Lecture Masticatory muscles

§THE JAW MUSCLES
(MASTICATORY MUSCLES)

People’s Teacher
Prof. Hoàng Tử Hùng, DDS, PhD
E:
W: hoangtuhung.com


Introduction
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
of all jaw muscles except the geniohyoid muscle by hypoglossal nerve (XII cranial nerve)
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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)

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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
Superficial part involved in protrusion
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The medial pterygoid muscle

The elevator muscles
- The masseter
- The medial pterygoid
- The temporal

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

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The temporal muscle

The elevator muscles
- The masseter
- The medial pterygoid
- The temporal

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
Temporal muscle is the most sensitive
muscle with the occlusal interferences
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The lateral pterygoid muscle

Lateral pterygoid m.
Superior belly
Inferior belly

Medial
pterygiod m.

buccinator

The depressor muscles:
‒ The lateral pterygoid muscle
‒ The suprahyoid muscles
‒ The digastric muscle
‒ The mylohyoid muscle
‒ The geniohyoid muscle

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
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The digastric 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
of mouth, which is necessary for deglutition

The depressor muscles:
‒ The lateral pterygoid muscle
‒ The suprahyoid muscles
‒ The digastric muscle

‒ The mylohyoid muscle
‒ The geniohyoid muscle

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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 depressor muscles:
‒ The lateral pterygoid muscle
‒ The suprahyoid muscles
‒ The digastric muscle
‒ The mylohyoid muscle
‒ The geniohyoid muscle

The geniohyoid muscle
Origin: inferior genial tubercle
Insertion: body of hyoid
Action: contributes to mylohyoid muscle action
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