L38 Cranial Nerves Part 2

Question 1

Trigeminal (V) nerve

Purpose:

Composition:

Region/tissues supplied:

Foramen, fissure or canal it passes through:

Answer 1

Mainly sensory nerve with some motor components ( the motor component is that it supplies the muscles for mastication (chewing)).

It is the principle somatic sensory( touch,pain,temperature) nerve for the face & head.

(The name comes from 3 - “tri” and origin - “germinal”). The trigeminal nerve has 3 nerve divisions:

Ophthalmic (V1) nerve [this passes through superior orbital fissure)

Maxillary (V2) nerve [this passes through the foramen rotundum]

Mandibular (V3) nerve [this passes through the foramen ovale]

Question 2

What are the 3 Trigeminal Divisions and what are they associated with?

Answer 2

Ophthalmic, Maxillary and Mandibular!

Ophthalmic - somatic sensation of skin of the forehead, upper eyelid, cornea surface & inside the eye.

Maxillary- from the skin of the lower eyelid, cheek + upper teeth and nasal mucosa.

Mandibular- from skin & teeth of lower jaw + tongue & also contains motor output to the chewing muscles ( e.g Masseter, temporalis)

Question 3

What is a simple check to test the ophthalmic nerve function?

Answer 3

Corneal- eyeblink reflex

Question 4

Facial (VII) nerve

Purpose:

Composition:

Region/tissues supplied:

Foramen, fissure or canal it passes through:

Function(s) & simple tests:

Effects of nerve damage/lesions:

Answer 4

It has a sensory, motor and autonomic composition.

Main function: motor supply (which comes from main motor nucleus in the pons) for all facial muscles used for facial expressions including some near the eyes (e.g obicularis oculi, frontalis).

Sensory component: from taste buds on anterior 2/3 of tongue ( salt, sweet,sour).

Parasympathetic (autonomic bit) component of nerve: supplies lacrimal gland (tear production) via pterygopalatine ganglion + submandibular and sublingual salivary glands via geniculate ganglion.

Foramen: internal auditory /acoustic meatus

Question 5

What does damage to the main motor part of the facial nerve cause?

Answer 5

Bell’s palsy

Question 6

What does the obicularis oculi do?

Answer 6

It closes the eyelids when you blink, spreading the tear film over the cornea. (Keeps the cornea hydrated- avoids dry eyes and cracking which cornea more susceptible to erosions and infections which can later cause blindness)

Question 7

Generally how do circular muscles like the obicularis oculi work?

Answer 7

Circular muscles they tend to act like sphincter , when contracted the circle gets narrower.

Question 8

How can we test for Bell’s palsy?

Answer 8

Ask someone to look up and show their teeth.

Bell’s palsy patients have:

Paralysed muscles (unable to raise eyebrow or show teeth on affected side)[lower eyelid droop due to paralysis of obicularis oculi which means that it isn’t contracting]

Question 9

What conditions of the eye are associated with Bell’s palsy and how are they treated?

Answer 9

1. Upper eyelid palsy- insert gold weight
   - most of the time the eye is open because of the obicularis oculi thus adding gold weight allows voluntary relaxation of the LPS ( levator palpebrae superioris) as eye is forced closed under gravity.
2. Everted (droopy) lower eyelid - tighten the eyelid surgically.
   - reducing lower lid length prevents drooping and avoids lateral pool of tears forming.
3. Dry Eyes - treated by lubricating drops or ointment.
   In extreme cases moisture chamber shields can be used which are like humidifiers that allow the eye to stay damp and are attached to spectacle frames to lessen tear evaporation.

Question 10

Vestibulo-Cochlear (VIII) Nerve

Purpose:

Composition:

Region/tissues supplied:

Foramen, fissure or canal it passes through:

Function(s) & simple tests:

Effects of nerve damage/lesions:

Answer 10

Purely sensory nerve (originated from inner ear which is housed in petrous portion of temporal bone)

There are two main components:

• cochlear nerve: carries hearing/auditory information
• Vestibular nerve: carries information regarding the position and movement of the head.

Foramen: internal auditory/acoustic meatus

Vestibular dysfunctions include loss of VOR (vestibular ocular reflex - the world spinning around— oscillopsia)

Damage to the cochlear nerve causes 2 types of hearing loss - conductive and sensory neural hearing loss.

Question 11

How is sound heard?

Answer 11

Outer and middle ears convert and amplify air pressure (sound) waves at (tympanic membrane) ear drum & via the ossicles (hammer, anvil and stirrup- three smallest bones in the body) into mechanical movements of auditory receptors (hair cells) in the cochlea (inner ear) innervated by ‘spiral’ (cochlea) ganglion cells.

Question 12

Describe simple tests of auditory function

Answer 12

Using Otoscope/Auriscope. (auditory equivalent of ophthalmoscope to check for ear wax build up etc,).

Question 13

What is a normal hearing range?

Answer 13

20Hz to 20kHz

Question 14

What are the two types of hearing loss?

Answer 14

1) Conductive hearing loss - affects outer or middle ear

2) Sensory-Neural hearing , hair cell damage hearing loss- severe an irreversible!

Question 15

Describe common cause of conductive hearing loss?

Answer 15

ear wax , ‘glue ear’.

condition is often reversible

Question 16

In conductive hearing loss is sound detection via mastoid bone affected?

Answer 16

No

Question 17

In sensory neural hearing loss is sound detection via mastoid bone affected?

Answer 17

Yes - it is absent as hair cells in cochlea are affected.

Question 18

Why is sensory neural hearing loss irreversible?

Answer 18

Hair cells ( the neural apparatus in this case) are damaged and the body does not regenerate neurones.

Question 19

What can cause sensory neural hearing loss?

Answer 19

Excess exposure to loud noise.
Some antibiotics can cause hearing loss.
Age related hearing loss - its called presbycusis.

Question 20

What’s presbycusis?

Answer 20

Age related hearing loss

Question 21

What is the vestibule comprised of?

Answer 21

The Utricle and Saccule

Question 22

What do the Utricle and saccule contain?

Answer 22

Hair cells which monitor head position with respect to gravity.

Question 23

What is a test of correct functioning of the vestibule?

Answer 23

That the eye-righting reflex is intact i.e. eyes rotate when you tilt your head.

Question 24

What are the names of the three semi-circular canals in the ear?

Answer 24

Posterior, Anterior and Horizontal.

Question 25

What do hair cells in the semi-circular canals do?

Answer 25

Hair cells in the semi-circular canals monitor angular head acceleration & deceleration in 3D.

Question 26

How can one test the fucntion of the Semi-circular canals?

Answer 26

Check for the Vestibular-Ocular Reflex (VOR).

i.e. that eyes move opposite to head turn

Question 27

Glossopharyngeal (IX) nerve

Purpose:

Composition:

Region/tissues supplied:

Foramen, fissure or canal it passes through:

Answer 27

(Name denotes where it roughly is glottis is at the back of your throat as is the pharynx and so is associated with that part of your body).

The nerve has a sensory, motor and autonomic composition.

It’s main function is motor, from Nucleus Ambiguous (from medulla (oblongata) in brainstem) to stylopharyngeal muscles which elevate larynx for swallowing.

Sensory component of the nerve is responsible for somatic sensation from pharynx and posterior third of tongue + taste buds (bitter).

Parasympathetic component of nerve supplies Otic ganglion which syupplies the parotid salivary gland (largest salivary gland).

Foramen: Jugular foramen (where internal jugular vein also passes through).

Question 28

Which saliavry gland is responsible for the aqueous component of your saliva?

Answer 28

Parotid Salivary Gland.

Question 29

How to test if the Glossopharyngeal (IX) nerve is functioning correctly?

Answer 29

Test for a gag reflex.

Question 30

Vagus (X) nerve

Purpose:

Composition:

Region/tissues supplied:

Foramen, fissure or canal it passes through:

Answer 30

The nerve has a sensory, motor and autonomic composition.

One of its Main function: is it’s motor function from Nucleus Ambiguous to muscles of the pharynx, soft palate & larynx controlling swallowing and speech (recurrent laryngeal nerve to vocal cords).

Sensory part of the nerve is responsible for somatic sensation from the same region as well as from thoracic and abdominal organs).

Other Main Function: Parasympathtic , widespread to all thoracic and abdominal organs (for resting and digesting).

Foramen: Jugular Foramen.

Question 31

How can we test the motor function of the vagus (X) nerve be tested?

Answer 31

Lesions of recurrent laryngeal nerve results in hoarse speech.

Question 32

What two cranial nerves pass through ONLY the jugular foramen?

Answer 32

The Vagus (X) nerve and Glossopharyngeal (IX) nerve both pass through the jugular foramen. (The Accesory (XI)Nerve passes through jugular formane AND Foramen Magnum).

Question 33

Accessory (XI) Nerve:

Purpose:

Composition:

Region/tissues supplied:

Foramen, fissure or canal it passes through:

Answer 33

The Acessory (XI) nerve has a purely motor composition and is made up of 2 divisions - the larger and smaller division.

The larger division- mainly supplies sternocleidomastoid muscle (which rotates head away) & trapezius muscle ( which lifts shoulders).

The smaller division - supplies some input to internal laryngeal and soft palate for speech production.

Foramen: Jugular foramen and Foramen Magnum.

Question 34

What does a lesion in the Accesory (XI) nerve cause?

Answer 34

Difficulty in rotating the head toward the opposite side (sternocleidomastoid) and in elevating the shoulder on the affected side (trapezius).

Question 35

Hypoglossal (XII) Nerve:

Purpose:

Composition:

Region/tissues supplied:

Foramen, fissure or canal it passes through:

Answer 35

It has a purely motor composition.

Hypoglossal Nucleus supplies intrinsic and extrinsic muscles of the tongue, movement for eating and speech production.

Foramen: Hypoglossal Canal

Question 36

What does a lesion of the Hypoglossal (XII) nerve cause?

Answer 36

Spasms/’fasciculation’ (both mean the same thing) of the intrinsic muscles on the affected side & deviation toward the affected side on tongue extension due to paralysis/weakness of intrinsic muscles. (AKA tongue muscle spasms and your tongue being slanted to one side when you stick your tongue out. If lesion is on right side your tongue will slant right!).

Question 37

What’s the difference between an intrinsic and extrinsic muscle in the tongue?

Answer 37

Rolling your tongue up contracts intrinsic muscles.

Sticking your tongue out contracts extrinsic muscles.

Question 38

Cells in which of these ganglia directly innervate the lacrimal gland?

Answer 38

Pterygopalatine