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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