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Cranial Nerves > Cranial Nerves > Flashcards

Cranial Nerves Flashcards

1
Q

How many pairs of cranial nerves are there?

A

12

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2
Q

What are the cranial nerves, in order?

A

(1) Olfactory, (2) Optic, (3) Oculomotor, (4), Trochlear, (5) Trigeminal, (6) Abducens, (7) Facial, (8) Vestibulocochlear, (9) Glossopharyngeal, (10) Vagus, (11) Accessory Spinal, (12) Hypoglossal.

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3
Q

What are the 3 different functions of cranial nerves?

A

(1) Motor to voluntary muscles.
(2) Motor to involuntary muscles.
(3) Sensory.

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4
Q

What is the function of the olfactory nerve (CN1)?

A

It is a special sensory nerve that provides the sensation of smell.

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5
Q

Where is the olfactory nerve?

A

It is present in the olfactory epithelium at the top and back of the nose.

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6
Q

What is the structure of the olfactory neurones?

A

The neurones are bipolar (they have 2 extensions) and are specific for special senses. They have non-motile cilia which extend out into the air space and interact with odourants.

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7
Q

How does the olfactory system work?

A

Afferent nerve fibres of the olfactory nerve send impulses to about external odours to the CNS where they are perceived.

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8
Q

What is the condition associated with the damage of the olfactory nerve?

A

Anosmia.

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9
Q

How do we recover from anosmia?

A

The olfactory nerve has basal cells which are basically stem cells of the olfactory neurones. The divide and then differentiate into sensory nerve cells (bipolar). This axon reconnects with the olfactory bulb where they finally differentiates into olfactory neurones.

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10
Q

What is the function of the optic nerve (CN2)?

A

CN2 is a special sensory nerve allowing vision.

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11
Q

How does the optic nerve work?

A

Light enters the eye via the pupil where it is received by the retina. The retina has rods (responsible for monochrome vision) and cones (responsible for colour vision). These then depolarise the optic nerve which travels through the orbital canal to the occipital lobe where the vision centre is present.

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12
Q

What are the general functions of the oculomotor nerve (CN3)?

A

It has somatic motor and visceral motor functions.

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13
Q

What somatic motor movements does CN3 do?

A

CN3 innervates muscles to move the eye.

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14
Q

What somatic muscles does the oculomotor nerve innervate?

A

Superior rectus muscle: moves eye upwards.
Medial rectus muscle: moves eye inwards towards the nose.
Inferior oblique muscle: moves eye upwards and outwards.
Levator Palpebrae Superioris: holds eyelid open.

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15
Q

What visceral muscles does the oculomotor nerve innervate?

A

Parasympathetic innervation of:

Sphincter Pupillae: contraction leads to the constriction of the pupil.

Ciliary Muscle: changes the shape of the lens to allow the eye to accommodate viewing objects at varying distances.

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16
Q

Where does the optic nerve originate?

A

In the midbrain.

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17
Q

What happens when intracranial pressure increases?

A

Increased ICP causes compression of the CN3. This destroys the function of the sphincter pupillae so the pupils dilate, 4 somatic muscles are also damaged so the individuals will struggle to move the eye upwards, outwards or inwards and the eyelid will sag.

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18
Q

What is the trochlear nerve function (CN4)?

A

Somatic motor nerve that moves the eye downwards and outwards.

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19
Q

What muscle does the trochlear nerve damage?

A

It innervates the superior oblique muscle to move the eye downwards and outwards.

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20
Q

What is caused by damage to CN4?

A

CN4 is rarely damaged on its own. If it is, diplopia occurs. The patient will experience double vision when they look down.

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21
Q

What is the function of the trigeminal nerve (CN5)?

A

This is a general sensory nerve.

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22
Q

What is the structure of the trigeminal nerve?

A

There are 3 branches:

Ophthalmic Branch
Maxillary Branch
Mandibular Branch.

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23
Q

What is the function of the ophthalmic branch?

A

Provides sensation from the cornea, skin of the forehead, scalp, eyelids, nose, mucosa of the nasal cavities (top of the nose) and the paranasal sinuses.

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24
Q

What is the function of the maxillary branch?

A

Provides sensation to the upper jaw bone, lower part of the nose and eye socket, the upper lip, maxillary teeth and maxillary sinuses.

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25
Q

What is the function of the mandibular branch?

A

provides sensation of the lower jaw, mandibular teeth, mucosa of the mouth and anterior 2/3rds of the tongue.

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26
Q

What is the name and function of the mandibular extension branch?

A

Inferior alveolar nerve. Supplies sensation to the lower teeth.

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27
Q

What is the name and function of the maxillary extension branch?

A

Superior alveolar nerve. Supplies sensation to the upper teeth.

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28
Q

What are the motor functions produced by the trigeminal nerve?

A

Trigeminal nerve allows biting and chewing.

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29
Q

What motor muscles did the trigeminal nerve innervate to allow mastication?

A

Temporalis
Masseter
Lateral Pterygoid
Medial Pterygoid

30
Q

What is the function of the anterior part of the temporalis?

A

Responsible for closing the lower jaw.

31
Q

What is the function of the posterior part of the temporalis?

A

Responsible for holding the lower jaw in place.

32
Q

What is the function of the massetter?

A

Responsible for closing the lower jaw.

33
Q

What is the function of the lateral pterygoid?

A

Responsible for opening the lower jaw.

34
Q

What is the function of the medial pterygoid?

A

Responsible for closing the lower jaw, protrudes the lower jaw and helps the chewing action.

35
Q

What is the function of the abducens nerve (CN6)?

A

Somatic motor nerve.

36
Q

What muscle does the abducens nerve innervate?

A

It innervates the lateral rectus. This allows the left eye to move left or the right eye to move right. This doesn’t occur at the same time.

37
Q

Where does the abducens nerve arise from?

A

Arises from the pons.

38
Q

What is the function of the facial nerve (CN7)?

A

Branchial motor nerve and visceral motor nerves. It also has special sensory neurones.

39
Q

What is the branchial motor function?

A

The branchial motor innervates all 43 muscles in the face, allowing facial expression

40
Q

Why is there an odd number of facial nerves?

A

There are 21 pairs of facial nerves that control facial expression across the face. The 43rd muscle is a singular muscle that allows movement of the lips.

41
Q

What is the stapedius muscle?

A

The stapedius muscle is in the ear. When there is a loud noise, this muscle contracts to reduce vibrations to reduce damage in the ear.

42
Q

What is the special sensory function of CN7?

A

CN7 provides taste sensation from the front 2/3rds of the tongue.

43
Q

What are the visceral motor functions of CN7?

A

Provides parasympathetic innervation of the submandibular glands (major salivary glands located in the floor of the mouth) and sublingual glands (smaller salivary glands). Saliva is required for lubrication of the mouth and throat as well as beginning digestion.

44
Q

What is the function of the vestibulocochlear nerve (CN8)?

A

This is a special sensory nerve carrying information to the CNS from the ear about hearing and balance.

45
Q

What are the 2 branches of CN8?

A

Cochlear Nerve

Vestibular Nerve

46
Q

What is the function of the cochlear nerve?

A

Carries information about hearing from the ear to the CNS.

47
Q

What is the function of the vestibular nerve?

A

Carries information about balance from the inner ear to the CNS.

48
Q

Where does the sensation of dizziness come from?

A

The inner ear contains semi-circular ducts that have liquid in them. When we move, this liquid moves as well and provides balance information. However, constant spinning leads to the liquid spinning more slowly than the physical action of spinning. This leaves the information miss-leading to the brain and that is where the dizzy sensation comes from.

49
Q

What is Vestibular Schwannoma?

A

A small tumour forms in the region where the vestibular nerve originates. It forms from the myelin forming cells of the CNS. CN8 is compressed so balance and hearing is impacted. CN 7 is also effected and causes facial muscle weakness.

50
Q

What are the 5 functions of the glossopharyngeal nerve (CN9)?

A

(1) Somatic Motor
(2) Visceral Motor
(3) Visceral Sensory
(4) Special Sensory
(5) Somatic Sensory

51
Q

What muscle is innervated for somatic motor movement and what does it do?

A

Innervation of the stylopharyngeus muscle elevates the larynx and the pharynx. It dates the pharynx to allow the passing of food.

52
Q

What do the visceral motor fibres innervate and what does this do?

A

The visceral fibres innervate parasympathetic neurones to the parotid gland. These are large salivary glands situated on either side of the mouth. They secrete serous saliva to facilitate mastication and swallowing.

53
Q

What do the visceral sensory fibres do?

A

They are present in the carotid sinus and carotid body of the carotid artery that runs down either side of the throat.

54
Q

What do the special sensory fibres do?

A

Carries sensory information from the posterior 1/3rd of the tongue.

55
Q

What do somatic sensory fibres do?

A

Carries sensory information from the external ear.

56
Q

What are the 3 functions of the Vagus Nerve (CN10)?

A

(1) Visceral Sensory
(2) Special Sensory
(3) General Sensory

57
Q

What are the visceral sensory functions?

A

Provides sensory information from the tongue, larynx, respiratory tract, heart and upper GI.

58
Q

What are the special sensory functions?

A

Provides sensory information from the epiglottis and the whole palate.

59
Q

What are the general sensory functions?

A

Provides sensory information from the auricle (external air) and the external auditory meatus (a tube running from outer ear to inner ear).

60
Q

What is the function of the spinal accessory nerve (CN11)?

A

It has a somatic motor function only.

61
Q

What does CN11 innervate?

A

The CN11 innervates the sternocleidomastoid muscle and the trapezius muscle.

62
Q

What is the function of the sternocleidomastoid muscle?

A

When innervate, it is responsible for the rotation of the head and flexion of the neck.

63
Q

What is the function of the trapezius muscle?

A

Responsible for moving, rotating and stabilising the shoulder blade. It is also responsible for extending the head and neck.

64
Q

What is the function of the hypoglossal nerve (CN12)?

A

It has a somatic motor function only.

65
Q

What muscles does the hypoglossal nerve innervate and for what function?

A

It innervates the intrinsic and extrinsic muscles of the tongue to allow tongue manipulation.

66
Q

What does bilateral innervation mean?

A

Both nerves in a pair are innervated by both the left and right hemisphere of the brain.

67
Q

What does contralateral innervation mean?

A

The left nerve of a pair is innervated by the right hemisphere and vice versa.

68
Q

What nerves are innervated bilaterally?

A

All the cranial nerves with the exception of the facial nerve (CN7) and the hypoglossal nerve (12).

69
Q

What nerves are innervated contra laterally?

A

All of the corticospinal nerves are innervated contra laterally.

70
Q

Why is bilateral innervation a safety mechanism?

A

If a unilateral lesion develops on 1 nerve of a pair, the muscles innervated by this nerve will NOT be paralysed. Instead, both the left and right nerve will still receive electrical impulses. However, the motor movement will be weaker.

71
Q

What causes Bell’s Palsy?

A

Because CN7 and CN12 are innervated contra laterally, a unilateral lesion would causes paralysis of 1 of the nerves in the pair. If the lesion is on the left hand nerve, the muscles in the lower face will weaken and so the face will droop.

Cranial Nerves (1 decks)

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