Muscles of Mastication

• The muscles of mastication are associated with:
  • Movements of the jaw:
    • Temporomandibular joint:
      • They are one of the major muscle groups in the head:
        • The other being the muscles of facial expression.
• The are four muscles of mastication are:
  • The masseter:
    • Composed of the superficial and deep head
  • The temporalis:
    • The sphenomandibularis:
      • Is considered a part of the temporalis by some sources, and a distinct muscle by others
  • The medial pterygoid
  • The lateral pterygoid
• The muscles of mastication develop:
  • From the first pharyngeal arch:
    • Thus, they are innervated by:
      • A branch of the trigeminal nerve (CN V):
        • The mandibular nerve
• The masseter muscle:
  • Is the most powerful muscle of mastication
  • It is quadrangular in shape
  • Can be split into two parts:
    • Deep and superficial
  • The entirety of the muscle:
    • Lies superficially to the pterygoids and temporalis:
      • Covering them
  • Attachments:
    • The superficial part:
      • Originates from maxillary process of the zygomatic bone
    • The deep part:
      • Originates from the zygomatic arch of the temporal bone
    • Both parts attach:
      • To the ramus of the mandible
  • Actions:
    • Elevates the mandible, closing the mouth
  • Innervation:
    • Mandibular nerve (V)

• The temporalis muscle:
  • Originates from the temporal fossa:
    • A shallow depression:
      • On the lateral aspect of the skull
  • The muscle is covered:
    • By tough fascia which can be harvested surgically and used to repair a perforated tympanic membrane:
      • An operation known as a myringoplasty
  • Attachments:
    • Originates from the temporal fossa
    • It condenses into a tendon:
      • Which inserts onto:
        • The coronoid process of the mandible
  • Actions:
    • Elevates the mandible, closing the mouth.
    • Also retracts the mandible:
      • Pulling the jaw posteriorly
  • Innervation:
    • Mandibular nerve (V)

• The medial pterygoid muscle:
  • Has a quadrangular shape
  • With two heads:
    • Deep and superficial
  • It is located:
    • Inferiorly to the lateral pterygoid
  • Attachments:
    • The superficial head:
      • Originates from:
        • The maxillary tuberosity and the pyramidal process of palatine bone
    • The deep head:
      • Originates from:
      • The medial aspect of the lateral pterygoid plate of the sphenoid bone
    • Both heads attach to:
      • The ramus of the mandible near the angle of mandible
  • Actions:
    • Elevates the mandible, closing the mouth.
  • Innervation:
    • Mandibular nerve (V)
• The lateral pterygoid muscle:
  • Has a triangular shape
  • With two heads:
    • Superior and inferior
  • It has horizontally orientated muscle fibres:
    • Thus is the major protractor of the mandible
  • Attachments:
    • The superior head:
      • Originates from:
        • The greater wing of the sphenoid bone
    • The inferior head:
      • Originates from:
        • The lateral pterygoid plate of the sphenoid bone
    • The two heads converge into a tendon:
      • Which attaches to the neck of the mandible
  • Actions:
    • Acting bilaterally:
      • The lateral pterygoids protract the mandible:
        • Pushing the jaw forwards
    • Unilateral action:
      • Produces the ‘side to side’ movement of the jaw
        • Note:
          • Contraction of the lateral pterygoid will produce lateral movement on the contralateral side:
            • For example, contraction of left lateral pterygoid will deviate the mandible to the right
  • Innervation:
    • Mandibular nerve (V)

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