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AHNNA > L15: Cranial nerves 1-6 > Flashcards

L15: Cranial nerves 1-6 Flashcards

1
Q

How many pairs of cranial nerves are there?

A

12 pairs

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2
Q

What is the overall function of cranial nerves?

A

Supplying tissue and structures of the head and neck region including special sense organs
-one exception being the vagus nerve which also has functions outside of the head and neck

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3
Q

What nervous system are the cranial nerves part of?

A

Peripheral NS

-they are associated with the brain stem

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4
Q

Are cranial nerves mixed nerves?

A

Some cranial nerves are mixed, some only carry sensory information, and some only motor information.
-only 4 cranial nerves are parasympathetic

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5
Q

Where can cranial nerves be damaged?

A
  • during its route outside of the CNS
  • the brainstem (where CN nuclei are located) (you would expect to see other signs and symptoms as many other motor/sensory nerves run up and down the brainstem and are tightly packed)
  • tracts within the forebrain which communicate with cranial nerves
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6
Q

Where do the first two cranial nerves emerge from?

A

They are extensions of the forebrain, so aren’t related to the brainstem

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7
Q

Where do the the cranial nerves emerge from?

A

2,2,4,4

  • 2 from the forebrain
  • 2 from the midbrain
  • 4 from the pons
  • 4 from the medulla
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8
Q

What is the function of CN1?

A

Olfactory (special sense smell)

-not routinely tested (but if tested you test one nostril at a time)

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9
Q

How do patients present with damage to CN1?

A

Absence/reduced sense of smell (anosmia/hyposmia)

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10
Q

What are some causes of pathology to CN1?

A

-upper respiratory tract infections (most common)
-head/facial injury
-anterior cranial fossa tumours
(sometimes associated with Parkinson’s/Alzheimer’s)

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11
Q

What is the route of the olfactory nerve?

A
  • arise at the top of the nasal cavity
  • travel through the cribriform foramina (perforations in the cribriform plate of the ethmoid bone)
  • once through the foramina, they are known as the olfactory bulb
  • after the bulb, it is known as the olfactory tract which then enters the temporal lobe
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12
Q

How would you have to have a complete loss of smell?

A

Damage to both olfactory nerves, because they communicate with each other slightly

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13
Q

How do upper resp tract infections cause pathology to CN1?

A

Inside the nasal cavity is lined by respiratory mucosa, and this becomes swollen, interfering the chemicals from reaching the olfactory nerves to trigger an AP

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14
Q

How does impact to the face cause pathology to CN1?

A

There is a perpendicular relation b/w someone punching your face and the nerves coming up from the nasal cavity, and these can therefore get sheared upon impact

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15
Q

What is the overall function of CN2?

A 
Optic nerve (special sense vision)
-carries only sensory info (no pain/temp)
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16
Q

What is the structure of the optic nerve?

A
  • extension of the forebrain

- carries an extension of the meninges

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17
Q

How do you test the optic nerve?

A

Test each one at a time (as they’re a pair)

  • looking at pupil size and response to light
  • test visual acuity (Snellen Chart-found in opticians) and visual fields
  • opthalmoscopy (see optic nerve)
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18
Q

What are the signs and symptoms of damage to the optic nerve?

A

-blurred vision in one eye/complete absence of vision in one eye

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19
Q

What abnormalities would you find upon examination if you have pathology to the optic nerve?

A
  • abnormalities in pupillary function
  • poor visual acuity
  • evidence of pathology involving optic nerve that is visible
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20
Q

Give some examples of disease involving the optic nerve:

A
  • optic neuritis: inflammation of the optic nerve (one of the first signs that appear in someone who will go on to develop MS)
  • AION (anterior ischaemic optic neuropathy): optic nerve looks pale on opthalmoscopy
  • raised intracranial pressure (as it carries the extension of meninges), pressures therefore increase in the subarachnoid space, so nerve is squashed, interfering with movement up and down nerve axons
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21
Q

What part of the optic nerve can you see on an opthalmoscopy at the retina?

A

The optic disc

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22
Q

What is the course of the optic nerve?

A

-originates from cells forming the retina (retinal ganglion cells)
-axons of these cells form the optic nerve
(optic vein and artery are in the middle of the ptic nerve)
-exits the back of the orbit via the optic canal
-fibres from R/L eye merge at the optic chiasm (very close to pituitary gland)
-this then forms the L/R optic tract, where there is communication from optic tract with midbrain to allow for certain visual reflexes

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23
Q

What is the course of the visual pathway?

A

Extends from the retina towards the primary visual cortex found within the occipital lobe
(long pathway)

24
Q

Why does a pituitary tumour affect your sight?

A

They compress the optic chiasm, causing bilateral visual symptoms
-bitemporal hemianopia

25
Q

What is the overall function of CN3?

A

Oculomotor (motor and parasympathetic)

-arises from midbrain

26
Q

What are the target tissues of the oculomotor nerve?

A

Extra ocular muscles (4/6)
Levator palpebrae superioris
Sphincter pupillae muscle

27
Q

How do you test for damage to the oculomotor nerve?

A

-inspect resting gaze
-eye movements, pupillary light reflexes, eyelid position
(pupil may/may not be dilated, it depends on the cause)
Often see an eye with a ‘down and out’ eye with eyelid drooping

28
Q

What are the signs/symptoms of oculomotor nerve damage?

A

Double vision (dipoplia)

29
Q

What are some causes for third nerve lesions?

A

Microvascular ischaemia: >50 yos, diabetes, hypertension (here the pupil is spared)

Compression (pupil involving)

  • CN3 is close to the PCA (posterior communicating artery) which is an artery that develops aneurysms, so the aneurysm can compress the third nerve: associated with headache/retrorbital pain
  • head injury
  • tentorial herniation secondary to increased intracranial pressure (uncus herniates)
30
Q

What is the route of the occulomotor nerve?

A
  • leaves brainstem and approaches the cavernous sinus, here is is very close to the free edge of the tentorium cerebelli
  • runs through cavernous sinus (can get thrombosis here which cause a third nerve lesion)
  • enters the orbit via the superior orbital fissure
  • once inside it branches, gives off superior and inferior division to supply muscles e.g.LPS, and the parasympathetic fibres go on to supply the muscles in the iris
31
Q

What is the function of the levator palpebrae superioris?

A

LPS function is to keep the eyelid up

32
Q

Where do you find the parasympathetic fibres in the occulomotor nerve?

A

Peripherally

33
Q

What is the blood supply to the oculomotor nerve?

A

-vasa nervorum (central in the nerve)
(when you have microvascular disease processes with CN3, it tends to affect the vasa nervorum, so central nerves are more vulnerable, whereas the parasympathetic have a backup blood supply from pia hence why pupil is spared, however in compression the first nerves to be damaged are the parasympathetic so the pupil blows)
-nerves on peripheral aspect, as well as receiving some blood from the vasa nevorum, are in close proximity to pial blood vessels (run in the pia)

34
Q

What is the main function of CN4?

A 
Trochlear nerve (motor only)
-arises from the back of the midbrain
35
Q

What muscle does the trochlear nerve supply?

A

Superior oblique muscle

36
Q

How do you test for damage to the trochlear nerve?

A
  • inspect resting gaze (eye usually takes an upwards and inwards position at rest)
  • test eye movements
37
Q

What signs and symtpoms do you get with trochlear nerve damage?

A
  • dipoplia
  • abnormal eye position (can be subtle)
  • head tilt (to compensate for the abnormal position of the eye)
38
Q

What are some of the causes of trochlear nerve damage?

A 
Acquired:
-microvascular ischaemia 
-trauma (head injury)
-tumour
Congenital
39
Q

What is the route of the trochlear nerve?

A

-comes off the back of the midbrain and comes around to front
-enters the cavernous sinus
-enters orbit via the superior orbital fissure
-supplies the superior oblique muscle)
This nerve is small

40
Q

What is the main function of CN6?

A

Abducens (purely motor)

-comes off the bottom of the pons

41
Q

What muscle does the adbucens nerve supply?

A

Lateral rectus

42
Q

How do you test to see any damage to the abducens nerve?

A
  • inspection of resting gaze

- test eye movements

43
Q

What are the signs/symptoms of damage to abducens nerve?

A
  • dipoplia (this will worsen if the person is gazing laterally)
  • abnormal eye position (more medially)
  • difficulty/unable to move eye laterally
44
Q

What are the causes for abducen nerve damage?

A
  • microvascular ischaemia (diabetes/hypertension)
  • head injury
  • tumours
  • raised intracranial pressure (most commonly damaged nerve by increased ICP): false localising pain- when there isn’t a direct swelling pressing against it, unlike with the uncus herniating onto CN3
45
Q

What is the route of the abducens nerve?

A
  • arises from lower part of pons, at junction called the pontomedullary junction
  • steep upward route to cavernous sinus: this makes it more vulnerable to raised ICP, as things are being pushed downwards and this stretches the nerve
  • enters orbit through superior orbital fissure
46
Q

Which nerve is most likely to be involved in cavernous sinus pathology?

A

Abducens nerve as it passes freely through the centre of the cavernous sinus, whereas the trochlear and oculomotor nerve are at the edge

47
Q

What is the overall function of CN5?

A 
Trigeminal nerve (motor and general sensory)
-branches have an extensive distribution supplying skin of the face and scalp and deep structures of the face
48
Q

Where does the trigeminal nerve originate from?

A

Comes off the side of the pons, halfway down

49
Q

What are the target tissues of the trigeminal nerve?

A
  • skin of face and scalp, and deep structures of the face, anterior 2/3rds of the tongue (sensory)
  • muscles of mastication (motor)
50
Q

How do you test the function of the trigeminal nerve?

A
  • light touch over Va, Vb, Vc dermatomes
  • demonstrate muscles of mastication in action
  • corneal reflex (only tested on high suspicion of trigeminal nerve injury), sensation of touch to the front of the eye is carried by the opthalmic branch of the trigeminal nerve (not the optic nerve)= reflex is blinking, it tests both the motor (reflex) and sensory
51
Q

How will patients present with trigeminal nerve lesions?

A
  • sensory deficits within the dermatomal regions (on affected side)
  • weakness in muscles of mastication (if pathology is involving the mandibular division Vc)
  • absent corneal reflex
52
Q

What are some clinical conditions involving the trigeminal nerve?

A
  • trigeminal herpes zoster (opthalmic division), shingles: reactivationg of VZ (varicella zoster virus) in trigeminal ganglion
  • trigeminal neuralgia (shooting pains in face, due to compression of trigeminal nerve from blood vessel)
  • orbital and mandibular fractures (distal branches affected)
  • posterior cranial fossa tumours
  • brainstem infarcts/lesions
53
Q

What are the 3 branches of the trigeminal nerve?

A

-opthalmic division (V1)
-maxillary division (V2)
-mandibular division (V3)
Nuclei of the trigeminal nerve sits within the pons
Then there is a trigeminal ganglion before it splits into the 3 branches

54
Q

Which branches of the trigeminal nerve pass through the cavernous sinus?

A

Ophthalmic and maxillary

55
Q

Which holes do the branches of the trigeminal nerve run through?

A

Opthalmic: superior orbital fissure (sensory from eye)
Maxillary: foramen rotundum
Mandibular: foramen ovale

AHNNA (25 decks)

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