Head and Neck Musculature Overview

Innervation and Blood Supply of Masticatory Muscles

  • Nerve Supply: All muscles of mastication are innervated by the third branch of the fifth cranial nerve, known as the trigeminal nerve.
  • Blood Supply: Derived from the maxillary artery.

Muscles of Mastication

  • Masseter Muscle:
    • Function: Most powerful muscle of mastication; elevates the mandible to close the mouth.
    • Origin: Zygomatic arch.
    • Insertion: Angle of the mandible.
  • Temporalis Muscle:
    • Function: Elevates the mandible when all fibers contract; posterior fibers contract to retrude (pull back) the mandible.
    • Origin: Temporal fossa.
  • Medial Tyrevoid Muscle:
    • Function: Acts as a weaker elevator of the mandible.
    • Origin: Medial side of the lateral pterygoid plate and the maxillary tuberosity.
    • Insertion: Medial side of the angle of the mandible.
  • Lateral Tyroid Muscle:
    • Function: Depresses (opens) and protrudes the mandible.
    • Origin: Greater wing of the sphenoid bone and the inferior part of the lateral side of the lateral pterygoid plate.

Suprahyoid Muscles

  • General Function: Strongly depress the mandible (open the mouth) and elevate the hyoid bone.
  • Digastric Muscle:
    • Function: Retrudes the mandible and lifts the hyoid bone to assist in pulling the mandible down.
    • Origin: Digastric notch of the temporal bone.
    • Insertion: Digastric fossa on the inferior surface of the mandible at the midsection.
    • Innervation: Primarily the trigeminal nerve, with additional supply from the facial nerve.
  • Myelophyoid Muscle:
    • Function: Forms the floor of the mouth; depresses the mandible while elevating the hyoid bone.
    • Origin: Medial surface of each side of the mandible.
    • Insertion: Hyoid bone.
  • Genial Pyruvate Muscle:
    • Function: Depresses the mandible.
    • Origin: Inferior genial tubercles.
    • Insertion: Hyoid bone.
  • Stylohyoid Muscle:
    • Function: Pulls the hyoid bone up and back, assisting in mouth closure and slight mandible retrusion.
    • Origin: Styloid process.
    • Insertion: Hyoid bone.

Infrahyoid Muscles and Neck Anatomy

  • Principle of Muscular Balance: Utilizes antagonistic pairing, where opposing muscles counteract primary actions to restore positional balance.
  • Omepoietoid Muscle:
    • Function: Depresses the hyoid bone.
    • Structure: Separated into two bellies by a tendon.
    • Origin: Upper border of the scapula.
    • Insertion: Sternocleidomastoid muscle (via a tendon) and the inferior part of the hyoid bone.
  • External Hyoid Muscle: Pulls the hyoid bone down.
  • Sternothyroid Muscle:
    • Function: Pulls the larynx down.
    • Origin: Upper part of the sternum.
    • Insertion: Thyroid cartilage of the larynx.
  • Thyrothyroid Muscle:
    • Function: Lifts the thyroid cartilage, raises the larynx, and depresses the hyoid bone.
    • Origin: Lateral side of the thyroid cartilage.
    • Insertion: Hyoid bone.
  • Sternocleidomastoid Muscle (SCM):
    • Function: Principal muscle of the neck used to turn the head.
    • Clinical Relevance: Flanked by anterior and posterior chains of lymph nodes; common source of referred pain to the temporalis muscle and occipital region.