Muscles

• Muscles of Head and Neck


  • Muscles of Mastication
  • Hyoid Muscles
  • Cervical muscles
  • Muscles of facial expression
  • Muscles of the tongue
  • Muscles of the pharynx
• Muscles of Mastication


  4 Pairs: Masseter, Temporalis, Medial Pterygoid, Lateral Pterygoid

  
• Origin

  Attached to the least movable structure
• Insertion


  Attached to the more movable structure
• Action


  The movement when the muscle fibers contract
• Muscles of Mastication


  • All originate on the Cranium
  • All insert into the mandible
• Actions of Muscles of Mastication

  • Depression
  • Elevation
  • Protrusion
  • Retraction
  • Lateral deviation

  
• Innervation of Muscles of Mastication

  V3 (Third division of the trigeminal)
• Masseter Muscle


  Has two heads: Superficial and Deep
• Masseter Muscle


  • Both heads originate from the zygomatic arch
  • Both heads insert on the external surface of the mandible
• Masseter Muscle Action


  Elevates the mandible, raising the lower jaw

  
• Masseter Muscle Innervation


  Innervated by the masseteric nerve, a branch of the mandibular nerve (V3)

  
• Temporalis Muscle


  Fan-shaped muscle
• Temporalis Muscle


  • Origin: Temporal fossa
  • Insertion: Coronoid process
• Temporalis Muscle Action

  • Elevates the mandible, raising the lower jaw
  • If only the posterior fibers contract, the muscle moves the lower jaw backward, causing retraction of the mandible

  
• Temporalis Muscle Innervation


  Innervated by the deep temporal nerve, a branch of the mandibular nerve (V3)
• Medial Pterygoid Muscle


  The deepest muscle of mastication, has two heads: superficial and deep
• Medial Pterygoid Muscle


  • Deep head origin: Medial surface of the lateral pterygoid plate of the sphenoid bone
  • Superficial head origin: Maxillary tuberosity
  • Both heads insert on the medial surface and angle of the mandible

  
• Pterygomandibular Space


  • Formed by the Lateral pterygoid muscle (roof), the Medial pterygoid muscle (medial wall), and the Mandibular ramus (lateral wall)
  • It is the injection site for the inferior alveolar block

  
• Medial Pterygoid Muscle Action

  Elevates the mandible, raising the lower jaw

  
• Medial Pterygoid Muscle Innervation

  Medial pterygoid nerve, a branch of V3

  
• Lateral Pterygoid Muscle


  Has two separate heads of origin: Superior and Inferior
• Lateral Pterygoid Muscle


  • Superior head origin: Greater wing of the sphenoid bone
  • Superior head insertion: Anterior surface of the neck of the mandibular condyle at the pterygoid fovea
  • Inferior head origin: Lateral surface of the lateral pterygoid plate of the sphenoid bone
  • Inferior head insertion: Anterior surface of the neck of the mandibular condyle at the pterygoid fovea

  
• Lateral Pterygoid Muscle Action

  • The only muscle of mastication that assists in depressing the mandible
  • When both muscles contract, the lower jaw moves forward causing the protrusion of the mandible
  • If only one muscle contracts, the lower jaw shifts to the contralateral side, causing lateral deviation of the mandible

  
• Lateral Pterygoid Muscle Innervation

  Lateral pterygoid nerve, a branch of the mandibular nerve V3

  
• Hyoid Bone

  Horseshoe-shaped bone suspended inferior to the mandible, does not articulate with any other bone

  
• Hyoid Muscle Groups


  • Suprahyoid Muscles: Mylohyoid, Geniohyoid, Stylohyoid, Digastric
  • Infrahyoid Muscles: Thyrohyoid, Omohyoid, Sternohyoid, Sternothyroid
• Hyoid Muscles


  • All attach to the hyoid bone, except the sternothyroid muscle

  
• Suprahyoid Muscles


  Muscles superior to the hyoid bone
• Suprahyoid Muscles Action

  • Elevation of the hyoid bone and larynx
  • Cause the mandible to depress and the jaws to open along with lateral pterygoids

  
• Digastric Muscle


  Has two separate bellies: anterior and posterior
• Digastric Muscle


  • Anterior belly origin: Digastric fossa on the medial surface of the mandible
  • Anterior belly insertion: Intermediate tendon which passes through a pulley attached to the hyoid bone
  • Posterior belly origin: Mastoid notch, medial to the mastoid process of the temporal bone
  • Posterior belly insertion: Intermediate tendon which passes through a pulley attached to the hyoid bone

  
• Digastric Muscle Action


  Elevates the hyoid bone or depresses the mandible
• Digastric Muscle Innervation


  • Anterior belly: mylohyoid nerve (V3)
  • Posterior belly: posterior digastric nerve (VII)

  
• Mylohyoid Muscle


  Deep to the digastric muscle, fibers run between the two mandibular rami

  
• Mylohyoid Muscle


  • Origin: Mylohyoid line on the medial surface of the mandible
  • Insertion: Right and left muscles unite medially at the mylohyoid raphe, forming the floor of the mouth
  • Most posterior fibers insert on the body of the hyoid bone

  
• Mylohyoid Muscle Action


  Elevates the hyoid bone, depresses the mandible, forms the floor of the mouth
• Mylohyoid Muscle Innervation


  Mylohyoid nerve (a branch of the IA which is a branch of V3)

  
• Stylohyoid Muscle


  • Origin: Styloid process
  • Insertion: Hyoid bone

  
• Stylohyoid Muscle Action


  Elevates the hyoid bone