Cranial nerves

Question 1

CN I

Answer 1

• Olfactory nerve
• FIbers arise as central processes of the olfactory cells of nasal mucosa
• Traverse cribriform to join olfactory bulb
• Filaments surrounded by meningeal sheaths enclosing extension of the subarachnoid space so infection

Question 2

CN II

Answer 2

• Optic nerve
• Connects retina to diencephalon
• Optic chiasm- decussation
• To OPTIC FORAMEN
• Enclosed within extension of meninges and dura blends with sclera where nerve joins eyeball

Question 3

CN III

Answer 3

• Oculomotor nerve
• Consists of somatic efferent fibers from motor nuc and visceral efferent from parasymp nuc- both are in tegmentum
• Fibers from both emerge from ventral aspect of midbrain
• Nerve travels close to trochlear, abducent and ophthalmic nerves to the cavernous sinus and then through ORBITAL FISSURE
• Divides in orbit to supply dorsal, medial, and ventral recti, ventral oblique and levator muscle of upper eyelid
• Pregana parasymp fibers synapse within the small ciliary ganglion placed on one of the branches then postgang fibers pass within short ciliary nerves to supply intraocular and CONSTRICTOR pupillae muscles

Question 4

CN IV

Answer 4

• Trochlear nerve
• Provides somatic efferent innervation to the dorsal oblique muscle
• Nuc of origin within the tegmentum gives rise to fiber bundle that decussates internally before emerging from rostral medullary velum
• Passes through ORBITAL FISSURE

Question 5

CN V

Answer 5

• Trigeminal nerve
• Sensory to the skin and deeper tissues of the face
• Motor innervation to muscles of first pharyngeal arch

Question 6

CN V- proprioceptive and exteroceptive afferent fibers

Answer 6

• Pass to the rostral trigeminal mesencephalic nuc
• Other exteroceptive afferent fibers synapse onto the pontine and spinal trigeminal nuclei

Question 7

CN V- efferent fibers

Answer 7

• Originate in trigeminal motor nucelus

Question 8

How is CN V peripheral nerve formed?

Answer 8

• Fusion of sensory and motor roots that attache to ventrolateral aspect of pons

Question 9

What does the sensory portion of CN V become?

Answer 9

• Sensory root carries massive trigeminal ganglion and then divides into ophthalmic, maxillary and mandibular
• Mandibular- unites with motor root and is a mixed nerve
• O and Max remain sensory only

Question 10

Where do the branches exit for CN V?

Answer 10

• Mand: OVAL FORAMEN
• O: ORBITAL FISSURE
• Max: ROUND FORAMEN

Question 11

What are the basic territories for each branch of CN V?

Answer 11

-O: frontonasal process, primordium of forehead and nose regions
- Max: maxillary process, primordium of the upper jaw and associated parts
- Mand: mandibular process, primordium of lower jaw and masticatory and first pharyngeal arch muscles

Question 12

What are the three branches of O nerve of CN V?

Answer 12

• Lacrimal: lateral part of the orbital perimeter and supplies the skin about the lateral angle of the eye
• Frontal: upper eyelid, forehead, mucosa of frontal sinus
• Nasociliary nerve: infratrochlear- supplies structures at medial angle and another portion of the mucosa of frontal sinus, long ciliary nerves- penetrate posterior aspect of eyeball (cornea), ethmoid- medial and lateral branches to mucosa

Question 13

Maxillary nerve of CN V:

Answer 13

• Runs across the wall of the pterygopalatine fossa ventral to the orbit
• Lies close to pterygopalatine ganglion
• enters infraorbital canal at MAXILLARY FORAMEN - know as infraorbital n.
• Zygomatic n- supplies lower eyelid and skin
• Pterygopalatine n- lesser goes to soft and greater goes to hard, palatine mucosa and floor of nasal vestibule
• Caudal nasal n.- passes through pterygopalatine foramen to supply mucosa of the ventral part of nasal cavity, maxillary sinus and palate

Question 14

What does the infraorbital nerve of CN V do?

Answer 14

• Continuation of maxillary n.
• some to the alveoli of the cheek teeth and nasal mucosa and then some branches that continue in the bone to the canine and incisor teeth
• Emerges from infraorbital foramen and supplies various labial and nasal branches to structures of muzzle

Question 15

Mandibular nerve of CN V:

Answer 15

• Branches pass to masseter, temporalis, medial and lateral pterygoid, tensor veli palatini and tensor tympani muscles
• Masseteric nerve- passes to masseter muscle between coronoid and condylar processes of mandible
• Deep temp n to temporalis
• Buccal n. - sensory to tissues of the cheek
• Auriculotemporal n. - enters face and snesory to skin of the temporal region and external ear
• Transverse facial branch - supplies trip of skin to the corner of the mouth
• Lingual n - oropharyngeal mucosa before dividing into a deep branch that enters tongue- sublingual nerve
• Inferior alveolar n- supply motor innervation to mylohyoideus and rostral belly of digastricus before entering mandibular canal via mand foramen
• supplies sensory innervation to lower cheek teeth before reappears as mental nerve - supplies tissues of lower lip and chin

Question 16

What does the sublingual nerve join with?

Answer 16

• Joined by chorda tympani- branch of facial - contains axons of pregana visceral efferent fibers to salivary gland that synapse in the adjacent mandibular ganglion as well as gustatory fibers innervating the taste buds of rostral 2/3rds of tongue

Question 17

CN VI

Answer 17

• Abducent
• Fibers originate within caudal brainstem and emerge from brain close to midline
• Travel intracranially to the ORBITAL FISSURE
• In the orbit- nerve divides into a branch to lateral rectus and one to retractor

Question 18

CN VII

Answer 18

• Facial
• Has senosry and motor function
• Facial and vestibulococh arise close at the lateral extremity of trapezoid body
• Two nerves run through common meningeal covering to the internal acoustic meatus of the petrous temporal bone
  Facial nerve enters facial canal within the bone that leads to the stylomastoid foramen
• contains the geniculate ganglion
• In facial canal- greater petrosal nerve - emerges through independent foramen - initially just has parasymp axons but then joined by symp axons
• Stapedial- motor
• Chorda tympani- incorporates with lingual branch

Question 19

What is the course of the nerve of the pterygoid canal of CN VII

Answer 19

• Runs through pterygoid canal to reach the pterygopalatine gang within the fossa

Question 20

What happens after facial nerve emerges from stylomastoid foramen?

Answer 20

• First branch is internal and caudal auricular nerves - supply muscles of external ear and branches to hyoid muscles and caudal belly of digastricus
  Three branches- auriculopalpebral, dorsal and ventral buccal nerves

Question 21

Auriculopalpebral nerve of CN VII

Answer 21

• Crosses zygomatic arch, traveling toward the space between upper eyelid and external ear before dividing in to branches that supply muscles of eyelids (NOT LEVATOR PALP SUP) and auricular muscles in front of external ear
• Produce dropping of external ear and narrow palpebral fissure with inability to close eye

Question 22

Dorsal and ventral buccal branch of CN VII

Answer 22

• Crosses masseter en route to muzzle
• ventral - more ventral than dorsal
• muscles of cheeks, lips and nostrils
• food may collect in vestibule

Question 23

CN VIII

Answer 23

• Vestibulocochlear
• Divides intracranially at internal acoustic meatus into vest and coch parts
• separate to petrous temporal bone to vest and coch components of inner ear

Question 24

CN IX

Answer 24

• Glossopharyngeal
• FIbers that innervate structures of thrid phar arch origin with imp parasymp and afferent comp
• Motor to part of the palatophary musculature and salivary glands
• Sensory to tongue palate and pharynx
• Runs with vagus and accessory to jugular foramen and then has two small ganglia here
• Tympanic n.- participates with branches of facial and internal carotid forming a plexus from which a nerve lead to otic gang for supply of parotid
  Carotid sinus branch - terminates with baroreceptors in sinus wall and chemoreceptors
• Pharyngeal branch- stylopharyngeus caudalis and then pharyn plexus - sensory and motor
• Lingual branch - with artery, lingual branch of mand n., hypoglossal nerve
• sensory to mucosa of tongue and motor to levator palatini muscle and glands of soft palate

Question 25

CN X

Answer 25

- Vagus - nerve of fourth phary arches - COntains parasymp fibers that innervate cervical, thoracic and abd viscera - JUGULAR FORAMEN - RUns with glosso and accessory - goes to cranial cervical ganglion - continues down neck with symp trunk - left vagosymp in contact with eso - diverge at entrance to chest and vagus goes to mediastinum - Auricular branch - innervation of skin of external ear - Pharyngeal branch- cervical eso - cranial laryngeal n- goes to larynx - cricothyroid and internal branch for laryngeal mucosa

Question 26

What is the course of the recurrent laryngeal nerve?

Answer 26

- detached within the thorax - right side- winds around branch of subclavian a - Left- winds around aorta - reascends the neck ventral to common carotid in a course that leads back to larynx where it supplies bulk of the intrinsic laryngeal musculature (except cricothyroideus) and mucosa caudal to the glottis

Question 27

CN XI

Answer 27

- Accessory - spinal root provided by axons that emerge midway between dorsal and ventral roots of first five spinal nerves - enters skull through foramen magnum passes through jugular foramen to divide into dorsal and ventral - dorsal: caudally of splenius and serratus ventralis before supplies brachiocephalicus, omotransversarius and trapezius - ventral- sternocephalicus

Question 28

CN XII

Answer 28

- Hypoglossal - Motor to intrinsic and extrinsic muscles of tongue - tongue deviates to normal side