Clinical Anatomy of Cranial Nerve Testing

Question 1

List the ‘12’ Cranial Nerves and their modalities

Answer 1

CN I olfactory nerves (special sensory)

CN II optic nerves (special sensory)

CN III oculomotor nerves (motor & parasympathetic)

CN IV trochlear nerves (motor)

CN V trigeminal nerves (CN V1 & V2: sensory only*; V3 is sensory & motor*)

CN VI abducent nerves (motor)

CN VII facial nerves (special sensory; motor & parasympathetic)

CN VIII vestibulocochlear nerves (special sensory)

CN IX glossopharyngeal nerves (special sensory; sensory; motor & parasympathetic)

CN X vagus nerves (sensory; motor; parasympathetic)

CN XI spinal accessory nerves (motor)

CN XII hypoglossal nerves (motor)

Question 2

Which part of the CNS do each originate from?

Answer 2

Forebrain - I, II

Midbrain - III, IV

Pons - V

Pontomedullary junction - VI, VII, VIII

Medulla - IX, X, XII

Spinal cord - XII

Question 3

Label from view superior to cranial fossae

Answer 3

Question 4

Through which cranial fossa do each of the Cranial nerves leave the crainial cavity?

Answer 4

Anterior fossa - CN I

Middle fossa - CN II, III, IV

Posterior fossa - CN V - CN XI

Foramen magnum - CN XII

Question 5

Describe the divisions of the trigemninal nerve

Answer 5

3 divisions

• Ophthalmic (CNV1) – sensory
• Maxillary (CNV2) – sensory
• Mandibular (CNV3) – sensory and motor

Question 6

Describe and detail the course of the Trigeminal Nerve

Answer 6

CNS connection:

The only CN to attach to the pons (laterally, midway between midbrain & medulla)

Intracranial Course:

inferior to the edge of the tentorium cerebelli between the posterior and middle cranial fossae

Skull Base Foramen:

• CN V1 - superior orbital fissure
• CN V2 - foramen rotundum
• CN V3 - foramen ovale

Extra-cranial Course:

• Sensory axons from all 3 divisions course, from the superficial and deep structures of the face, posteriorly, towards their respective base of skull foraminae
• motor axons from CNV3 course from the foramen ovale towards the skeletal muscle they supply

Question 7

Label the somatic sensory innervation to the head

Answer 7

Question 8

CN V1 deep sensory territory?

Answer 8

• bones & soft tissues of the orbit (except the orbital floor & lower eyelid)
• the upper anterior nasal cavity
• all paranasal sinuses (except the antrum)
• the anterior & posterior cranial fossae

Question 9

CN V2 deep sensory territory?

Answer 9

• the lower posterior nasal cavity
• the maxilla & maxillary sinus (antrum)
• the floor of the nasal cavity/palate
• the maxillary teeth & associated soft tissues (gingivae & mucosae)

Question 10

CN V3 deep sensory territory?

Answer 10

• the middle cranial fossa
• the mandible
• the anterior 2/3rds of the tongue
• the floor of the mouth
• the buccal mucosa
• the mandibular teeth & associated soft tissues

Question 11

Name and detail the muscles of masstication

Answer 11

Close Jaw

• Masseter
• Temporalis
• Medial Pterygoid

Open Jaw

-Lateral Pterygoid

Question 12

Describe the origin and attachments to the muscles of masstication

Answer 12

Masseter - Angle of mandible - Aygomatic arch

Temproalis - coronoid process of mandible - lateral aspect of neurocranium

Medial Pterygoid - Medial mandible - Pterygoid plates fo the sphenoid bone

Lateral Pterygoid - Condyle of mandible and articular disc of TMJ - Pterygoid plates of the spenoid bone

Question 13

List the key areas for testing the sensory afferent of the Trigmeninal Nerve

Answer 13

• Ophthalmic (CNV1):
• forehead, upper eyelid & tip of nose
• Maxillary (CNV2):
• mid-cheek, lower eyelid, upper lip & nostril of nose
• Mandibular (CNV3):

Question 14

How would you clinically test the Sensory afferent of the trigemnial nerve?

Answer 14

1. Ask the patient to close their eyes
2. Gently brush the skin in each dermatome with a fine tip of cotton wool
3. Ask the patient to tell you when they feel their skin being touched
4. Compare the 2 sides

Question 15

How would you clinically test the motor efferent of the trigeminal nerve?

Answer 15

1. Palpate the strength of contraction of the masseter & temporalis by asking patient to clench their teeth
2. Ask the patient to open their jaw against resistance

Question 16

Describe and detail the course of the Facial Nerve

• Connection to the CNS
• Intracranial course
• Base of skull exit
• Extracranial Course

Answer 16

Connection to the CNS

-anterolateral at pontomedullary junction

Intracranial course

-directly into internal acoustic meatus in the posterior cranial fossa

Base of skull exit

• internal acoustic meatus of the temporal bone
• stylomastoid foramen

Extracranial Course

-most somatic motor axons pass into the parotid gland then into 1 of the 5 branches that supply the muscles of facial expression

Question 17

Label the diagram of facial nerve course

Answer 17

Question 18

Label the facial nerve diagram

Answer 18

Question 19

Label and detail the muscles of facial expression

Answer 19

Question 20

Describe and detail the course of the Glossopharyngeal nerve

• Connection to the CNS
• Intracranial course
• Base of skull exit
• Extracranial Course

Answer 20

Connection to the CNS

-lateral aspect of superior medulla oblongata

Intracranial course

-directly towards jugular foramen in the posterior cranial fossa

Base of skull exit

-junction between temporal bone & occipital bone – jugular foramen

Extracranial course

-axons mainly pass to or from the tongue and palate

Question 21

List the modalities of the glossopharyngeal nerve

Answer 21

General somatic sensory

Special sensory

Visceral afferent

Somatic motor

Parasympathetic (secretomotor)

Question 22

List the general sensory of the glossopharyngeal nerve

Answer 22

• the posterior 1/3rd of the tongue
• the mucosa of most of the nasopharynx
• the mucosa of all of the oropharynx
• the mucosa of some of the laryngopharynx (some overlap with CN X territory)
• the palatine tonsil
• the eustachian tube
• the middle ear cavity

Question 23

List the special sensory of the glossopharyngeal nerve

Answer 23

•the vallate papillae (with taste buds) of the posterior 1/3rd of the tongue

Question 24

List the visceral afferent of the glossopharyngeal nerve

Answer 24

visceral afferent to the carotid sinus baroreceptors & the carotid body chemoreceptors

(carotid massage relevance)

Question 25

List the somatic motor of the glossopharyngeal nerve

Answer 25

Somatic motor to 1 of the longitudinal muscles of the pharynx (stylopharyngeus)

Question 26

List the autonomic of the glossopharyngeal nerve

Answer 26

parasympathetic (secretomotor) to the parotid salivary gland

Question 27

Describe and detail the course of the Vagus nerve - Connection to the CNS - Intracranial course - Base of skull exit - Extracranial Course

Answer 27

Connection to the CNS -lateral aspect of medulla oblongata, immediately inferior to CN IX Intracranial course -directly towards jugular foramen in the posterior cranial fossa Base of skull exit -junction between temporal bone & occipital bone – jugular foramen Extracranial Course -axons supply lots of structures between the palate and the midgut

Question 28

List the contents of the carotid sheath

Answer 28

Common Carotid Artery Internal Jugular Vein Vagus Nerve Deep Cervical lymph nodes

Question 29

Describe the course of the Vagus Nerve in the thorax (right and left)

Answer 29

Both Nerves pass posterior to the lung roots and onto the surface of the oesophagus Both pass through the diaphragm with the oesophagus Branches pass into stomach, the celiac and superior mesenteric ganglia Supply foregut and midgut up until splenic flexure of colon

Question 30

How do we clinically test the vagus nerves?

Answer 30

-ask patient to say ‘ah’ – also tests CNV3 motor function uvula should lift straight up in midline unilateral pathology will pull uvula away from the non-functioning side -ask patient to swallow small amount of water watch larynx movement splutter may suggest abnormal swallow -listen to speech hoarseness may suggest abnormal function of muscles of larynx -ask patient to cough remember also requires diaphragm

Question 31

Describe and detail the course of the Spinal Accessory nerve - Connection to the CNS - Intracranial course - Base of skull exit - Extracranial Course

Answer 31

Connection to the CNS - via cervical spinal nerve anterior rootlets to the spinal cord Intracranial course -ascends through foramen magnum then travels towards jugular foramen in posterior cranial fossa Base of skull Exit -junction between temporal bone & occipital bone Extracranial Course -axons supply sternocleidomastoid on deep surface, then continue across the posterior triangle of the neck deep to the investing fascia and supply the trapezius

Question 32

Label the course of the Spinal Accessory Nerve

Answer 32

Question 33

Describe and detail the course of the Hypoglossal nerve - Connection to the CNS - Intracranial course - Base of skull exit - Extracranial Course

Answer 33

Connection to the CNS - via many rootlets that attach lateral to the pyramids of the medulla oblongata Intracranial course -passes anteriorly towards hypoglossal canal in the posterior cranial fossa Base of skull Exit -hypoglossal canal (anterior wall of foramen magnum) Extracranial Course - descends in neck lateral to carotid sheath - at level of hyoid bone it passes anteriorly towards the lateral aspect of the tongue - supplies most of the muscles of the tongue

Question 34

How do we clinically test the SPinal Accessory Nerve?

Answer 34

Clinical testing: - ask patient to stick tongue straight out - if both CNXII’s are functioning normally the tongue tip remains in the midline on protrusion - if there is unilateral CN XII pathology the tongue tip will point towards the side of the injured nerve

Question 35

Summary of Cranial Nerve clinical Investigations

Answer 35