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Head and Neck > Lec 7 - Cranial nerves I - VI > Flashcards

Lec 7 - Cranial nerves I - VI Flashcards

1
Q

What do the cranial nerves in general supply?

A

They supply structures of the head and neck.

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2
Q

What kind of axons do the cranial nerves carry?

A
  1. purely special sensory –> these include the special senses such as taste and smell.
  2. purely motor
  3. mixed: sensory and motor.
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3
Q

What does the brainstem do?

A
  1. adjoins the brain to the spinal cord , some it is continuous with the spinal cord caudally.
  2. The brainstem plays a vital role in the regulation of the cardio-respiratory functions (regulates HR and breathing) and the maintaining of consciousness.
  3. Ascending sensory and descending motor fibres between the brain and the rest of the body run through the brainstem.
  4. The brainstem is the location of the majority of cranial nerve nuclei.
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4
Q

What are the parts of the brainstem?

A
  1. Brain (forebrain)
  2. midbrain
  3. pons
  4. medulla
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5
Q

How many cranial nerves are in each section of the midbrain?

A
  1. Brain (forebrain) —> 2 CNs —> These are actually extensions of the forebrain.
  2. Midbrain —> 2 CNs
  3. Pons —> 4 CNs
  4. Medulla —> 4 CNs
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6
Q

What is CN I?

A

The olfactory nerve.

- It is paired anterior extensions of forebrain rather than a true cranial nerve.

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7
Q

Describe the pathway of the Olfactory nerve (CN I)?

A
  1. olfactory nerves start at the roof of the nasal cavity.
  2. Then go to the cribriform foramina.
  3. Then to the olfactory bulb, which is where all the cell bodies of the olfactory nerves are.
  4. Then goes to the olfactory tract.
  5. Then goes to the temporal lobe which is used in the perception of smell.
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8
Q

What type of nerve is the olfactory nerve and what is its function?

A
  • It is special sensory.

- Function is olfaction –> sense of smell.

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9
Q

What can happen due to damage/ lack of function of CN I olfactory nerve?

A
  1. Anosmia

2. Tumours at the base of the frontal lobes within the anterior cranial fossa may involve CN I.

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10
Q

What is the CN I olfactory nerve associated with?

A

The anterior cranial fossa.

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11
Q

What is anosmia?

A
  • Anosmia is the loss of sense of smell.
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12
Q

What are causes of anosmia?

A
  • common cold is the most common cause.

- Head injury secondary to shearing forces and/ or basilar skull fracture can also cause anosmia.

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13
Q

What is CN II?

A

The optic nerve

- It is paired anterior extensions of forebrain rather than a true cranial nerve.

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14
Q

What pathway is the optic nerve part of and how is this achieved?

A
  • The visual pathway.
  • takes signal from retina back to the occipital node allowing the signal to be perceived as vision.
  • impulses are generated by cells within the retina in response to light, generates action potentials which propagate along the optic nerve.
  • –>Via other components of the visual pathway they reach the primary visual cortex where they are perceived as vision.
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15
Q

Describe the pathway of the CN II optic nerve?

A
  1. Axons from the retinal ganglion cells form the optic nerve.
  2. It then exits back of the orbit via the optic canal.
  3. The fibres then cross and merge at the optic chiasm.
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16
Q

What does the optic nerve do?

A

The optic nerve carries sensory fibres from the one eye (retina)

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17
Q

What does the optic chiasm do?

A

The optic chiasm does the mixing of sensory fibres from right and left optic nerves.

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18
Q

What does the optic tract do?

A

The optic tract contains sensory information from part of the right eye and part of the left eye.

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19
Q

What do different lesions within the visual pathway do?

A

They give very different patterns of visual loss, which may include:

  • retinal detachment
  • optic neuritis
  • pituitary tumour
  • stroke
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20
Q

What can pituitary tumours do in relation to vision?

A
  • Pituitary tumours compress the optic chiasm causing bilateral visual symptoms which are known as BITEMPORAL HEMIANOPIA.
  • —> This is when you lose the lateral parts of the field of vision.
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21
Q

how do you test the function of the optic nerve?

A

By visual acuity tests such as:

  • snellen chart
  • checking visual fields
  • testing pupillary responses.
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22
Q

What is the optic disc?

A

It is the point at which the nerve enters the retina.

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23
Q

How can you see the optic nerve?

A

Through an ophthalmoscope.

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24
Q

When may the Optic nerve swell?

A
  • As the optic nerve carries the extension of meninges so the nerve can swell due to raised intracranial pressure .
  • –> The optic disc may appear as swollen due to the raised intracranial pressure, which is known as papillodema.
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25
Q

What is CN III?

A

The oculomotor nerve.

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26
Q

Describe the pathway of the oculomotor nerve CN III?

A
  1. Midbrain
  2. Then runs through the lateral wall of the cavernous sinus.
  3. Then foes to the superior orbital fissure
  4. then to the orbit
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27
Q

What type of nerve is the oculomotor nerve?

A

It is motor and autonomic.

- it also carries autonomic parasympathetic fibres.

28
Q

What are the functions of the oculomotor nerve and state whether they are voluntary or autonomic?

A
  1. Innervates most of the muscles that move the eyeball ( done by extra-ocular muscles) —> voluntary control.
  2. Innervates the muscle of the eye lid (LPS) —> voluntary control
  3. Innervates the sphincter pupillae muscle (which constricts the pupil) —> Autonomic
  4. Cilliary muscle, which surrounds where the lens is in your eye and is used to focus on near and far objects —> autonomic.
29
Q

What is the oculomotor nerve vulnerable to?

A

It is vulnerable to compression between the tentorium cerebelli and part of the temporal lobe when intracranial pressure is raised.
- you may also get a blown pupil if the innervation by the oculomotor nerve is lost causing the pupil to stay dilated.

30
Q

How do you test the function of the CN III oculomotor nerve?

A
  1. By inspecting the eyelids and pupil size
  2. By testing eye movements
  3. By testing the pupillary reflexes for example to light.
31
Q

What can the pathology of the oculomotor nerve cause?

A
  • It can cause pupillary dilation and/ or double vision (diplopia)
  • There is also a down and out position with severe ptosis which is when the eyelid droops.
32
Q

What are the causes for injury/ pathology of the oculomotor nerve?

A
  1. Raised Intracranial pressure caused by a tumour or haemorrhage —> causes external compression of the oculomotor nerve.
  2. Aneurysms —> causes external compression of the oculomotor nerve.
  3. Cavernous sinus thrombosis —> causes external compression of the oculomotor nerve.
  4. Vascular causes which are secondary to diabetes/ hypertension. —> These are typically due to pupil sparing.
33
Q

What is the CN IV?

A

The Trochlear nerve.

  • It is unusual as it is the only cranial nerve to come from the back of the midbrain.
  • –> In other words it is the only nerve to emerge from the dorsal aspect go the brainstem.
  • CN IV has the longest intracranial course of any of the cranial nerves.
34
Q

Describe the pathway of the Trochlear nerve CN IV.

A
  1. Midbrain
  2. goes to the cavernous sinus
  3. goes to the superior orbital fissure.
35
Q

What type of nerve is the trochlear nerve CN IV?

A

it is purely motor.

36
Q

What is the function of the trochlear nerve?

A

It innervates one of the muscles that move the eyeball, which is the superior oblique —> this is an extra-ocular muscle.

37
Q

How do you test the function of the trochlear nerve?

A

By testing eye movements

—>Cranial nerves III, IV and VI are all tested at the same time.

38
Q

What can happen due to damage to the trochlear nerve?

A
  1. Diplopia (double vision)
    - -> this is worse on downward gaze for example when reading or walking downstairs.
    - -> Diplopia is rare and often subtle as it can be corrected with the tilt of the head.
  2. Congenital palsies in children which has uncertain causes.
39
Q

What is most common cause of acute CN IV injury and any cause of raised ICP?

A

Head injury

40
Q

What are the four cranial nerves within the pons?

A
  1. trigeminal (V)
  2. abducens (VI)
  3. Facial (VII)
  4. Vestibulocochlear (VIII)
41
Q

What is CN V?

A

Trigeminal nerve

42
Q

What does the trigeminal nerve supply?

A

The trigeminal nerve has branches which have an extensive distribution that supplies the skin of the face and scalp as well as deep structures of the face.

43
Q

Describe the

pathways of the Trigeminal nerve branch Va.

A
  1. Pons
  2. Trigeminal ganglion
  3. Va
  4. passes through the wall of the cavernous sinus
  5. Then to the superior orbital fissure
  6. ends at orbit.
44
Q

Describe the

pathways of the Trigeminal nerve branch Vb.

A
  1. Pons
  2. Trigeminal ganglion
  3. Vb
  4. passes through the wall of the cavernous sinus
  5. Then to the foramen rotundum
  6. ends at the pterygopalantine fossa
45
Q

Describe the

pathways of the Trigeminal nerve branch Vc.

A
  1. Pons
  2. Trigeminal ganglion
  3. Vc
  4. passes to the foramen ovale
  5. ends at the Infratemporal fossa.
46
Q

What type of nerve is the trigeminal nerve?

A

It is general sensory and motor (only Vc has motor fibres)

47
Q

What are the general sensory functions of the trigeminal nerve?

A
  1. The trigeminal nerve is the main sensory nerve that supplies skin of the face and part of the scalp.
  2. it is sensory to deeper structures within the head such as paranasal air sinuses, nasal and oral cavity, anterior part of tongue (excludes taste) and meninges.
48
Q

What is the motor function of the trigeminal nerve?

A

It is motor to muscles of mastication in Vc only.

49
Q

How do you test the function of the trigeminal nerve?

A
  1. Test by checking sensation in areas of its dermatomes (Va, Vb, Vc)
  2. By testing muscles of mastication —> jaw jerk
  3. by testing corneal reflex.
50
Q

What are some conditions that involve branches of the trigeminal nerve?

A
  • trigeminal neuralgia

- shingles - e.g ophthalmic shingles can be sight threatening and affect vision.

51
Q

How do you test the function if the maxillary branch of the trigeminal nerve?

A
  • test sensation underneath the eye.
52
Q

What are the two nerves within the maxillary division of the trigeminal nerve?

A
  • Infraorbital nerve

- Superior alveolar nerve

53
Q

What does the infraorbital nerve do?

A
  • It runs through the floor of the orbit.
  • it carries sensory from area of the cheek and lower eye lid.
  • it is susceptible to injury in orbital floor fractures.
54
Q

What does the superior alveolar nerve do?

A
  • It carries sensory from upper teeth and hums

- this nerve may be blocked by dentists.

55
Q

What are the nerves within the mandibular division of the trigeminal nerve?

A
  • Inferior alveolar nerve
  • Lingual nerve
  • Auriculotemporal nerve
56
Q

What do the supraorbital and supratrochlear nerves do?

A
  1. sensory from the forehead/ anterior scalp.

2. they follow the blood vessels of the same name.

57
Q

What does the inferior alveolar nerve do?

A
  • It runs through the bony canal in the mandible, existing as a mental nerve. –> passes via the mental foramen.
  • It carries sensory from area of area mental protuberance (chin), lower lip and gum.
  • It is susceptible to injury in mandibular fractures.
58
Q

What does the lingual nerve do?

A
  • It carries general sensory from the anterior part of the tongue.
59
Q

What does the auriculotemporal nerve do?

A
  • It carries general sensory from part of the ear, temple area/ lateral side of head and scalp and TMJ.
60
Q

What is CN VI?

A

The Abducens nerve.

61
Q

Describe the pathway of the abducens nerve?

A
  1. Comes from the Lower puns (junction between pons and medulla)
  2. It runs upwards before being able to pass into the cavernous sinus.
  3. It then enters into the orbit via the superior orbital tissue.
62
Q

What type of nerve is the abducens nerve CN VI?

A

it is purely motor.

63
Q

What is the function of the abducens nerve?

A

It innervates one muscle that moves the eye

—> This is done by an extra ocular muscle called the lateral rectus.

64
Q

When can the abducens nerve be easily stretched?

A
  • It can be easily stretched in raised ICP.
  • –> This is due to emerging anteriorly at the point-medullary junction before running under the surface of the pons upwards towards the cavernous sinus.
65
Q

How do you test for the function of the abducens nerve?

A
  • test by doing eye movements which at the same time tests the cranial nerves III, IV and VI.
66
Q

What do patients with damage to abducens nerve present with and what are they susceptible to?

A
  • present with diplopia

- susceptible to injury in raised ICP due to bleed or tumour etc.

Head and Neck (8 decks)

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