Muscles of Mastication
What muscles form the hyoid muscle sling?
-Tongue and jaw muscles approach from above and anteriorly -Muscles and ligament of the temporal bone approach from the posterior -Extrinsic muscles of the larynx from below
How can the innervation ratio of 1:936 be interpreted?
1 motor neuron: 936 muscle cells
Identify the muscles of mastication from a transverse cut of the skull.
1. masseter M. 2. temporalis M. 3. lateral pterygoid M. 4. medial pterygoid M. 5. longus capitis M. 6. inferior nasal concha
What is the innervation ratio of the masseter?
1:650
What is the innervation ratio of the temporalis?
1:936
Bite force has been recorded as high as _______.
4400 N
What is the masseter?
A rectangular muscle that runs from the zygomatic arch to the lateral aspect of the lower border of the ramus of the mandible
What is the major action of the temporalis?
Elevate the mandible
What is the action of the geniohyoid?
Elevates hyoid bone, Depresses mandible when hyoid is fixed
What is the action of the mylohyoid?
Elevates hyoid bone, supports and raises floor of mouth. Depresses mandible when hyoid is fixed
What is the main action of the medial pterygoid?
Elevates the mandible and brings the teeth together
What action results from the contraction of the temporalis?
Elevates the mandible and closes the jaw bringing the teeth together
Where is the insertion of the masseter?
Extends from the second molar to the angle of the mandible
T or F? The stylohyoid muscle has a role in mandibular movement.
False, only contributes to hyoid fixation
Which arch are the muscles of mastication derived from?
First branchial arch paraxial mesoderm
What is the prime protractor of the mandible?
Inferior lateral pterygoid
What is the origin of the geniohyoid?
Inferior mental spine on posterior surface of mandible near the midpoint
What muscles stabilize or "fix" the hyoid bone in position?
Infrahyoid muscles
Where does the smaller superior head originate?
Infratemporal surface of the greater wing of the sphenoid
Where is the origin of the deep head of the masseter?
Inner surface of the zygomatic arch
Where is the origin of the deep head?
Inner surface of the zygomatic arch
Where does the smaller superior head of the lateral pterygoid insert?
Inserts on the articular disc, the joint capsule, and the neck of the condyle
Where does the temporalis insert?
Inserts on the coronoid process and anterior border of the ascending ramus
What is the temporalis?
Large fan shaped muscle with its origin on the inferior temporal line and the temporal fossa
What muscle is active during the power stroke?
Lateral pterygoid
Where does the anterior belly of the suprahyoid originate?
Lingual surface of the mandible close to the midline and becomes tendinous as it passes through a fibrous loop that is attached to the hyoid bone.
What is trismus?
Lockjaw
Where is the origin of the superficial head of the masseter?
Lower border of the zygomatic arch
What are the four pairs of primary muscles of mastication?
Masseter Temporalis Medial Pterygoid Lateral Pterygoid
What is the insertion of the mylohyoid?
Midline raphe, superior border of body of hyoid bone
What innervates the muscles of mastication?
Motor branch of the trigeminal nerve
What is lateral excursion?
Movement of the jaw away from the midline
What is the medial peterygoid?
Muscle that runs from the pterygoid fossa and medial surface of lateral pterygoid plate to the medial surface of the angle of the mandible
What are synergists?
Muscles that contract at the same time as the prime mover
What are the antagonist muscles?
Muscles that oppose the movement of primary mover muscle
What muscles make up the suprahyoid muscles?
Mylohyoid Digastrics Geniohyoids Stylohyoids
What is the origin of the mylohyoid?
Mylohyoid line on internal aspect of mandible
Middle fibers of the temporalis run ________.
Obliquely forward
Where does the larger inferior head of the lateral pterygoid originate?
On the lateral surface of the lateral pterygoid plate
Where does the inferior head of the lateral pteryoid insert?
On the pterygoid fovea on the anterior aspect of the condylar neck
What is a motor unit?
One motor neuron and all the skeletal muscle fibers that it innervates
What muscles make up the infrahyoids?
Sternothyroids Omohyoids Sternothyroids Thyrohyoids
What are the two heads of the masseter?
Superficial head and deep head
What are the two heads of the lateral pterygoid?
Superior and inferior
What is the insertion of the geniohyoid?
Superior border of body of hyoid bone
What muscles act against the fixed hyoid to depress the mandible during mastication?
Suprahyoid muscles
What are the accessory muscles?
Suprahyoids and infrahyoids
What is the contralateral excursion?
The insertion of the lateral pterygoid is lateral to its origin, and thus the lateral pterygoid muscle acting singly moves the mandible to the opposite side
What is the origin of the muscle?
The point of attachment that does not move when the muscle contracts
What is the insertion of the muscle?
The point of attachment that moves when the muscle contracts
Where does the posterior belly originate and insert?
The posterior belly originates on mastoid notch and inserts on the common tendon
What is the agonist muscle?
The prime mover
T or F? Muscles with high innervation ratios are strong, but cannot perform fine movements easily.
True
T or F? The muscles of mastication are derived from the first branchial arch paraxial mesoderm.
True
Infrahyoids are all innervated by ______.
cervical plexus
Both lateral pterygoids contract to cause ________.
depression of the mandible
If the infrahyoid muscles are relaxed, then the suprahyoid muscles can ______ the hyoid bone and move it anteriorly during swallowing.
elevate
When the masseter contracts, the teeth come together as the mandible is ______.
elevated
Contraction of both bellies of the digastric produces jaw opening when the hyoid is _____.
fixed
Posterior fibers of the temporalis run ________.
horizontal
The superficial portion aids in protruding the ______.
mandible
Contraction of both bellies of the digastric produces hyoid elevation when the hyoid is ______.
not fixed
The geniohyoid and mylohyoid initiate the _______ of the jaw.
opening
The movement of the mandible is result of contraction of ________.
skeletal muscle
Because the insertion is lateral to the origin, a __________ contraction can cause a contralateral excursion of the mandible.
unilateral
Anterior fibers of the temporalis run ______.
vertically
