Lecture Masticatory muscles

Trang 1 §THE JAW MUSCLES MASTICATORY MUSCLESPeople’s Teacher Trang 2 Introduction1- the jaw muscles are muscles which arise from or insert in the mandible and which act to the movement

§THE JAW MUSCLES

(MASTICATORY MUSCLES)

People’s Teacher

Prof Hoàng Tử Hùng, DDS, PhD E: tuhung.hoang@gmail.com

1- the jaw muscles are muscles which arise from or insert in the mandible and which

act to the movement of the mandible

2- Any single action of the mandible is the product of the closely integrated and highly

coordinated performance of several jaw muscles 3- In a symmetrical movement the homologous muscles on either side are synergists

and antagonists in an asymmetrical movement

4- The simplified classification of mandibular movement is usually described as follow: elevation, depression, protrude, retrude, and lateral movement, however, the real

movements are complex patterns in which many of the single movement are combined 5- The branches of mandibular nerve (V-3 cranial nerve) control and regulate activities

The Jaw muscles consist of:

The elevator muscles:

‒ The (two) masseter muscle(s)

‒ The (two) medial (internal) pterygoid muscle(s)

‒ The (two) temporal muscle(s)

The depressor muscles:

‒ The (two) lateral pterygoid muscle(s)

‒ The suprahyoid muscles

‒ The (two) digastric muscle(s)

‒ The (two) mylohyoid muscle(s)

‒ The (two) geniohyoid muscle(s)

The masseter The elevator muscles

- The masseter

- The medial pterygoid

- The temporal

Origin:

- Superficial part: anterior two-thirds of zygomatic arch

- Deep part: interior surface of zygomatic arch

Insertion:

- Superficial part: mandibular angle

- Deep part: mandibular ramus

Action:

Elevates the mandible

The medial pterygoid muscle

Origin: pterygoid fossa and maxillary tuberosity

Insertion: medial aspect of mandibular angle and distal aspect of the ramus

Action:

Elevates the mandible and involved in lateral

movements

The elevator muscles

- The masseter

- The medial pterygoid

- The temporal

The temporal muscle

Origin: 3 portions

‒ Temporal portion: temporal fossa

‒ Fascial portion: temporal fascia

‒ Zygomatic portion: internal aspect of

zygomatic arch

Insertion: internal aspect of coronoid process

and anterior margin of the ramus

Action: elevates the mandible

anterior belly involve in protrusion) posterior belly retracts the mandible

The elevator muscles

- The masseter

- The medial pterygoid

- The temporal

The lateral pterygoid muscle

Lateral pterygoid m.

Superior belly

Inferior belly

Medial pterygiod m.

buccinator

Origin:

- Superior belly (Sb): lower surface of sphenoid

- Inferior belly (Ib): 3/4 inferior of lateral aspect of lateral lamina of pterygoid process

Insertion:

- Sb: anterior portion of the disc and capsule

- Ib: pterygoid fossa of the neck of the mandible

Action:

Sb contracts during retrusion and closing of mouth

Ib contracts in protrusion and opening of mouth

If only one side contracts: contralateral lateral movement WWW.HOANGTUHUNG.COM

The depressor muscles:

‒ The lateral pterygoid muscle

‒ The suprahyoid muscles

‒ The digastric muscle

‒ The mylohyoid muscle

‒ The geniohyoid muscle

Origin: mastoid notch (posterior belly)

Insertion: digastric fossa of mandible (anterior

belly)

An intermediate tendon is between the anterior

and the posterior belly that is attached by a

fascial looplike strip to the hyoid

Action:

- When the hyoid bone is fixed (by suprahyoid

and infrahyoid muscles): the mandible is

depressed and pulled backward

- When mandible is stabilized: digastric and other

suprahyoid elevate the hyoid bone and the floor

The digastric muscle

The depressor muscles:

‒ The lateral pterygoid muscle

‒ The suprahyoid muscles

‒ The digastric muscle

‒ The mylohyoid muscle

‒ The geniohyoid muscle

the mylohyoid muscle

Origin: mandibular mylohyoid line

Insertion: mylohyoid raphe and hyoid body

Action: depresses mandibular, elevates floor

of mouth and hyoid bone

Anatomically: forms the floor of the mouth,

separating it from suprahyoid region

The geniohyoid muscle

Origin: inferior genial tubercle

Insertion: body of hyoid

Action: contributes to mylohyoid muscle action

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The depressor muscles:

‒ The lateral pterygoid muscle

‒ The suprahyoid muscles

‒ The digastric muscle

‒ The mylohyoid muscle

‒ The geniohyoid muscle