Muscles Of Mastication - Ch 4

Front 1

Masseter Muscle

Back 1

Most superficially and strongest muscle of mastication.

F - Via bilateral contration, to elevate the mandible, raising the lower jaw.

O - Superficial head originates from the (A) 2/3rd of the lower border of the zygomatic arch. Deep head originates from the (P) 1/3rd & the entire (M) surface of the zygomatic arch.

I - Superficial head inserts on the (L) surface of the angle on the mandible and the deep head inserts on the ramus superior to the angle.

N - 5th Cranial or Trigeminal Nerve

Front 2

Temporalis Muscle

Back 2

Fan shaped muscle on each side of the head that fills the temporal fossa.

I - Inserts on the coronoid process of the mandible

N - 5th cranial or trigeminal nerve
F - Elevate the mandible by raising the lower jaw and also moving the lawer jaw backwards.

O - From the entire temporal fossa that is bound at the top by the inferior temporal line and at the bottom by the infratemporal crest

Front 3

Medial Pterygoid Muscle

Back 3

AKA internal pterygoid muscle. Deep to the masseter muscle and weaker than the masseter muscle.

F - Elevates the mandible, raising the lower jaw.

O - From the pterygoid fossa on the medial surface of the lateral pterygoid plate of the sphenoid bone.

I - The medial surface of the angle of the mandible.

N - 5th cranial or trigeminal nerve.

Front 4

Lateral Pterygoid Muscle

Back 4

Muscle lies within the infratemporal fossa, deep to the tempralis muscle.

F - Tendency to depress the mandible, lowering or opening of the jaw. When both muscles contract, the jaw is moved forward. Movement of just on muscle causes the jaw to shift to the opposite side causing jaw to move laterally.

O - Superior head originates from the (I) surface of the greater wing of the sphenoid bone. The inferior head originates from the (L) surface pterygoid plate of the sphenoid bone.

I - Both insert of the anterior surface of the neck of the mandibular condyle at the ptergoid fovea.

N - 5th cranial or trigeminal nerve.

Front 5

Hyoid Muscle

Back 5

Superficial position of the neck tissues. Can be grouped by suprahyoid or infrahyoid muscles.

Assist in the actions of mastication and swallowing.

Both groups are some way attached to the hyoid bone, which is a bone suspended inferior to the mandible.

Front 6

Suprahyoid Muscles

Back 6

Located superior to the hyoid bone and then further divided by their anterior posterior positions.

Front 7

Anterior Suprahyoid Muscle Group

Back 7

Includes the anterior belly of the diagastric, mylohyoid, and geniohyoid muscles.

F - Cause the elevation of the hyoid bone and larynix, if the mandible is stabilized by contraction of the muscles. (Occurs during swallowing)

F - Causes mandible to depress and the jaws to open.

Front 8

Posterior Suprahyoid Muscle Group

Back 8

Includes the posterior belly of the digastric and stylohyoid muscles

F - Cause the elevation of the hyoid bone and larynix, if the mandible is stabilized by contraction of the muscles. (Occurs during swallowing)

Front 9

Digastric Muscle

Back 9

Suprahyoid muscle that has two seperate bellies, the anterior and posterior bellies

F - Demarcates the superior portion of the anterior cervical triangle on each side of the neck.

O - Anterior belly originates on a tendon loosely attached to the body and greater cornu of the hyoid bone called the intermediate tendon. Posterior belly arises from the mastoid notch.

I - Anterior belly inserts close to the symphysis on the inner surface of the mandible. Posterior belly inserts on the intermediate tendon.

N - Anterior belly innervated by the mylohyoid nerve (a branch of the 5th cranial canal or trigeminal nerve). The posterior belly is innervated by the posterior digastric nerve (a branch of the 7th cranial or facial nerve)

Front 10

Mylohyoid Muscle

Back 10

Anterior suprahyoid muscle that is deep to the digastric muscle, with fibers running transversly between the two sides of the mandible.

F - Elevates the hyoid bone, depresses the mandible, forms the floor of the mouth, and helps elevate the tongue.

O - From the mylohyoid line on the inner surface of the mandible.

I - On the body of the hyoid bone.

N - Innervated by the mylohyoid nerve (a branch of the 5th cranial or trigeminal nerve)

Front 11

Stylohyoid Muscle

Back 11

Thin posterior suprahyoid muscle, anterior and superficial to the posterior belly of the digastric muscle

O - Syloid process of the temporal bone

I - Body of the hyoid bone

N - Innervated by the stylohyoid nerve ( a branch of the 7th cranial or facial nerve)

Front 12

Geniohyoid Muscle

Back 12

Anterior suprahyoid muscle that is deep to the mylohyoid muscle.

O - From the meidal surface of the mandible and near the symphysis at the genial tubercles.

I - Body of the hyoid bone

N - Innervated by the 1st cranial nerve, conducted by way of the 12th cranial or hypoglossal nerve.

Front 13

Infrahyoid Muscles

Back 13

Four pairs of hyoid muscles inferior to the hyoid bone.

F - Depress the hyoid bone

N - All are innervated by the 2nd and 3rd cervical nerves.

Front 14

Sternothyroid Muscle

Back 14

Is an infrahyoid muscle located superficial to the thyroid gland.

F - Depresses the thyroid cartilage and larynx. (Does NOT directly depress the hyoid bone.)

O - From the posterior surface of the sternum, deep and medial to the sternohyoid muscle, at the level of the first rib.

I - On the thyroid cartilage

N - 2nd and 3rd cervical nerves

Front 15

Sternohyoid Muscle

Back 15

Infrahyoid muscle superficial to the sternothyroid muscle as well as the thyroid gland and cartilage.

O - From the posterior and superior surfaces of the sternum, close to where the sternum joins each clavicle.

I - Body of the hyoid bone

N - 2nd and 3rd cervical nerves

Front 16

Omohyoid Muscle

Back 16

Infrahyoid muscle lateral to both the sternothyroid and thyrohyoid muscles.
(Has a superior belly and an inferior belly)
-Superior belly divides the anterior cervical triangle into the carotid and muscular triangles.
- Inferior belly in the posterior cervical triangle serves to demarcate the subclavian triangle from the occipital triangle.

O - Inferior belly originates from the scapula. Superior belly originates from the short tendon attached to the inferior belly.

I - Inferior belly attaches to the SCM and is attached by a short tendon to the superior belly. Superior belly inserts on the lateral border of the body of the hyoid bone.

N - 2nd and 3rd cervical nerves.

Front 17

Thyrohyoid Muscle

Back 17

Is covered by the omohyoid and sternohyoid muscles.

F - Depresses the hyoid bone, and raises the thyroid cartilage and larynx.

N - 2nd and 3rd cervical nerves.

O - On the thyroid cartilage

I - On the body and greater cornu of the hyoid bone.