Wk 5 Theory - Oral Health Sciences

What are the 4 muscles of mastication?

• Masseter

• Temporalis

• Medial Pterygoid

• Lateral Pterygoid

Masseter - Origin:

Origin (2 heads):

• Superficial head - anterior 2/3 of the lower border of the zygomatic arch.

• Deep head - posterior 1/3 of the lower border of the zygomatic arch.

Masseter - Insertion:

Angle of the mandible

Masseter - Innervation:

Masseteric branch of the mandibular nerve, which is a branch of Cn V (trigeminal nerve).

Masseter - Actions:

• raises mandible

• helps protrude mandible (superficial fibres)

• helps retract mandible (deep fibres)

Temporalis - Origin:

• Immediately inferior to the superior temporal line on the parietal bone.

• Deep temporo-parietal fascia.

Temporalis - Insertion:

Apex and medial surface of coronoid process of the mandible.

Temporalis - Innervation:

Deep temporal branches of the mandibular nerve, which is a branch of Cn V (trigeminal nerve).

Temporalis - Actions:

• raises mandible.

• helps retract mandible (posterior fibres)

Medial Pterygoid - Origin:

• Deep head - Medial surface of the lateral pterygoid plate.

• Superficial head - pyramidal process of the palatine bone and the posterior aspect of the maxillary tuberosity.

Medial Pterygoid - Insertion:

Medial surface of the ramus and angle of the mandible.

Medial Pterygoid - Innervation:

Medial pterygoid branches of the mandibular nerve (Cn V3), which is a branch of trigeminal nerve.

Medial pterygoid - Actions:

• raises mandible.

• helps protrude mandible

• unilateral contraction pulls the mandible into a lateral excursive movement.

Lateral Pterygoid - Origin:

• Superior head - infratemporal surface of the greater wing of the sphenoid.

• Inferior head - lateral surface of the lateral pterygoid plate.

Lateral Pterygoid - Insertion:

• Superior head - capsule of the TMJ.

• Inferior head - anterior aspect of the neck of the condyle.

Lateral Pterygoid - Innervation:

Lateral pterygoid branches of the mandibular nerve (Cn V3), which is a branch of trigeminal nerve.

Lateral Pterygoid - Actions:

• helps protrude mandible.

• unilateral contraction pulls the mandible into a lateral excursive movement (contralateral side).

• depresses the mandible and opens the mouth when assisted by the anterior belly of the digastric muscle and the mylohyoid muscle.

What are accessory muscles of mastication?

The muscles that assist the muscles of mastication.

List the accessory muscles of mastication.

Three main groups:

• Buccinator

• Suprahyoid Muscles:
  - Digastric
  - Mylohyoid
  - Geniohyoid
  - Stylohyoid

• Infrahyoid Muscles:
  - Omohyoid
  - Sternohyoid
  - Sternothyroid
  - Thyrohyoid

Buccinator - Origin:

•  Superior part - alveolar process of maxilla

• Inferior part - alveolar process of mandible

• Posterior part - pterygomandibular raphe.

Buccinator - Insertion:

Orbicularis oris (& other facial muscles).

Buccinator - Innervation:

Facial Nerve (Cn VII)

Buccinator - Actions:

• Compresses cheek

• Produces the action of sucking

Suprahyoid group:

• Act to elevate the hyoid or depress the mandible.

• If the mandible is fixed by the muscles of mastication, then they raise the hyoid.

• If the hyoid is fixed by the infrahyoid group, then they depress the mandible.

• Muscles include:
  - Digastric.
  - Geniohyoid.
  - Stylohyoid.
  - Mylohyoid.

Infrahyoid group:

• Act to fix the hyoid in order to depress the mandible

• Muscles include:
  - Sternohyoid
  - Omohyoid
  - Sternothyroid
  - Thyrohyoid

Digastric - Origin:

• Posterior belly - mastoid notch of the temporal bone.

• Anterior belly - digastric fossa located on the medial surface of the anterior portion of the mandible.

Digastric - Insertion:

• Body of the hyoid bone

• Creates a fibrous sling between the two bellies

Digastric - Innervation:

• Posterior belly - facial nerve Cn VII

• Anterior belly - mylohyoid branch of Cn V3

Digastric - Action:

• multiple - assists with:

• swallowing

• chewing

• speech

Geniohyoid - Origin:

Genial tubercles on the anterior aspect of the medial surface of the mandible (see osteology lectures).

Geniohyoid - Insertion:

Superior aspect of the hyoid.

Geniohyoid - Innervation:

Anterior ramus of spinal nerve C1 (via hypoglossal nerve - Cn XII).

Mylohyoid - Origin:

Mylohyoid line on the medial surface of the mandible.

Mylohyoid - Insertion:

Mylohyoid raphe & body of the hyoid

Mylohyoid - Action:

Elevate the FoM and/or depress the mandible.

Mylohyoid - Innervation:

Nerve to mylohyoid (of IAN - Cn V3)