  2. Trigeminal Neuralgia;
    - Sharp shooting pains (due to compression from a blood vessel)
  3. Orbital and Mandibular fractures
  4. Posterior cranial fossa tumours
40
Q

Describe the Trigeminal nerve’s exit from the brainstem

Describe briefly the paths of the branches

A
  • Exits at lateral aspect of Pons
  • Continues to Trigeminal ganglion and divides into 3 branches

Opthalmic;

  • Runs through Cavernous Sinus
  • Passes through Superior Orbital Fissure and branches off

Maxillary;

  • Runs through Cavernous Sinus
  • Runs through Foramen Rotundum and branches off

Mandibular;

  • Runs through Foramen Ovale into Infratemporal Fossa
  • Branches off
41
Q

What is Bi-temporal Hemianopia?

How does it present?

A

Optic chiasm lesion

Shit peripheral vision

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