Muscles of Mastication (Quick info)

The muscles of mastication originate from the skull, span the TMJ, and insert into the mandible. On contraction, they act to move the mandible during movements of mastication.

The muscles of mastication are

  • Masseter
    • Superficial head
    • Deep head
  • Temporalis
  • Medial pterygoid
  • Lateral pterygoid
    • Superior head
    • Inferior head
Masseter Muscle:
  • It is a quadrilateral muscle that covers most of the lateral aspect of the ramus of the mandible
  • Lying superficial to the muscle is:
    • A portion of the parotid gland (facial process), the parotid duct
    • The transverse facial artery
    • The various branches of the facial nerve
  • The muscle is clearly divided into a superficial and a deep portion, which blend as a single anterior border
  • Origin:
    • The superficial portion arises as a thick tendon from the zygomatic process of the maxilla and as a fleshly fibers from the inferior border of the anterior two thirds of the zygomatic arch
    • The deep portion arises from the inner aspect of the zygomatic arch and the inferior border of posterior third of the zygomatic arch
  • Insertion:
    • The superficial fibers sweep inferiorly and posteriorly to insert into the angle of the mandible and the lower portion of the lateral aspect of the ramus.
      They cover the deep portion.
    • The deep fibers pass vertically downward to insert into the upper portion of the lateral aspect of the ramus.
      They DO NOT insert into the mandibular condyle, neck, nor the upper portion of the coronoid process.
  • Actions:
    • Elevation (Bilateral): the masseter muscle is a powerful elevator of the mandible and is very active during forceful (clenched) centric occlusion.
    • Ipsilateral excursion (Unilateral): The origin of the masseter muscle is slightly lateral to its insertion and therefore, a single masseter muscle can move the mandible to the same side.
    • Retrusion (Bilateral): when the mandible is in a protruded position, the deep fibers are in a position to help retrude the mandible.
    • SO in this case: the superficial head is responsible for:
      • Elevation (Bilateral)
      • Protrusion (Bilateral)
      • Ipsilateral excursion (Unilateral)
    • The deep head is responsible for:
      • Retrusion (Bilateral)
  • Blood Supply:
    • Maxillary artery (Masseteric branch)
    • Superficial temporal artery
    • Facial artery
  • Nerve Supply:
    • Anterior division of mandibular nerve of Trigeminal nerve (V Cranial nerve)
  • Examination:
    • By intraoral-extraoral compression between index finger and thumb.
    • Palpate the masseter bi-manually by placing a finger of one hand intraorally and the index and middle finger of the other hand on the cheek over the masseter over the lower mandibular ramus.
    • Look for facial symmetry, for evidence of enlarged masseter muscle (Masseteric hypertrophy) suggestive of clenching or bruxism.
Temporalis Muscle
  • To see the full extent of the temporalis muscle, it is necessary to remove the zygomatic arch.
  • It is fan shaped, with the periphery of the fan attached to the side of the skull and the handle of the fan attached to the coronoid process of the mandible.
  • The muscle is covered by a strong membranous sheet of fascia, which attaches superiorly to the superior temporal line. Below, the fascia splits to attach to the medial and lateral aspects of the zygomatic arch. Lying within the split portion above the arch is a variable amount of fat, some small vessels, and nerves.
  • Origin: The temporalis muscle originates as a fleshy fibers from
    • the curvilinear lower temporal line
    • the temporal fossa below the temporal line
    • the overlying temporal fascia.
  • Insertion: The fibers, arranged as  a fan, can be divided on the basis of function into vertical anterior, and middle vertical fibers and almost horizontal posterior fibers.
    • The anterior, middle, and posterior fibers converge and pass downward deep to the zygomatic arch as a thick tendon, to insert into the medial aspect of the coronoid process and the anteromedial border of the ramus of the mandible
  • Actions:
    • Resting Tonus (Bilateral): The temporalis muscle maintains normal mandibular rest position when the subject is in the upright position.
    • Elevation (Bilateral): The fibers of temporalis are active during end to end and centric occlusal biting positions; the muscle is most active, however, in centric occlusion.
    • Retrusion (Bilateral): The posterior fibers of temporalis lie in an almost horizontal plane and, therefore, are in a good position to pull the protruded mandible back to a centric position.
    • Ipsilateral excursion (Unilateral): the insertion of temporalis is medial to the origin, and therefore the temporalis muscle acting singly is capable of pulling the mandible to the same or ipsilateral side.
  • Blood Supply:
    • Second part of maxillary artery
    • Superficial temporal artery
  • Nerve Supply:
    • Anterior division of mandibular nerve of Trigeminal nerve (V Cranial nerve).
  • Examination:
    • By direct palpation of the temporal region.
    • Palpate the temporal origin of the temporalis muscle by asking the patient to clench their teeth.
    • Palpate the insertion of the temporalis tendon intraorally along the anterior border of the ascending mandibular ramus.
SEE ALSO
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