Muscle Origin



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SSN ANATOMY

Workshop 6: Head & Neck II

1. Muscles of Mastication (p. 607)





Muscle

Origin

Insertion

Action

Temporalis





Temporal bone

Parietal bone



Coronoid process

Elevates jaw

Retracts jaw



Masseter

Zygomatic arch

Mandibular angle

Elevates jaw

Lateral Pterygoid (Superior Head)

Sphenoid bone

Temporomandibular Disk

Draws articular disk forward


Lateral Pterygoid (Inferior Head)

Lateral Side of Lateral Pterygoid Plate

Mandibular neck

(bilaterally) Protracts jaw

(unilaterally) Abducts jaw (grinding)

Medial Pterygoid

Medial Side of Lateral Pterygoid Plate

Mandibular angle

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)



Bone

Foramen/Canal

What They Transmit

Posterior Wall


Pterygoid process of sphenoid bone


  1. Pterygoid (vidian) canal

  2. Foramen Rotundum

  3. Pterygovaginal canal

  1. Vidian nerve




  1. Maxillary nerve

  2. 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. Superior orbital fissure




  1. Posterior superior alveolar foramina

  1. Infraorbital artery and nerve

  2. CN III, IV, V1, VI, ophthalmic vein

  3. Posterior-Superior alveolar neurovascular bundles

Roof


Greater wing of sphenoid bone

None




Inferior Boundary

Maxillary process, palatine bone, pterygoid process of sphenoid bone

  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.


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