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SSN Anatomy #6 - KEY
March 5, 2003
Brett Shore (bis2002) and Abigail Pease (arp2002)
1. Muscles of Mastication (p. 607)
Muscle
Temporalis
Masseter
Lateral
Pterygoid
(Superior
Head)
Lateral
Pterygoid
(Inferior Head)
Medial
Pterygoid
Origin
Temporal bone
Parietal bone
Zygomatic
arch
Sphenoid bone
Insertion
Coronoid process
Action
Elevates jaw
Retracts jaw
Elevates jaw
Mandibular angle
Temporomandibular Disk
Draws articular disk
forward
Lateral Side of
Lateral
Pterygoid Plate
Mandibular neck
Medial Side of
Lateral
Pterygoid Plate
Mandibular angle
(bilaterally) Protracts
jaw
(unilaterally)
Abducts jaw
(grinding)
Elevates jaw
2. What other muscles are innervated by the same cranial nerve as the muscles of
mastication (and which nerve)?
(CN V3)
Anterior belly of digastric (accessory muscle of mastication)
Mylohyoid (accessory muscle of mastication)
Tensor Tympani (dampens noise during mastication)
Tensor Veli Palatini (nothing to do with mastication but innervated by V3 anyway)
3. To help buy expensive medical textbooks you have decided to start babysitting. The
two little monsters you are watching tonight have come up with a new game. Cindy
sticks her finger in Mindy’s ear and Mindy gags. Mindy sticks her finger in Cindy’s ear
and Cindy coughs. After sending them both to bed, you grab your anatomy book to see
what’s going on. (April 643).
Gag reflex – mediated by CNIX (also has branch – tympanic nerve of Jacobson – that
innervates tympanic membrane and presumably, at least according to April, the signals
can get mixed up).
Cough reflex – mediated by CNX (also has branch –auricular branch – that innervates
external auditory meatus)
4. Pterygopalatine fossa (April, 603)
Posterior Wall
Bone
Pterygoid process
of sphenoid bone
Foramen/Canal
1. Pterygoid
(vidian) canal
2. Foramen
Rotundum
3. Pterygovaginal
canal
What They Transmit
1. Vidian nerve
2. Maxillary nerve
3. Pharyngeal Br.
of maxillary
artery
Medial Wall
Perpendicular
plate of the
palatine bone
1. Sphenopalatine
foramen
1. Sphenopalatine
neurovascular
bundle
Anterior Wall
Posterior surface
of the maxilla
1. Inferior orbital
fissure
1. Infraorbital
artery and
nerve
2. CN III, IV, V1,
VI, ophthalmic
vein
3. PosteriorSuperior
alveolar
neurovascular
bundles
2. Superior orbital
fissure
Roof
Inferior
Boundary
Greater wing of
sphenoid bone
Maxillary process,
palatine bone,
pterygoid process
of sphenoid bone
3. Posterior
superior
alveolar
foramina
None
1. Palatine canal
1. Palatine
neurovascular
bundle
5. Trace the pathway that mediates parotid gland salivation (April, 598).
Reference p. 598.
6. While on selective in the ER, your preceptor takes off early for the day and tells you to
hold down the fort. A patient comes in with the right side of his face expressionless and
drooping and with a steady stream of drool pouring out of the right corner of his mouth.
He complains of difficulty chewing his food. You also notice what you think are several
corneal abrasions. What nerve has been injured and how can you localize the site of the
lesion? (April, 613)
The patient has Bell’s palsy (facial nerve paralysis). If the lesion is at the stylomastoid
foramen, the nerve to the stapedius muscle and chorda tympani will be spared. If the
lesion is due to inflammation of the nerve within the facial canal (most common cause),
involvement of these nerves leads to hyperacusis and loss of taste over the anterior 2/3
of the tongue. An acoustic neuroma or fracture can produce a lesion in the internal
auditory meatus. The consequent involvement of the greater superficial petrosal nerve
(emerging from the facial nerve at the external genu just before it enters the facial canal)
would cause a loss of lacrimation and nasal gland secretion in addition to the above
symptoms.
[Also ask the students what other symptoms might result from an acoustic neuroma?]
Hearing and balance dysfunction because the vestibulocochlear nerve also traverses the
internal acoustic meatus.
7. Why is the maxillary sinus particularly prone to infection?
It doesn’t drain when patients are standing erect.
8. Name the branches of the external carotid artery in order of emergence from inferior
to superior.
Some People Like Fuzzy navels. Others Prefer MudSlides.
Superior Thyroid
Ascending Pharyngeal
Lingual
Facial
Occipital
Posterior auricular
Maxillary
Superficial temporal (continuation of external carotid superior to maxillary a.)
Nerve Quickies
9. What branch of what cranial nerve mediates the sneeze reflex?
Anterior superior alveolar branch of the maxillary division of CN V2, which conveys
general sensation from the nasal vestibule
10. What is the test for a lesion of CN XII?
Ask the patient to stick out his/her tongue. The tongue will deviate to the side of the
nerve with the lesion (b/c of unilateral paralysis of the genioglossus muscle, which
protracts the tongue).
11. All of the “glossus” muscles are innervated by the hypoglossal nerve (CN XII) except
________, which is innervated by ________ ?
Palatoglossus muscle. Pharyngeal branch of the vagus.
12. All of the “hyoid” muscles are innervated by branches of the ansa cervicalis except
_________ and __________, which are innervated by _________ and __________,
respectively. The only other muscle (one without hyoid in its name) innervated by the
ansa cervicalis is __________, another strap muscle.
The mylo-“hyoid” is innervated by the Mandibular nerve (remember it’s an accessory
muscle of mastication).
The stylo-“hyoid” is innervated by the Facial nerve. (Remember the facial nerve exits
the skull at the stylomastoid foramen right next to the origins of the stylohyoid and the
post. belly of the digastric and gives off branches to both.)
The sternothyroid, like all the infrahyoid (strap) muscles, is innervated by the inferior
ramus of the ansa.
13. All the muscles of the pharynx are innervated by the Vagus (CN X) except
________, which is innervated by ____________.
The stylopharyngeus is innervated by the glossopharyngeal nerve.
14. What physical finding is characteristic of a unilateral CN X lesion? What is the most
obvious consequence of a bilateral lesion?
Uvular deviation to the unaffected side and drooping of the soft palate on the affected
side (b/c of paralysis of the levator veli palatini and the intrinsic muscles of the soft
palate). Bilateral paralysis of laryngeal muscles causes aphonia (loss of voice) due to
paralysis of all laryngeal muscles.
15. What’s the only muscle associated with the soft palate not innervated by CN X?
The tensor veli palatini is innervated by the Mandibular nerve.
16. Anterior Cervical Triangle
A. Submental triangle
B. Submandibular triangle
C. Carotid triangle
D. Muscular triangle
A+B+C+D. Anterior Cervical triangle
E. Clavicle
F. Sternum (manubrium)
1a. Sternocleidomastoid muscle (clavicular head)
1b. Sternocleidomastoid muscle (sternal head)
2. Digastric muscle (anterior belly)
3. Digastric muscle (posterior belly)
4. Stylohyoid muscle
5. Thyrohyoid muscle
6. Omohyoid muscle (superior belly)
7. Sternohyoid muscle
8. Sternothyroid muscle