Temporomandibular Joints Question And Answers

The Temporomandibular Joints, Teeth, And Muscles, And Their Functions

Describe the structure and functions of muscles of mastication. Deglutition/stages of deglutition. (or) Lateral pterygoid muscle. (or) Masseter muscle. (or) Muscles of mastication.
Answer:

Muscles of mastication:

• Masseter muscle:
  • It is quadrilateral in shape.

Muscles of mastication Extend:

• From the zygomatic arch to the ramus and body of the mandible.

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Muscles of mastication Insertion:

• Extends from the second molar to the posterior lateral surface of the ramus.

Muscles of mastication Structure:

• The masseter muscle is partly covered by the platysma and risorius muscle and to a variable degree with the parotid gland tissue.
• The superficial part of the muscle is separated from the deeper layer at the posterior upper part of the muscle.

Muscles of mastication Nerve supply:

• Massetric nerve – a branch of the anterior division of the mandibular nerve.

Muscles of mastication Actions:

• Elevates mandible to close the mouth to bite.

 Temporalis Structure:

• It is fan-shaped.
• It has three component parts.

 Temporalis Origin: It originates in the temporal fossa.

• Insertion:
  • Anterior border and the mesial surface of the coronoid process of the mandible.
  • Along the anterior border of ascending ramus.

 Temporalis Functions:

• The anterior part is active in clenching.
• The posterior part retracts the protruded mandible.
• The Temporalis muscle also helps in side-to-side grinding movement.

 Temporalis Nerve supply:

• 2 deep temporal branches of the mandibular nerve.

Lateral pterygoid Structure:

• It is short and conical in shape.
• It has upper and lower heads.

Lateral pterygoid Origin:

• Upper smaller head
• Infratemporal surface
• Crest of the greater wing of the sphenoid.
• Lower larger head.
• The lateral surface of the lateral pterygoid plate.

Lateral pterygoid Insertion:

• Pterygoid fovea.
• Anterior margin of articular disc and capsule of the temporomandibular joint.

Lateral pterygoid Actions:

• Depress mandible to open mouth
• Protrude the mandible.
• Contralateral abduction.
• The superior head is active during chewing and clenching of the teeth and stabilizes the condylar head during mandibular closing.
• The inferior head assists in the translation of the condyle during jaw opening.

Lateral pterygoid Nerve supply:

• The branch from the anterior division of the mandibular nerve.

Medial Pterygoid Structure:

• It is quadrilateral
• It has a small superficial and a large deep head.

Medial Pterygoid Origin:

• Superficial head
• From maxillary tuberosity
• Deep head.
• From the medial surface of the lateral pterygoid plate.

Medial Pterygoid Insertion:

• Medial surface of angle of the mandible.
• Ramus upto mandibular foramen.

Medial Pterygoid Actions:

• Elevation and lateral positioning of the mandible
• Protrudes the mandible.

Medial Pterygoid Nerve supply:

• Branch of the main trunk of the mandibular nerve.