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