Applied Anatomy Of The Cranial Nerves

Question 1

Where does the oculomotor nerve originate from and which two arteries does it run between?

Answer 1

Anterior aspect of the midbrain

Moves anteriorly, passing below the posterior cerebral artery and above the superior cerebellar artery

Question 2

Where does the oculomotor nerve go after the two arteries?

Answer 2

Pierces the dura mater

Enters the lateral aspect of the cavernous sinus

Receives sympathetic fibres from the internal carotid plexus which travel in its sheath but don’t combine

Question 3

Through which fissure does the oculomotor nerve leave the cranial cavity? What happens to it?

Answer 3

Superior orbital fissure

Divides into superior and inferior fibres

Question 4

What does the superior branch of the oculomotor nerve do?

Answer 4

Motor innervation to superior rectus and levator palpebrae superioris

Sympathetic fibres running with it to innervate the superior tarsal muscle

Question 5

What does the inferior branch of the oculomotor nerve supply?

Answer 5

Motor innervation to the inferior and medial rectus and inferior oblique

Parasympathetic fibres to the ciliary ganglion - sphincter pupillae and ciliary muscles

Question 6

What are the causes of a lesion to the oculomotor nerve?

Answer 6

Increase intracranial pressure, compressing it against the temporal bone

Aneurysm of the posterior cerebral artery

Cavernous sinus infection or trauma

Question 7

Clinical signs of oculomotor nerve lesion?

Answer 7

Ptosis due to paralysis of LPS

Eyeball is down and out - paralysis of superior rectus, medial rectus and inferior oblique.

Unable to elevate, depress or adduct the eye

Dilated pupil due to unopposed action of the dilator pupillae

If proximal to the ciliary ganglion, loss of accommodation

If distal to ciliary ganglion, pupils of both eyes will be equal

Question 8

Which is the largest cranial nerve?

Answer 8

Trigeminal nerve

Question 9

What is the trigeminal nerve associated with?

Answer 9

Derivatives of the first pharyngeal arch

Question 10

What is a nucleus?

Answer 10

A collection of nerve cell bodies within the CNS

Question 11

Where does the trigeminal nerve originate from?

Answer 11

Three sensory nuclei -mesencephalic -principle sensory sensory -spinal nuclei of trigeminal nerve

They merge at the level of the pons to form a sensory root

And one motor nucleus (motor nucleus of the trigeminal nerve) extending from the midbrain to the medulla which forms a motor root

Question 12

What is a ganglion?

Answer 12

A collection of nerve cell bodies outside of the CNS

Question 13

What happens to the roots of the trigeminal nerve at the middle cranial fossa?

Answer 13

Sensory root expands into the trigeminal ganglion which is lateral to the cavernous sinus in a depression of the temporal bone called the trigeminal cave

Question 14

What branches does the peripheral aspect of the trigeminal ganglion give rise to?

Answer 14

Ophthalmic (V1)

Maxillary (V2)

Mandibular (V3)

Question 15

What do the divisions of the trigeminal nerve exit the cranium via?

Answer 15

Ophthalmic - superior orbital fissure

Maxillary - foramen rotundum

Mandibular - foramen ovale, entering the infratemporal fossa

Question 16

What are the terminal branches of the ophthalmic nerve?

Answer 16

Frontal

Lacrimal

Nasociliary

Question 17

What does the ophthalmic nerve innervate?

Answer 17

Skin and mucous membranes of derivatives of the frontonasal prominence: -forehead and scalp -cornea -frontal and ethmoidal sinuses -dorsum of nose -upper eyelid and conjunctiva

Question 18

Where is parasympathetic innervation to the lacrimal gland derived from?

Answer 18

Postganglionic fibres from the pterygopalatine ganglion travel with the zygomatic branch of V2 (maxillary) and then join the lacrimal branch of V1

Question 19

What is an absence of the corneal reflex a sign of?

Answer 19

Damage to the trigeminal, ophthalmic or facial nerve

Question 20

What is the route for the corneal reflex?

Answer 20

Stimulation of cornea detected by ophthalmic nerve

Trigeminal ganglion

Trigeminal nerve nucleus in brainstem

Right/left facial nerve via inter-neurones

Orbicularis oculi contracts

Bilateral blinking

Question 21

How many terminal branches does the maxillary nerve have?

Answer 21

14

Question 22

What does the maxillary nerve innervate?

Answer 22

Skin, mucous membranes and sinuses of derivatives of the maxillary prominence of the first pharyngeal arch -lower eyelid and conjucntiva -cheeks and maxillary sinus -nasal cavity and lateral nose -upper lip -superior palate -upper molar, incisor and canine teeth and associated gingiva

Question 23

Where is the parasympathetic supply of the nasal glands derived from?

Answer 23

Post-ganglionic fibres travel with the nasopalatine and greater palatine nerves (branches of V2)

Question 24

What are the terminal branches of the mandibular nerve?

Answer 24

Buccal nerve

Inferior alveolar nerve

Auricotemporal nerve

Lingual nerve

Question 25

Where do the terminal branches of the mandibular nerve arise?

Answer 25

Infratemporal fossa

Question 26

Sensory supply of the mandibular nerve?

Answer 26

Mucous membranes and floor of the oral cavity External ear Lower lip Chin Anterior two thirds of tongue (general sensation) Lower molar, incisor, canine teeth and associated gingiva

Question 27

What motor supply does the mandibular nerve do?

Answer 27

Muscles of mastication Anterior belly of digastric muscle Tensor vali palatini Tensor tympani

Question 28

Parasympathetic innervation of the submandibular and sublingual glands?

Answer 28

Post-ganglionic fibres from the submandibular ganglion derived from the facial nerve, travel with lingual nerve to innervate these glands

Question 29

Parasympathetic supply of the parotid gland?

Answer 29

Post-ganglion fibres from the otic ganglion (derived from glossopharyngeal nerve) travel with the auricotemporal branch to innervate the parotid

Question 30

What is the facial nerve associated with?

Answer 30

Derivatives of the second pharyngeal arch

Question 31

From where and what does the facial nerve begin as?

Answer 31

Arises in the pons Begins as a large motor root and a small sensory root (the branch from the sensory root known as the intermediate nerve)

Question 32

Where do the two roots of the facial nerve travel?

Answer 32

Through the internal acoustic meatus, an opening in the petrous part of the bone, in very close proximity to the inner ear Within the temporal bone, then enter the facial canal which is Z shaped.

Question 33

What happens within the facial canal?

Answer 33

The motor root and sensory root fuse to form the facial nerve which forms the geniculate ganglion Gives rise to the greater petrosal nerve, nerve to stapedius and chorda tympani Then exits the facial canal and cranium via the stylomastoid foramen, just posterior to the styloid process

Question 34

What does the chorda tympani supply?

Answer 34

Taste to anterior two thirds of the tongue

Question 35

What is the first extracranial branch of the facial nerve and what does it innervate? Then where do the next branches go to?

Answer 35

Posterior auricular nerve Motor innervation to some muscles around the ear More branches go to the posterior belly of the digastric and the stylohyoid muscle

Question 36

Where does the facial nerve travel extracranially?

Answer 36

Exits skull, turns superiorly to run anterior to the outer ear Continues to parotid gland where it terminates and splits into branches

Question 37

Name the terminal branches of the temporal nerve What do they innervate?

Answer 37

Temporal Zygomatic Buccal Marginal mandibular Cervical Muscles of facial expression

Question 38

What does the posterior auricular nerve innervate?

Answer 38

Intrinsic and extrinsic muscles of the outer ear Occipital part of the occipitofrontalis muscle

Question 39

What does the temporal branch of the facial nerve innervate?

Answer 39

Frontalis Orbicularis oculi Corrugator supercillii

Question 40

What does the zygomatic branch of the facial nerve innervate?

Answer 40

Orbicularis oculi

Question 41

What does the buccal branch of the facial nerve innervate?

Answer 41

Orbicularis oris Buccinator Zygomaticus

Question 42

What does the marginal mandibular branch of the facial nerve innervate?

Answer 42

Mentalis muscle

Question 43

What does the cervical branch of the facial nerve innervate?

Answer 43

Platysma muscle

Question 44

Which nerve does the chorda tympani hitchhike on?

Answer 44

Lingual nerve

Question 45

What does the greater petrosal nerve do?

Answer 45

Arises in the facial canal Exits temporal bone via middle cranial fossa Through foramen lacerum to pterygopalatine fossa Forms the pterygopalatine ganglion Branches do parasympathetic innervation to -mucous glands of oral cavity, nose and pharynx -lacrimal gland

Question 46

What forms the submandibular ganglion? What does it innervate?

Answer 46

Chorda tympani fibres which combine with the lingual nerve (branch of the trigeminal) Branches travel to the submandibular and sublingual salivary glands

Question 47

What can cause intracranial lesions of the facial nerve?

Answer 47

Middle ear pathology such as a tumour or infection

Question 48

How can you tell if a lesion to the cranial nerve is intracranial or extracranial?

Answer 48

Intracranial: muscles of facial expression are paralysed or weakened and can get other symptoms Extracranial: only get loss of facial muscles

Question 49

What can cause an extracranial lesion of the facial nerve?

Answer 49

Parotid gland pathology eg tumour Infection of the nerve, especially herpes virus Compression from forceps delivery Idiopathic - Bell's palsy

Question 50

Why can compression of the facial nerve happen in a forceps delivery?

Answer 50

Neonatal mastoid process is not fully developed so doesn't provide complete protection of the nerve

Question 51

What does the oculomotor nerve do? (CN III)

Answer 51

Motor and parasympathetic innervation Motor -extra-ocular muscles (except lateral rectus and superior oblique) Parasympathetic -sphincter pupillae and ciliary muscles of the eye

Question 52

Signs/symptoms of damage to the chorda tympani?

Answer 52

Reduced salivation and loss of taste on ipsilateral two thirds of tongue

Question 53

Signs/symptoms if nerve to stapedius is damaged?

Answer 53

Ipsilateral hyperacusis

Question 54

Signs/symptoms of greater petrosal nerve damage?

Answer 54

Ipsilateral reduced lacrimal fluid production