Mastication Muscles

Anatomy

• Muscles Involved: Four main muscles responsible for mastication:

  1. Masseter: Thick muscle located in the jaw, essential for elevating the mandible.
  2. Temporalis: Fan-shaped muscle above the ears, aids in closing the jaw and retraction of the mandible.
  3. Medial Pterygoid: Located on the inner side of the mandible, assists in elevating and moving the mandible side-to-side.
  4. Lateral Pterygoid: Located anteriorly, responsible for the depression and protraction of the mandible.

• Innervation: All muscles of mastication are primarily innervated by the mandibular branch of the trigeminal nerve (CN V3).

• Blood Supply: Supplied by branches of the maxillary artery.

Physiology

• Jaw Movements: Muscles coordinate to produce complex movements:

  • Elevation (closing the jaw)
  • Depression (opening the jaw)
  • Protraction (moving forward)
  • Retraction (pulling backward)
  • Lateral movement (side-to-side grinding)

• Role in Chewing: They facilitate the grinding and cutting of food, breaking it down into smaller pieces for easier digestion.

Clinical Significance

• Temporomandibular Joint Disorders (TMD): Dysfunction or pain in the muscles and joints involved in mastication can lead to TMD, characterized by:

  • Jaw pain
  • Clicking or popping sounds
  • Difficulty in moving the jaw

• Bruxism: Involuntary teeth grinding can affect the muscles of mastication, leading to muscle hypertrophy and dental problems.

• Dental Health: Poor alignment or missing teeth can alter normal muscle function, negatively impacting chewing efficiency and overall oral health.

Function in Digestion

• Mechanical Breakdown: Muscles of mastication prepare food for enzymatic digestion by crushing and grinding it, increasing surface area.

• Food Mixing: Facilitate the mixing of food with saliva, which contains enzymes that begin the digestive process.

• Formation of Bolus: Assist in shaping chewed food into a bolus for effective swallowing, ensuring smooth passage to the esophagus.

• Stimulating Salivary Glands: The act of chewing stimulates salivary secretion, aiding in digestion and oral moisture.

Mastication Muscles

• Masseter, Temporalis, Medial Pterygoid, and Lateral Pterygoid are the four primary muscles involved in chewing.
• Masseter is a thick muscle located in the jaw, responsible for elevating the mandible (closing the jaw).
• Temporalis is a fan-shaped muscle above the ears, assisting in closing the jaw and retracting the mandible (pulling it backward).
• Medial Pterygoid is located on the inner side of the mandible, helping to elevate and move the mandible side-to-side.
• Lateral Pterygoid is situated anteriorly, responsible for depressing and protracting the mandible (opening and moving it forward).

Innervation and Blood Supply

• All mastication muscles are primarily innervated by the mandibular branch of the trigeminal nerve (CN V3).
• They are supplied by branches of the maxillary artery.

Jaw Movements

• The coordinated actions of these muscles produce complex jaw movements including:
  • Elevation: Closing the jaw.
  • Depression: Opening the jaw.
  • Protraction: Moving the jaw forward.
  • Retraction: Pulling the jaw backward.
  • Lateral movement: Side-to-side grinding.

Role in Chewing

• The mastication muscles facilitate the grinding and cutting of food, breaking it down into smaller pieces for easier digestion.

Clinical Significance

• Temporomandibular Joint Disorders (TMD) can occur due to dysfunction or pain in the muscles and joints involved in chewing.
  • Symptoms include jaw pain, clicking or popping sounds, and difficulty moving the jaw.
• Bruxism, involuntary teeth grinding, can affect the mastication muscles, potentially leading to muscle hypertrophy and dental problems.
• Dental health is impacted by proper alignment and the presence of all teeth. Malalignment or missing teeth can alter muscle function, negatively affecting chewing efficiency and oral health.

Function in Digestion

• The muscles of mastication play a vital role in the digestive process:
  • Mechanical breakdown: They crush and grind food, increasing surface area for enzymatic digestion.
  • Food mixing: They facilitate mixing food with saliva, which contains digestive enzymes.
  • Formation of bolus: They assist in shaping chewed food into a bolus for efficient swallowing, ensuring smooth passage to the esophagus.
  • Stimulating salivary glands: The act of chewing stimulates saliva production, aiding in digestion and maintaining oral moisture.

Muscles of Mastication

• Muscles of mastication attach to the mandible and allow for movement during chewing and grinding.
• These muscles allow the mandible to move in five ways:
  • Protrusion (forwards)
  • Retraction (backwards)
  • Elevation (up/close)
  • Depression (down/open)
  • Rotation (side-to-side)

Why are these muscles important?

• Knowledge of these muscles is vital for identifying and explaining conditions such as:
  • Pain during mastication
  • Trismus (difficulty opening the mouth)
  • Clenching and grinding

Masseter

• Consists of two parts: superficial and deep
• Superficial
  • Origin: anterior two-thirds of the lower border of the zygomatic arch
  • Insertion: outer surface of the ramus of the mandible
• Deep
  • Origin: posterior third of the lower border and the whole of the medial surface of the zygomatic arch
  • Insertion: ramus above the angle of the mandible (superior to the superficial part)
• Action: elevates the mandible
• Nerve Supply: masseteric nerve (anterior division of the mandibular nerve)
• Blood Supply:
  • Facial branch of the superficial temporal artery
  • Masseteric branch of the maxillary artery

Temporalis

• Fan-shaped muscle situated on either side of the head
• Origin: the whole of the temporal fossa, bound at the top by the inferior temporal line
• Insertion: top and medial surface of the coronoid process, and the anterior border of the ramus of the mandible
• Action:
  • Anterior fibers: elevate the mandible
  • Posterior fibers: elevate the mandible and retract the head of the condyle back into the glenoid fossa
• Nerve Supply: anterior and posterior deep temporal nerves (anterior division of the mandibular nerve)
• Blood Supply:
  • Middle temporal branch of the superficial temporal artery
  • Deep temporal branches of the maxillary artery

Lateral Pterygoid

• Short, thick, triangular muscle
• Origin:
  • Upper Head: infratemporal surface and crest of the greater wing of the sphenoid bone
  • Lower Head: lateral surface of the lateral pterygoid plate of the sphenoid bone
• Insertion: pterygoid fovea on the anterior aspect of the neck of the mandible. May also insert with structures of the TMJ
• Action:
  • Bilateral contraction: opens and protrudes the mouth
  • Alternate contraction with the opposite side: grinding or side-to-side movement
• Nerve Supply: lateral pterygoid nerve (anterior branch of the mandibular nerve)
• Blood Supply: pterygoid branches of the maxillary artery

Medial Pterygoid

• Thick quadrilateral muscle
• Origin:
  • Deep Head: medial surface of the lateral pterygoid plate of the sphenoid bone
  • Superficial Head: tuberosity of the maxilla, and pyramidal process of the palatine bone
• Insertion: medial surface of the ramus and angle of the mandible (below and behind the inferior dental foramen)
• Action:
  • Elevates the mandible
  • Protrudes the mandible in conjunction with the lateral pterygoid muscle
• Nerve Supply: medial pterygoid branch of the mandibular nerve
• Blood Supply: pterygoid branches of the maxillary artery

Accessory Muscles of Mastication

Digastric

• Has two bellies: anterior and posterior
• Origin:
  • Anterior Belly: digastric fossa on the lower border of the mandible
  • Posterior Belly: digastric notch on the mastoid process of the temporal bone
• Insertion: meet above the hyoid bone at the intermediate tendon, and that tendon is anchored to the body of the hyoid bone by a fibrous sling.
• Action:
  • Depresses the mandible
  • Elevates the hyoid bone during chewing and swallowing
• Nerve Supply:
  • Anterior Belly: mylohyoid nerve
  • Posterior Belly: digastric branch of the facial nerve VII
• Blood Supply:
  • Anterior Belly: submental branch of the facial artery
  • Posterior Belly: posterior auricular/occipital artery

Buccinator

• Forms the cheek
• Origin: pterygomandibular raphae and buccal alveolar bone (in maxillary and mandibular molars regions)
• Insertion: runs horizontally, blending with the Orbicularis Oris at the corners of the mouth
• Action:
  • Pulls the corner of the mouth back
  • Compresses the cheek against the buccal surfaces of molars
  • Regulates the vestibular region with the tongue, keeping food between the teeth during mastication
• Nerve Supply: Facial Nerve, buccal branch
• Blood Supply: Facial & maxillary arteries

Geniohyoid

• Narrow muscle situated above the medial part of the mylohyoid line
• Origin: inferior genial tubercle
• Insertion: fibres run downwards and backwards into the body of the hyoid bone
• Action: aids in deglutition and opening the mouth by depressing the mandible
• Nerve Supply: Hypoglossal Nerve
• Blood Supply: Sublingual branch of the lingual artery

Genioglossus

• Origin: Superior genial tubercle on the inner surface of the mandible
• Insertion: enters the dorsum of the tongue and forms a large fan-shaped muscle. Superior fibers pass upwards to the tip of the tongue. Inferior fibres insert on to the body of the hyoid bone.
• Action:
  • Depresses the tongue
  • Inferior fibers retract the tongue
  • Superior fibres protrude the tongue
• Nerve Supply: Hypoglossal nerve
• Blood Supply:
  • Sublingual branch of the lingual artery
  • Submental branch of the facial artery

This quiz focuses on the anatomy and physiology of the muscles involved in mastication. Learn about the four main muscles responsible for jaw movements and their innervation and blood supply. Test your knowledge on how these muscles coordinate complex jaw movements.