Muscles of Mastication Flashcards
Temporal fossa
Area inferior to temporal lines as far as the zygomatic arch
Infratemporal fossa
Area just below the zygomatic arch and medial to the ramus of the mandible
Depression of the mandible
Lowering the mandible, opening the oral cavity. This is due to bilateral muscle contraction
Elevation of the mandible
Bringing the mandible superior from an inferior position. This is due to bilateral muscle contraction.
Protrusion of the mandible
Bringing the mandible forward, like a bulldog (underbite) - due to bilateral muscle contraction
Retrusion of the mandible
Bringing the mandible posteriorly, this is due to bilateral muscle contraction
What is the unilateral movement of the mandible?
Lateral excursions - swinging the mandible right or left.
What muscles influence mastication, although they are not technically muscles of mastication?
Syprahyoid muscles and infrahyoid muscles, also the posterior neck musculature
How do the suprahyoid muscles influence the muscles of mastication?
They cannot move the mandible by themselves, they are synergists, but they also move when the mandible moves
How do the infrahyoid muscles influence the muscles of mastication?
The infrahyoid, or strap muscles, cannot move the mandible themselves by will influence how it moves because they are a counterforce to the suprahyoid muscles - they will function in stabilization of the mandible
How many muscles make up the muscles of mastication?
8 total, or 4 pairs of muscles
Where do the muscles of mastication originate?
The base of the skull
Where do the muscles of mastication insert?
the ramus of the mandible
What is the nerve innervation of the muscles of mastication?
All of the muscles of mastication are innervated by branches of the mandibular division of the trigeminal nerve (V3)
What provides the blood supply to the muscles of mastication?
Branches of the maxillary artery, which will correspond to the name of the muscle that they are supplying
In what plane(s) are the muscle fibers of the muscles of mastication oriented?
All of the muscles of mastication have fibers that run in 3 planes
anterior to posterior
superior to inferior
lateral to medial
What is the origin of the masseter?
Superficial head originates from the lower border of the anterior 2/3 of the zygomatic arch
Deep head originates from the medial surface and lower border of the posterior 1/3 of the zygomatic arch
What is the insertion of the masseter?
Lateral aspect of the ramus and angle of the mandible
What is the MAIN action of the masseter, and what are its supporting actions?
Main action = elevator of the mandible due to its prominent fibers being oriented superior to inferior
Supporting actions = protrusion with the fibers oriented anterior to posterior, and lateral excursions to the ipsilateral side by way of the fibers oriented medial to lateral
The masseter is said to be a prominent _____________ muscle
Grinding - masseter is very big in people who grind their teeth
What is the origin of the temporalis muscle?
The entire temporal fossa that is inferior to the temporal line
What is the insertion of the temporalis?
Coronoid process of the mandible, and the temporal crest primarily on the medial surface (insertion can go all the way down to the 3rd molar region)
Long, broad insertion to the ramus; therefore it has a lot of control over the mandible
What innervates the temporalis?
Anterior and posterior deep temporal nerves
What supplies the temporalis?
Anterior and posterior deep temporal arteries
What is the PRIMARY action of the temporalis?
Acts as an elevator of the mandible by way of the fibers that are oriented superior to inferior
What is the ONLY muscle that can retrude the mandible?
The temporalis (posterior fibers ONLY!)
What are the supporting actions of the temporalis muscle?
Lateral movement by pulling mandible to the ipsilateral (same) side
Retrusion by the posterior fibers only
It is also a postural muscle - the temporalis maintains the mandible in the rest position
What is the origin of the medial pterygoid?
The medial surface of the lateral pterygoid plate
And the superficial head of the medial pterygoid comes from the maxillary tuberosity
Where does the medial pterygoid insert?
Medial surface of the ramus of the mandible (pterygoid tubercle)
This is a broad attachment - it is basically the whole surface below the mandibular foramen
What is the primary action of the medial pterygoid?
Primary action is elevation because the primary fibers are oriented superior to inferior
What are the supporting actions of the medial pterygoid?
Protrusion (bringing mandible forward) and lateral movement to the CONTRALATERAL side
Which head of the lateral pterygoid is larger?
The inferior head
What is the origin of the inferior head of the lateral pterygoid?
Lateral surface of the lateral pterygoid plate
What is the insertion of the inferior head of the lateral pterygoid?
Pterygoid fossa - anterior and medial surface of the neck of the mandible
What is the origin of the superior head of the lateral pterygoid?
Infratemporal surface of the sphenoid bone - flat part of the sphenoid bone, lateral to the pterygoid process
What is the insertion of the superior head of the lateral pterygoid?
The pterygoid fossa, and the TMJ joint capsule and articular disc
What is the primary action of the lateral pterygoid?
Depression of the mandible because the primary fibers are oriented in an anterior to posterior direction
What are the supporting actions of the lateral pterygoid?
Protrusion, lateral movement to the contralateral side, and the superior head will be active during closure to brace the condyle against the eminence for smooth retrograde translation of the joint
What is the primary protruder of the mandible?
The lateral pterygoid
Does the lateral pterygoid independently move the disc of the TMJ?
NO!
The lateral pterygoid helps to stabilize the joint but the two heads of the muscle cannot independently move the disc. The superior head of the lateral pterygoid is a CT attachment to the capsule of the TMJ, which is why it may seem like it can independently move the joint, but it CANNOT
What is the dense network of veins surrounding the lateral pterygoid?
Pterygoid plexus
What does the pterygoid plexus connect to directly?
The cavernous sinus - deep venous drainage of the face
What is the reason that the branches of the mandibular division of the trigeminal nerve are intimately involved with the lateral pterygoid?
The foramen ovale lies just medial to the lateral pterygoid, and the trigeminal nerve passes through the foramen ovale so the branches of the mandibular division of trigeminal are so close
What supplies the lateral pterygoid?
The maxillary artery, it may pass deep or superficial to the lateral pterygoid
What muscle is prone to spasms, and why?
The lateral pterygoid, because it does not contain muscle spindles. This is thought to be related to TMD
Masticator space
Fascial space enclosing the muscles of mastication and everything related to them
This fascia is continuous from temporalis around pterygoids up through all of masseter
What are the bilateral movements of muscle pairs that open and close the mandible?
protrusion
retrusion
elevation
depression
What is required in order to make lateral excursions of the mandible?
Unilateral contraction of muscles that pull the mandible to the desired side
What is the rotating condyle?
the condyle in the fossa
What is the orbiting condyle?
the condyle out of the fossa
Condyle on side to which movement is directed
rotating condyle
Condyle on opposite side, moves in an arc around the rotating condyle
orbiting condyle
If you move the mandible to the right, what muscles are contracting?
The right masseter and temporalis because they move to the ipsilateral (same) side and then then left medial and lateral pterygoids because they move to the contralateral side
