Muscles of Mastication Flashcards
Describe the mandible:
The mandible is the lower jawbone that forms the lower jaw. It has several key features, including:
Coronoid process: a thin, triangular eminence located on the anterior (front) part of the mandible
Condyloid process/Head: a rounded eminence located on the posterior (back) part of the mandible that forms the temporomandibular joint (TMJ)
Alveolar process/ridge: a bony ridge that contains the sockets for the teeth
Ramus: a vertical part of the mandible that connects the coronoid process to the condyloid process
Mental protuberance: a bony prominence located on the anterior part of the mandible, also known as the chin
Mental foramen: a small opening located on the anterior part of the mandible through which the mental nerve exits
Mandibular foramen: a small opening located on the posterior part of the mandible through which a branch of the trigeminal nerve (V3) enters
Describe the Temporomandibular Joint
The temporomandibular joint (TMJ) is a modified hinge synovial joint that connects the mandible to the temporal bone. It is composed of:
Mandibular fossa: a depression located on the temporal bone that receives the condyloid process of the mandible
Articular tubercle: a bony prominence located on the temporal bone that forms the TMJ
Fibrocartilage: a type of cartilage that covers the articular surfaces of the TMJ
Articular disc: a fibrocartilaginous disc that separates the articular surfaces of the TMJ
What is mastication ?
Mastication is the process of chewing food which is facilitated by muscles masseter, temporalis, Medial pterygoid and lateral pterygoid
Describe the Masseter:
Located in the zygomatic region of the face
Origin - zygomatic arch
Insertion - ramus and angle of the mandible laterally
Innervation - mandibular branch of the trigeminal nerve (CN V), specifically the masseteric nerve
Function - elevate and protrude mandible
Describe the temporalis:
Origin - temporal fossa
Insertion - coronoid process of the mandible
Function - Elevate & Retract mandible
Innervation - mandibular branch of the trigeminal nerve (CN V), specifically through the deep temporal nerves
Anterior fibres elevate mandible and posterior fibres retract mandible
Describe the Lateral Pterygoid:
Bilateral muscle (one on each side of the head
Superior head originates at greater wing of the sphenoid bone
Inferior head originates from the lateral surface of the lateral pterygoid plate of sphenoid bone
Function - Depress & Protrude mandible
Insertion - neck of the mandible and the articular disc of the temporomandibular joint
Innervation - mandibular branch of the trigeminal nerve (CN V), specifically the pterygoid branches
Review the movements involved in mastication:
Elevation: the movement of the mandible upwards, which is facilitated by the masseter, temporalis, and medial pterygoid muscles
Depression: the movement of the mandible downwards, which is facilitated by the lateral pterygoid muscle
Protraction: the movement of the mandible forwards, which is facilitated by the masseter, temporalis, and lateral pterygoid muscles
Retraction: the movement of the mandible backwards, which is facilitated by the temporalis and medial pterygoid muscles
What movement of the mandible does the TMJ allow for ?
Rotation: the head of the mandible rotates on the articular disc
Translation: the head of the mandible and the articular disc move anteriorly (forwards) on the mandibular fossa
Describe a standard dislocation to the TMJ :
Can occur due to trauma or excessive opening of the mouth. The condyloid process of the mandible usually dislocates anteriorly, and the muscles of mastication tighten and hinder repositioning.
Describe the Medial Pterygoid:
Superficial aspect originates from maxillary tuberosity and the palatine bone
Deep aspect originates from lateral pterygoid plate
Insertion - medial surface of the ramus and angle of the mandible
Function - elevate and protrude mandible
Innervation - mandibular branch of the trigeminal nerve (CN V), specifically the pterygoid branches
Describe the cranial nerve V/ trigeminal:
Cranial nerve V, also known as the trigeminal nerve, is a mixed nerve that provides sensory innervation to the face, oral, nasal, and orbital cavities, as well as motor innervation to the muscles of mastication
What are the divisions of the cranial nerve V ?
Ophthalmic division (V1): provides sensory innervation to the eye and surrounding areas
Maxillary division (V2): provides sensory innervation to the mid-face and surrounding areas
Mandibular division (V3): provides motor innervation to the muscles of mastication and sensory innervation to the lower face and surrounding areas
