Muscles Of Mastication

INTRODUCTION:
  • Mastication- four muscles of mastication (or musculi masticatorii) - adduction and lateral motion of the jaw.
  • Muscles associated hyoid also responsible for opening the jaw
  • Embryological origin from the first pharyngeal arch.
TYPES:
  • PRIMARY MUSCLES OF MASTICATION:
  1. Temporalis: fan shaped & fills the temporal fossa
  2. Masseter( quadrilateral): Covers lateral surface of ramus of Mandible & has 3 layers
  3. Lateral Pterygoid: Short, conical & has upper 7 lower head
  4. Medial pterygoid (quadrilateral):Has a small superficial & a large deep head
MUSCLE ORIGIN FIBERS INSERTION NERVE SUPPLY & NUCLEI ACTION
Masseter superficial layer:Ant. 2/3rd of lower border of zygomatic arch & zygomatic process of maxilla
Middle layer: Ant. 2/3rd of deep surface & post. 1/3rd of lower border of zygomatic arch
deep layer:Deep surface of zygomatic arch
superficial:down & back at 45o
Middle & deep:vertically down
3 layers seperated by an artery & a nerve
Superficial:Lower part of lateral surface of ramus
Middle: middle part of ramus
Deep:Upper part of ramus & coronoid process
Massetric nerve(C.N.V3 ant. div.)(mesencephalic nucleus and the motor nucleus of trigeminal nerve ) Elevtaes mandible to close mouth
Temporalis Temporal fossa excluding zygomatic boneTemporal fascia Converge & pass through gap deep to zygomatic arch Margins & deep surface of coronoid process
Ant. border of ramus
2 deep temporal branches(C.N.V3 ant. div.) Elevates mandible
Retracts Mandible
Side to side grinding movement
Lateral Pterygoid Upper Head:Infratemporal surface& greater wing of sphenoid
Lower Head:Lateral surface of lateral pterygoid plate
Back & Lateral & converge for insertion Upper head:Pterygoid fovea at neck of mandible
Lower head:Ant. margin of articular disc & TMJ capsule
Lateral pterygoid branch (Ant. div. of C.N.V3) Depress mandible
Protrude mandible
grinding movement
Medial Pterygoid Superficial Head: Tuberosity of maxilla & adjoining bone
Deep Head:Medial surface of lateral pterygoid plate& adjoining process of palatine bone
Down, back & laterally Roughened area on medial surface of angle & adjoinig ramus of mandible, below & behind madibular foramen & mylohyoid groove Nerve to Medial Pterygoid( Main trunk of C.N. V3) Elevates Mandible
Protude mandible
Grinding movement
  • SECONDARY MUSCLES OF MASTICATION:
  1. Suprahyoid muscles
  2. Digastric:Elevate hyoid , depress mandible
  3. Stylohyoid:draw the hyoid bone backwards and elevate the tongue.
  4. Mylohyoid:Raises oral cavity floor, elevates hyoid, elevates tongue, depresses mandible
  5. Geniohyoid:carry hyoid bone and the tongue upward during deglutition
  • Infrahyoid muscles
  1. Sternohyoid:Depress Hyoid bone
  2. Thyrohyoid:Elevates thyroid Depress Hyoid bone
  3. Omohyoid:Depresses the larynx and hyoid bone. Also carries hyoid bone backward and to the side
Exam Question
  • The muscles of mastication are temporalis, masseter, medial pterygoid, lateral pterygoid
  • Masseter originates from mesencephalic nucleus and the motor nucleus of trigeminal nerve
  • All primary muscles of mastication are supplied by mandibular nerve
  • Muscles that elevates mandible to close the mouth are temporalis, masseter & medial pterygoid
  • The only primary muscle that depress mandible to open mouth is lateral pterygoid
  • All Muscles of mastication are supplied by branches from Ant. div. of mandible Except Medial Pterygoid
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