Cranial Nerves Continued

Question 1

GSE

Answer 1

General Somatic Efferent: motor fibers to skeletal musculature (VOLUNTARY)

Question 2

GSA

Answer 2

General Somatic Efferent: motor fibers to skeletal musculature (VOLUNTARY)

Question 3

GVE

Answer 3

General Visceral Efferent: motor fibers to smooth muscle, glands, and viscera (INVOLUNTARY)

Question 4

GVA

Answer 4

General Visceral Afferent: fibers that carry visceral sensation

Question 5

BE/SVE

Answer 5

Branchial Efferent/Special Visceral Efferent: motor fibers to skeletal, voluntary muscles that developed from branchial (pharyngeal) arches

Question 6

SVA

Answer 6

Special Visceral Afferent: taste & smell

Question 7

SSA

Answer 7

Special Somatic Afferent: vision, hearing & balance

Question 8

Parasympathetic GVE fibers reside ONLY in what nerves? And what are their associated ganglion?

Answer 8

CN III: Oculomotor
CN VII: Facial
CN IX: Glossopharyngeal
CN X: Vagus

CN III = Ciliary Ganglion
CN VII = Pterygopalatine & Submandibular Ganglion
CN IX = Otic Ganglion
CN X = Various ganglia near visceral organs

Question 9

Branchial Motor (BE/SVE) fibers reside ONLY in nerves associated with what? What are they?
(see chart on slide 7)

Answer 9

pharyngeal (branchial) arches

I –> CN V3 (mastication)
II –> CN VII (facial expression)
III –> CN IX (?)
IV –> CN X (pharyngeal constrictors- swallowing to move bolus to esophagus)
VI –> CN X (larynx muscles - voice box)

Question 10

CN V - trigeminal nerve pathway:

Answer 10

Pathway:
Begins at pons and travels superiorly/anteriorly towards face
Splits into three terminal divisions at “trigeminal ganglion” in middle cranial fossa

V1 = Ophthalmic (upper face)
V2 = Maxillary (mid face)
V3 = Mandibular (lower face)

Each terminal branch exits the skull via a different foramen and innervates a different region of the face

BE/SVE Modality
Arch 1
Muscles of mastication

Question 11

What are the 3 Trigeminal Sensory Nuclei and what are their actions?

Answer 11

1.) Spinal nucleus of the trigeminal nerve: Pain the Tem & light touch.
2.) Chief or principal nucleus or main sensory nucleus: discriminative sensation and light touch as well as conscious proprioception.
3.) Mesencephalic nucleus: proprioception

Question 12

CN V1= Ophthalmic pathway

Answer 12

Pathway: Ophthalmic division passes through the cavernous sinus, exits via superior orbital fissure, & has many additional branches from there
Foramina: Superior orbital fissure

Function: GSA Modality
General sensory to:
forehead
anterior scalp
upper eyelid
tip of the nose
anterior nasal cavity
frontal & ethmoidal sinuses
dura mater of anterior cranial fossa

Question 13

How do you test CN V1?

Answer 13

Test sensation of forehead
CN V1 – corneal reflex

Question 14

V2 = maxillary pathway:

Answer 14

Pathway: passes through the cavernous sinus, exits skull via foramen rotundum to innervate face

Foramina: Rotundum

Function: GSA Modality
General sensory to:
the sides of the nose
lower eyelids
upper lip
posterior nasal cavity
teeth of the upper jaw
maxillary sinus
nasopharynx
palate
dura of the middle cranial fossa

Question 15

What is the function of CN V2?

Answer 15

Test sensation of lateral nose, cheek and upper jaw

Question 16

CN V3 = mandibular pathway (lower face):

Answer 16

Pathway: not associated with cavernous sinus, exits skull via foramen ovale to innervate lower face

Foramina: Ovale

Function: GSA Modality
General sensory to:
lower lip
chin
lower face & cheek
anterior external ear
teeth of mandible
mucous membranes of cheek
anterior 2/3 of tongue
dura in the middle cranial fossa

Question 17

CN V extensively innervates __________ mater. Causing what?

Answer 17

dura mater

Headache due to referring pain from some pathological conditions in the head region!

Question 18

V3 = mandibular pathway (arch 1 and mastication)

Answer 18

Foramina: Ovale

Function: BE/SVE Modality
Arch 1
Voluntary motor control to muscles of mastication
Temporalis
Masseter
Medial pterygoid
Lateral pterygoid

Collectively these muscles open/close the mandible for chewing action

Question 19

What muscle contracts primarily to dampen the noise produced by chewing? Of CN V?

Answer 19

tensor tympani muscle

The tensor tympani muscle, innervated by the mandibular branch of CN V, connects the auditory tube to the malleus handle. It increases the tension in the tympanic membrane, thus protecting it from excessive vibration in response to loud sounds.

Question 20

What is trigeminal neuralgia?

Answer 20

Neuralgia: sensation of pain elicited without presence of noxious stimuli
Often develops without any cause
Intermittent attacks of severe, sharp, stabbing pain “electric shock”
Most often affects CN V2 and V3
Affects GSA code only*
No motor deficits
Unilateral distribution
Seen m/c in females (50+)

Aggravated by:
Exposure to cold
Chewing
Brushing teeth
Talking
Touching face

Treatment usually involves medications which block incoming pain signals into CNS

Question 21

VII = Facial nerve

Fiber types? Foramina?

Answer 21

FIBER TYPES OF FACIAL NERVE:
(BE/SVE, SVA, GVE, GSA)

1.) BE/SVE axons to muscles of facial expression (arch II)

2.) SVA axons (taste) from the anterior 2/3rds of the tongue

3.) GVE axons to the submandibular, sublingual and lacrimal glands

4.) GSA axons for the “patch” of skin behind the ear

Foramina: Internal acoustic meatus AND Stylomastoid

Question 22

What is the pathway of CN VII Facial Nerve?

Answer 22

Pathway:
Facial nerve originates from the pons and first exits skull through the internal acoustic (auditory) meatus winding through the petrous portion of the temporal bone (facial canal)
Infection in the middle/inner ear can impact CN VII
Within temporal bone, nerve gives off several intracranial branches
Remaining nerve will exit the cranial base via the stylomastoid foramen.
Foramina: Internal Acoustic Meatus AND Stylomastoid Foramen
Once nerve exits skull – it gives rise to 6 extracranial branches

Question 23

What are the intracranial branches of the facial nerve VII?

Answer 23

Intracranial branches:

Chorda tympani carries GVE and SVA
Branches off main nerve in the facial canal (inside skull)
SVA = Special visceral afferent carrying taste perception from the anterior 2/3rds of the tongue
GVE = General visceral efferent secretomotor of the submandibular and sublingual glands
Via submandibular ganglion
= Saliva production
Greater petrosal nerve carries GVE
Exits the petrous portion of the temporal bone where parasympathetic axons synapse in the pterygopalatine ganglion.
GVE = General visceral efferent
Secretomotor to lacrimal gland of eye (tear production)

Question 24

The primary gustatory region of the cortex is found where?

Answer 24

the insula

Question 25

What are the extracranial branches of CN VII?

Answer 25

BE/SVE Modality = Voluntary motor control to muscles of facial expression 5 branches: Temporal Zygomatic Buccal Mandibular Cervical GSA Modality = GAS to skin behind the ear Posterior auricular branch

Question 26

What attaches to the stapes and helps to dampen sounds (i.e. protects from intense/loud sounds and dampens endogenous sounds such as chewing, talking, and swallowing)? CN VII

Answer 26

the stapedius (SVE component)

Question 27

What condition results from trauma to the facial nerve, such as a viral meningitisinfection. With symptoms including: 1.) Weakness, twitching, or paralysis of facial muscles, including drooping of the eyelid and corner of the mouth. Damage to what portion of the facial nerve would these symptoms result from? 2.) Dry eye or mouth. Damage to what portion of the facial nerve would these symptoms result from? 3.) Impairment of taste. Damage to what portion of the facial nerve would these symptoms result from?

Answer 27

Bell's Palsy SVE portion GVE component SVA component

Question 28

Corneal reflex does what? Motor arc? Sensory arc? Desired response? Test? Clinical significance?

Answer 28

Corneal Reflex = protects eyes from foreign bodies Sensory arc: CN V1 (touch to surface of cornea) Motor arc: CN VII (orbicularis oculi) Desired response = BILATERAL regardless of input side! TEST: Cotton gauze touched to cornea of R eye should result in blink/closure of BOTH eyes Clinical significance? Cotton gauze touched to L eye, only R eye blinks  means sensory signal worked, but L motor did not work Cotton gauze touched to L eye, and no eyes blink  means sensory input did not work

Question 29

Review slide 39 chart

Question 30

What is the pathway for CN VIII = vestibulocochlear Nerve

Answer 30

Two separate nerves that travel together Pathway: Begins at base of pons and exits cranium via internal acoustic meatus. Terminates as separate nerves in inner ear Foramina: Internal Acoustic Meatus Function: Special Somatic Afferent (SSA) for two senses: Hearing (Cochlear) Balance & equilibrium (Vestibular)

Question 31

What is the pathway for CN IX = Glossopharyngeal Nerve?

Answer 31

Pathway: Nerve emerges from the brainstem in the lateral medulla and exits the posterior cranial fossa through the jugular foramen. Majority of nerve remains extracranial to innervate structures of face and throat Foramina: Jugular foramen Function: Glossopharyngeal has five (5) modalities BE/SVE – voluntary motor SVA – special visceral afferent GVE – general visceral efferent GVA – general visceral afferent GSA – general somatic afferent

Question 32

What are the fiber types of the glossopharyngeal nerve (CN IX)?

Answer 32

BE/SVE axons innervate stylopharyngeus (swallowing muscle) SVA axons carry taste perception from the posterior 1/3 of the tongue GVE axons innervate the parotid gland via otic ganglion (secretomotor function) GVA axons from the carotid body (visceral sensation from carotid body for chemoreception – maintaining BP) GSA axons - sensory from skin posterior to the ear, posterior 1/3 of tongue, and the afferent part of the gag reflex

Question 33

Pathway for CN X - Vagus Nerve?

Answer 33

Pathway: Nerve emerges from the brainstem in the lateral medulla and exits the posterior cranial fossa through the jugular foramen. Foramina: Jugular foramen Function: Vagus nerve has five (5) modalities BE/SVE – voluntary motor SVA – special visceral afferent GVE – general visceral efferent GVA – general visceral afferent GSA – general somatic afferent

Question 34

What are the fiber types of the vagus nerve (CN X)?

Answer 34

(1) BE/SVE axons innervate the majority of the muscles of the pharynx, larynx and soft palate (moving food towards esophagus during swallowing) (2) GSA axons from skin posterior to ear, dura in posterior cranial fossa, mucous membranes of pharynx & larynx (3) GVA axons from thoracic & abdominal viscera & aortic body Chemoreceptors – blood content Baroreceptors – blood pressure (4) SVA axons (taste) from the root of tongue and epiglottis region (5) GVE axons (parasympathetic) to thoracic and abdominal viscera up to left colic flexure. Synapse is in or around target organ.

Question 35

Vagus Nerve injury

Answer 35

Recurrent Laryngeal Nerve branch: BE/SVE– Branchial efferent / Special Visceral Efferent Nerve supplies muscles of the larynx/voice box Travels posterior to thyroid Common causes of injury: Tumor or after surgical intervention of the thyroid Bronchial carcinoma Aortic arch aneurysm Patient presentation includes: Hoarse voice Vocal changes (dysphonia) Difficulty producing speech

Question 36

What reflex is initiated in response to stroking the back of the throat and is mediated by the vagus nerve?

Answer 36

The gag reflex Gag Reflex = helps prevent choking Sensory arc: CN IX (touch to base of throat) Motor arc: CN X (motor response of pharynx) Desired response = BILATERAL regardless of input side! TEST: Touch one side of the oropharynx should result in contraction of soft palate muscles of BOTH sides (sometimes this can be elicited by just asking patient to say “ahhhh”) Clinical significance? CN X motor problem = uvula will deviate to the intact side (away from side of injury) CN IX sensory problem = NO RESPONSE (soft palate muscles do not contract at all) Protective response that prevents oral contents from entering the throat except as part of normal swallowing

Question 37

What is the pathway for spinal accessory nerve CN XI?

Answer 37

Pathway: Nerve begins at medulla and exits cranium via jugular foramen Foramina: Jugular foramen Function: voluntary motor to Sternocleidomastoid and Trapezius muscles SCM – contralateral rotation of head Traps – shoulder “raises” General Somatic Efferent (GSE)

Question 38

What is the pathway of the hypoglossal nerve? (CN XII)

Answer 38

Pathway: Nerve begins at medulla and exits cranium via hypoglossal canal Foramina: Hypoglossal canal Function: voluntary motor to muscles of the tongue General Somatic Efferent (GSE)

Question 39

What is the exception to the usual bilateral innervation that the cortex sends?

Answer 39

genioglossus muscle (contralateral)

Question 40

Common injury of the hypoglossal nerve CN XII? How do you test for it?

Answer 40

Pathway: Nerve begins at medulla and exits cranium via hypoglossal canal Foramina: Hypoglossal canal Function: voluntary motor to muscles of the tongue General Somatic Efferent (GSE) Testing CN XII= “Stick out your tongue”