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Flashcards in Cranial nerves Deck (53)
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1

Name and describe the course of CNI

The Olfactory Nerve

Stemming from the left and right olfactory bulbs, exits the Skull through the cribriform plate and terminating in the roof of the nasal cavity, this nerve governs the olfactory nerve fibers which register smell.

2

Name and describe the course of CN II

The Optic Nerve Stemming on the left and right side from the optic chiasm, exiting the skull through the optic canal and terminating in the eye, this nerve governs the ocular and sensory functions.

3

Name and course of CNIII

The Oculomotor Nerve

 

Stemming from the mesial superior margin of the left and right side of the pons, exiting the skull through the superior orbital fissure and terminating in the muscles of the eye: ciliary, sphincter pupillae and all the external eye muscles except: superior oblique and lateral rectus.

 

This nerve motorically innervates the previously mentioned eye muscles and allows the eye to move within the orbit

4

Name and course of CN IV

The Trochlear Nerve

Stems from the lateral superior margin of the left and right side of the pons, exiting the skull through the superior orbital fissure and terminating in the superior oblique eye muscle

Motorically governs the abduction, depression and internal rotation of the eye.

5

Name and course of CN V

The Trigeminal Nerve

 

Stems from the lateral superior margin of the left and right side of the pons, this nerve branches into three: V/I ophthalmic, V/II maxillary and V/III mandibular nerves. These branches exit the skull through the superior orbital fissure (V/I), the foramen rotundum (V/II) and the foramen ovale (V/III).

 

This nerve governs the sensory innervation of the face, sinuses and teeth.

6

Name and course of CN VI

The Abducent Nerve

Stems from the medial inferior margin of the left and right side of the pons and the left and right pyramids, this nerve exits the skull via the superior orbital fissure and innervates the lateral rectus muscle of the eye, which retracts the eye within the orbit.

7

How many cranial nerves are there? State whether they are part of the CNS of PNS.

12 Pairs

PNS

8

Name and course of CN VII

The Facial Nerve

 

Stems from the lateral inferior margin of the left and right side of the pons and the left and right olives, this nerve exits the skull through the Internal acoustic meatus.

It supplies the muscles of the face with motoric fibers and taste sensation to the anterior two thirds of the tongue.

9

Name and course of CN VIII

 The Vestibulocochlear Nerve

Stemming from the lateral inferior margin of the left and right side of the pons and the cerebellum, exiting the skull via the internal acoustic meatus, this single nerve contains both vestibular and cochlear fibers. The cochlear fibers terminate in the cochlea and the vestibular fibers terminate in the ampullae of the vestibulum.

 

They supply sensory innervation to the inner ear.

10

Name and course of CN IX

The Glossopharyngeal Nerve

Stemming from between the olives and the cerebellum, this nerve exits the skull via the jugular foramen.

 

11

Name and course of CN X

The Vagus Nerve

Stemming from between the olives and the cerebellum, this nerve exits the skull via the jugular foramen.

It motorically innervates the heart, lungs, palate, pharynx, larynx, trachea, bronchi and gastrointestinal tract. It provides sensation to the heart, lungs, trachea, bronchi, larynx, pharynx, gastrointestinal tract and the external ear.

12

Name and course of CN XI

 The Accessory Nerve

Stemming from between the cuneate fasciculus and lateral funiculus and exiting the skull via the jugular foramen, this nerve motorically innervates the Sternocleidomastoid muscles and Trapezius muscles.

13

Name and course of CN XII

The Hypoglossal Nerve

Stemming from between the gracile and cuneate fasciculus, this nerve exits the skull via the hypoglossal canal. It motorically innervates the muscles of the tongue, except the palatoglossus, which is innervated by the vagus nerve (CN X). It also gives C1-3 fibers to the strap muscles (infrahyoid muscles).

14

How is the optic nerve different from the other cranial nerves?

The optic nerve is surrounded by cranial meninges (not by epi-, peri- and endoneurium like most other nerves).

15

Describe the contents of the left and right optic tracts.

Left optic tract – contains fibres from the left temporal (lateral) retina, and the right nasal (medial) retina.

Right optic tract – contains fibres from the right temporal retina, and the left nasal retina.

16

Describe the effect of a pituitary tumour pressing on the optic chiasm

This produces visual defect affecting the peripheral vision in both eyes, known as a bitemporal hemianopia

17

Describe the cell types found within the olfactory mucosa

Basal cells: Form the new stem cells from which the new olfactory cells can develop.

Sustentacular cells: Tall cells for structural support. These are analogous to the glial cells located in the CNS.

Olfactory receptor cells: bipolar neurons which have two processes, a dendritic process and a central process. The dendritic process projects to the surface of the epithelium, where they project a number of short cilia, the olfactory hairs, into the mucous membrane. These cilia react to odors in the air and stimulate the olfactory cells. The central process (also known as the axon) projects in the opposite direction through the basement membrane.

In addition to the epithelium, there are Bowman’s glands present in the mucosa, which secrete mucus.

18

Where does the olfactory bulb lie?

Olfactory groove

19

What does the  superior branch of the occulomotor nerve innervate and what are its actions?

Superior rectus – Elevates the eyeball

Levator palpabrae superioris – Raises the upper eyelid.

20

What does the inferior branch of the occulomotor nerve innervate?

Inferior rectus – Depresses the eyeball

Medial rectus – Adducts the eyeball

Inferior oblique – Elevates, abducts and laterally rotates the eyeball

21

What two structures of the eye recieve parasympathetic input from CNIII? What actions does this produce?

Sphincter pupillae – Constricts the pupil, reducing the amount of light entering the eye.

Ciliary muscles – Contracts, causes the lens to become more spherical, and thus more adapted to short range vision.

22

Desrcribe/draw the different branches of the occulomotor nerve and what they innervate

23

Three causes of CNIII lesion

Increasing intracranial pressure – this compresses the nerve against the temporal bone.

Aneurysm of the posterior cerebral artery.

Cavernous sinus infection or trauma.

24

How does a CNIII lesion present clinically?

Ptosis (drooping upper eyelid) – due to paralysis of the levator palpabrae superioris.

Eyeball resting in the ‘down and out‘ location – due to the paralysis of the superior, inferior and medial rectus, and the inferior oblique. The patient is unable to elevate, depress or adduct the eye.

Dilated pupil – due to the unopposed action of the dilator pupillae muscle.

25

How does a lesion of the trochlear nerve present and list some causes

Patients will present with diplopia when looking down and in, such as when reading or going down the stairs

The most common cause is congenital fourth nerve palsy, a condition in which the development of the trochlear nerve or nucleus is abnormal. This may be curable with surgery.

Other causes include diabetic neuropathy, thrombophlebitis of the cavernous sinus and raised intracranial pressure (e.g. due to haemorrhage or oedema) ( in these cases, it is rare for the trochlear nerve to be affected in isolation).

 

26

The trigeminal nerve is associated with derivatives of which pharyngeal arch?

First

27

Describe the different functions of the trigeminal nerve (sensory, motor & parasympathetic)

Sensory: The three terminal branches of CN V innervate the skin, mucous membranes and sinuses of the face. Their distribution pattern is similar to the dermatome supply of spinal nerves (except there is little overlap in the supply of the divisions).

Motor: Only the mandibular branch of CN V has motor fibres. It innervates the muscles of mastication: medial pterygoid, lateral pterygoid, masseter and temporalis. The mandibular nerve also supplies other 1st pharyngeal arch derivatives: anterior belly of digastric, tensor veli palatini and tensor tympani.

Parasympathetic Supply: The post-ganglionic neurones of parasympathetic ganglia travel with branches of the trigeminal nerve. (But note that CN V is NOT part of the cranial outflow of PNS supply)

28

What is the corneal reflex and what does its absence indicate?

The corneal reflex is the involuntary blinking of the eyelids – stimulated by tactile, thermal or painful stimulation of the cornea.

In the corneal reflex, the ophthalmic nerve acts as the afferent limb – detecting the stimuli. The facial nerve is the efferent limb, causing contraction of the orbicularis oculi muscle.

If the corneal reflex is absent, it is a sign of damage to the trigeminal/ophthalmic nerve, or the facial nerve.

29

What are the branches of CN Viii?

Buccal nerve

Inferior alveolar nerve

Auricotemporal nerve

Lingual nerve

30

Where is an inferior alveolar nerve block administered and what are its effects?

The anaesthetic solution is administered at the mandibular foramen, causing numbness of area supplied by the inferior alveolar nerve. The anaesthetic fluid also spreads to the lingual nerve which originates near the inferior alveolar nerve, causing numbness of the anterior 2/3 of the tongue.