Lecture 3: Muscles of Mastication PDF

Temporal region, Muscles of mastication & TMJ Lecture 3 by Anatomy department 1) Identify boundaries and contents of the temporal fossa 2) Know origin, insertion and action of muscles of mastication 3) Identify different movements of TMJ...

Temporal region, Muscles of mastication & TMJ Lecture 3 by Anatomy department 1) Identify boundaries and contents of the temporal fossa 2) Know origin, insertion and action of muscles of mastication 3) Identify different movements of TMJ 2  Norma lateralis Parietal bone Temporal lines Infra temporal fossa Temporal fossa Temporal bone Temporal lines (sup. & Inf.) Mastoid Temporal fossa Occipital bone Zygomatic arch Styloid Infra temporal fossa External process auditory meatus External auditory meatus Mastoid part of temporal Greater wing of sphenoid bone(Mastoid process)  Temporal fossa Superior temporal line A shallow depression on the side of the head (Temporal region). Bounded superiorly by the sup. temporal line and inferiorly by the zygomatic arch. Zygomatic arch The floor formed by :Frontal, Parietal, Temporal and Greater wing of sphenoid bone. These 4 Pterion bones meet at H-shaped suture---) Pterion (This suture overlies the frontal branch of middle meningeal artery)-----) Site of trephining in extradural hemorrhage. Contents of temporal fossa Temporalis muscle covered by temporal fascia. Temporal fascia is attached to Superior temporal line & upper border of zygomatic arch. Communications of temporal fossa It Communicates with infratemporal fossa via a gap deep to zygomatic arch. 6  Mandible It is the skeleton of the lower jaw the only mobile bone of the skull. It is formed of a body and two rami. The body of the mandible: Body It is horse-shoe shaped having two margins (an alveolar margin and a lower border) The upper border: carries the sockets for 16 teeth. The lower border: continues posteriorly with the posterior border of the ramus. two surfaces (external & internal). External  The mandible is formed of two halves, right and left, which unite at the symphysis Superior menti (at one year to 4 years) border inner surface 1. The surfaces A. The outer surface: it has the following features: 1.The symphysis menti: a faint median ridge representing the site of Ramus fusion between the two halves of the mandible. Body Inferior symphysis menti Outer border8 surface (cont. features of the outer surface) 2. Mental foramen: Condyle Coronoid it lies opposite the line process between the two premolars. Mandibular It is the anterior end of notch the mandibular canal. It transmits the mental nerve & vessels. 3. The oblique line Ramus extends from the anterior border of the ramus to the mental foramen. 4. Mental protuberance, Mental a median elevation close to the lower Body foramen border. It forms a projection on each side Oblique called mental tubercle. External surface line  The inner surface: It shows the followings: Head Internal surface 1.Superior and inferior Condylar process: genial tubercle: present at Neck Head and neck the lower part of the inner surface, close to the midline. 2.Mylohyoid line: It begins Mandibular F. Mylohyoid groove below and behind the last molar tooth. Then extends Lingula downwards to symphysis Mylohyoid line menti. It divides the inner surface into two fossae. Sublingual fossa: above and in front of the mylohyoid line. It is related to the sublingual salivary gland. Submandibular Submandibular fossa: It fossa lies below and behind the mylohyoid line. It is Superior & inferior related to the Sublingual submandibular salivary genial tubercle fossa 10 gland. Ramus of the mandible It projects upwards on either side from the posterior part of the body. It has 4 borders, 2 surfaces & 2 processes. Borders: 1.Upper border: it forms the mandibular notch (it stars with coronoid process and ends with condylar one. 2.Lower border: It meets the posterior border at the angle of the mandible. 3.Posterior border: It extends from the angle to the back of the condylar process. 4.Anterior border: It is continuous above with the anterior border of the coracoid process and below with the oblique line of the body. 11 Surfaces of ramus: 1.Outer (lateral) surface. 2.Inner (medial) surface. Condylar process: It is an upward projection from the posterior part of the ramus. It includes the Head and neck of the mandible. it articulates the mandibular fossa of the temporal bone forming tempro- mandibular joint. The neck of the mandible: It is the constriction below the head. Its antero-medial aspect shows a depression called pterygoid fossa or fovea. 12 Inner surface: Features of the inner surface include: Mandibular foramen: It is present at the center of ramus and leads to the mandibular canal. It transmits the inferior alveolar nerve and vessels. The margin of the foramen is irregular, it presents a prominence called lingula. Mylohyoid groove: It starts below the mandibular foramen and passes downwards and forwards to end below the posterior end of the mylohyoid line of the body. 13  Middle part of norma basalis externa Sphenoid bone Lesser wing Body Pterygoid process Lat. pterygoid plate Med. pterygoid plate Styloid process, a slender and tapering process behind the tympanic part of temporal bone Mandibular fossa, a depression in front of the tympanic part of temporal bone, for articulation with the head of the mandible Mastoid part of temporal bone, behind the tympanic part of temporal bone Mastoid notch, a depression on the medial side of mastoid process 14  Pterygoid process, formed of lateral & medial pterygoid plates with the pterygoid fossa in between. Pterygoid process Vomer, a median bone forming the posterior part of Maxillary tuberosity the nasal septum Posterior nasal apertures Maxillary tuberosity Post nasal apertures Spine of Med. plate sphenoid Pterygoid process infratemporal crest infratemporal crest Mandibular Mandibular fossa Vomer fossa Maxillary tuberosity, a rough prominence behind the last molar tooth Infratemporal surface of greater wing of sphenoid, forms the roof of the  Muscles of mastication They are developed from 1st pharyngeal arch All are innervated by mandibular N. All arise from the skull. All are inserted into the mandibular ramus They act on the TMJ (temporomandibular joint). All are concerned with MASTICATION 16 1-Temporalis Muscle Fan shaped. Origin: floor of the temporal fossa & deep surface of the temporal fascia. Insertion : in all aspects of the coronoid process except the lateral surface extending to the anterior border of ramus down till last molar 17 Action Anterior vertical fibers. Elevate the mandible Posterior horizontal fibers retract (the only retractor) the mandible Nerve supply: Anterior division of mandibular nerve. 18  Origin: by 2 heads Superficial head: Anterior 2/3 of the lower border of zygomatic arch Deep head: Posterior 1/3 of the lower border of zygomatic arch Insertion: in the lateral surface of mandibular ramus 19 Action of masseter Its deep vertical fibers elevate the mandible (antigravity muscle). Its superficial oblique fibers protrude the mandible. Nerve supply: Anterior division of mandibular nerve Relation of masseter to parotid gland and duct: the gland partially overlies the muscle and its duct crosses the masseter before piercing the buccinator 20 Facial artery pulsation can be palpated as it crosses the inferior border of the mandible immediately adjacent to the antero-inferior angle of masseter. 21 Origin by 2 heads: -Superficial head from Maxillary tuberosity -Deep head from Medial surface of lateral pterygoid plate Insertion :Medial surface of the angle of the mandible 22 Action of medial Pterygoid Elevation of the mandible (closes the mouth) Protrusion of mandible (both sides with both lateral pterygoids) Side to side movement (grinding) one side (med. and lat. pterygoids) alternating with the other side (med. and lat. pterygoids). Nerve supply: branch from trunk of mandibular nerve 23  Origin by 2 heads -Upper head: from infratemporal surface of great wing of sphenoid -Lower head: from the lateral surface of lateral pterygoid plate Insertion: Front of neck of mandible, capsule and articular disc of TMJ  Action of lateral Pterygoid Depression of mandible. Protrusion of mandible. Side to side movement. Nerve supply:- branch from anterior division of mandibular nerve. 25 SUMMARY There are 4 muscles of mastication Three are innervated from the anterior division of mandibular nerve except the med. pterygoid by the trunk of mandibular nerve The main opener of the mouth is lateral pterygoid. Lat. & medial Pterygoids & superficial fibers of Masseter protrude the mandible. Posterior fibers of temporalis retract it.  Temporomandibular joint Bilateral condylar synovial articulation between the temporal bone of the skull above and the mandible below. 27 The main components of TMJ are the joint capsule, articular disc and ligaments. 1-Fibrous capsule : attached to the margins of mandibular fossa, articular tubercle and neck of mandible. It is lined by synovial membrane. 2-Articular disc: -It is formed of fibrocartilage (Upper surface concavo-convex and the lower surface concave to fit the articulating surfaces) ---It divides the joint cavity into upper part and lower part. -It is attached to: a. The fibrous capsule. b. Tendon of lateral pterygoid muscle. - It divides the joint cavity into upper and lower compartments. 28 3-Ligaments: 1-Lateral temporomandibular ligament: It lies lateral to the fibrous capsule. -Is attached above to the zygomatic process and below to lateral surface of neck of mandible. -It limits posterior movement of mandible; thus preventing posterior dislocation and protecting the external auditory meatus. Therefore Dislocation of the joint occurs mostly in an anterior direction. 29 2-Stylomandibular ligament Extends from apex of styloid process to angle of mandible. 3-Sphenomandibular ligament Extends from spine of sphenoid to lingula. 30  Movements Of TMJ: 1-Depression : -The head of mandible rotates first on lower surface of the articular disc. -Then the head of mandible and the disc are pulled forwards by lateral pterygoids (head of mandible now articulates with the articular tubercle). -Depression of mandible can then, be performed by a hinge like movement (+ gravity). 2-Elevation: -In which the reverse to depression occurs; where the head of mandible and articular disc move backward. -Performed by temporalis, masseter and medial pterygoid muscles. 31 3-Protrusion: a. In which the head of mandible and disc move forwards & the lower teeth are thus drawn forwards. b. Done by both lateral & medial pterygoid + superficial fibers of masseter. 4-Retraction: done by posterior fibers of temporalis. 5-Side to side movements (chewing movements): a. Is performed by medial and lateral pterygoids of one side acting alternatively with the muscles of the other side. b. When medial and lateral pterygoids of one side contract, they push the chin to the opposite side. 32 33 34