Cranial Nerves VII-XII

Question 1

What four cranial nerves rive from the pons?

Answer 1

Trigeminal
Abducens
Facial
Vestibulocochlear

Question 2

What is the intercranial route of the facial nerve?

Answer 2

Lower pons (junction between pons and medulla)
Enters petrous part of the temporal bone via the internal acoustic meatus
3 branches then arise from this part
It then exits through the base of the skull via the stylomastoid foramen
After exiting, it gives off the 5 extra-cranial branches.

Question 3

What are the three intercranial branches of the facial nerve?

Answer 3

Greater petrosal
Chordi tympani
Nerve to stapedius

Question 4

What are the extracranial branches of the facial nerve?

Answer 4

Temporal
Zygomatic
Buccal 
Marginal Mandibular 
Cervical

Question 5

What are some of the functions of thee facial nerve?

Answer 5

Special sensory - anterior 2/3 of tongue (taste)

Autonomic - lacrimal glands (tears), mucosal glands in nose and roof of mouth, salivary glands (all except parotid)

Motor - facial expression (extracranial), Stapedius muscle

General sensory - Small area of the external ear.

Question 6

What are the two roots of the facial nerve?

Answer 6

Motor root - just motor axons

Nervous intermedius - sensory and parasympathetic axons

Question 7

How do you clinically test facial nerve?

Answer 7

Mainly by testing muscles of facial expression and the corneal reflex.

Question 8

How can different facial nerve lesions present?

Answer 8

They present differently depending on where they are.

Ask about other symptoms e.g: hyperacusis (noise sensitivity), dry eyes, altered taste.

Many other nerves have a close relationship with the facial nerve (e.g. vestibulocochlear) so can present with other nerve symptoms too.

Question 9

What is Bell’s palsy?

Answer 9

A facial nerve palsy

Question 10

What are the afferent and efferents of corneal reflex?

Answer 10

Ophthalmic branch of the Trigeminal = afferent limb of reflex (sensory)
Facial = efferent limb of reflex (motor)

Question 11

Where does the vestibulococular nerve go?

Answer 11

Cochlea and semicircular canals from the vestibular system combine to make the vestibulochchlear nerve.

This travels through the internal acoustic meatus and to the lower pons (junction between the pons and the medulla)

Question 12

What does the vestibulocochlear nerve do?

Answer 12

Special Sensory - Hearing and balance.

Question 13

How do you test vestibulocochlear nerve?

Answer 13

Test hearing and enquire about balance.

Question 14

What places can be damaged that cause hearing loss?

Answer 14

Cochlea, cochlea component of vestibulocochlear nerve or brain stem nucleus.

Question 15

What is an acoustic neuroma?

Answer 15

Benign tumour of Schwann cells surrounding the vestibular component of the vestibulocochlear nerve.

Their physical presence causes compression of the whole nerve ad maybe the CNs in close proximity.

Symptoms and signs include:

• Unilateral hearing loss
• Tinnitus
• Vertigo
• Numbness, pain or weakness down one side of face (Facial nerve / Trigeminal nerve…)

Question 16

What four cranial nerves come from the medulla?

Answer 16

Glossopharyngeal
Vagus
Accessory
Hypoglossal

They are all in the carotid sheath but they quickly exit (except vagus) to go to place high up in head and neck. Only the vagus runs the length of the carotid sheath.

Question 17

What does the glossopharyngeal nerve do?

Answer 17

General sensation - Palatine tonsils and oropharynx
Middle ear and tympanic membrane
Sensory from carotid body and sinus

Special sensory - Taste and general sensation from posterior 1/3 of tongue

Autonomic - parasympathetic innervation to parotid gland

Motor - One muscle - stylopharyngeus - which helps with swallowing

Question 18

How do you test the glossopharyngeal nerve?

Answer 18

Gag reflex (sensory limb) only tested if concerned around swallowing and integrity of nerves involved in this reflex because it is uncomfortable.

It is nor formally tested but when tested, it is tested in conjunction with the vagus nerve because this stimulates the contraction of the muscles in gag reflex.

Isolated lesions of CN IX are rare.

Question 19

Where does the vagus nerve go?

Answer 19

Medulla
Jugular foramen
Carotid sheath
Through neck into thorax and abdomen.

Question 20

What does CN X do?

Answer 20

General sensory - Sensory to lower pharynx and larynx

Motor - Muscles of soft palate, pharynx and larynx

Autonomic - Parasympathetic to thoracic (e.g. heart, tracheobronchial tree) and abdominal viscera.

Question 21

Where does the recurrent laryngeal nerve go?

Answer 21

Carry motor fibres to larynx (so speak)

Left - under arch of the aorta

Right - under right subclavian

Question 22

How do you test the vagus nerve?

Answer 22

Speech, cough and ability to swallow.

Note movements of uvula and soft palate when saying ‘Ahhh’ -uvula would be pulled off centre off centre is issue.

Gag reflex to test the efferent limb.

Injury to its branches e.g. recurrent laryngeal nerve following thyroid surgery can cause hoarseness and dysphonia.

Question 23

What does the spinal accessory nerve do?

Answer 23

Motor - SCM and trapezius

Question 24

Where does accessory nerve go?

Answer 24

Emerges through the jugular foramen and passes deep to SCM and provides its motor innervation.

It then runs posteriolaterally across posterior triangle.

It enters deep into trapezius and provides its motor innervation.

Question 25

How do you test CN XI?

Answer 25

Shrug shoulders against resistance (trapezius)

Turn head against resistance (sternacleidomastoid)

Question 26

In what area is CN XI susceptible to injury?

Answer 26

Posterior triangle because it is quite superficial.

Question 27

What does CN XII do?

Answer 27

MMotor - muscles of tongue (all except one)

Question 28

Where is it?

Answer 28

Runs medial to angle of mandible. Crosses internal and external carotid arteries in the neck.

Can’t see it unless move mandible

Question 29

How do you test CN XII?

Answer 29

Inspect and movement the tongue

Question 30

How would damage to the hypoglossal nerve present?

Answer 30

Weakness and atrophy of the tongue muscle on the ipsilateral side.

It is rare.