Anatomy Lecture 2 PDF

Dr./ Mohamed Zakaria Kotb Lecturer of Anatomy Faculty of Medicine Cairo University Muscles of mastication  2 Superficial: temporalis and masseter 2 Deep: medial and lateral pterygoid  Summary Origin: All arise from temporal and infratemporal foss...

Dr./ Mohamed Zakaria Kotb Lecturer of Anatomy Faculty of Medicine Cairo University Muscles of mastication  2 Superficial: temporalis and masseter 2 Deep: medial and lateral pterygoid  Summary Origin: All arise from temporal and infratemporal fossa → predicated from their names 1. Temporalis → 3 temporal (fossa + line + fascia) → feel it 2. Masseter → zygomatic arch → feel it 3. Medial and lateral pterygoid: lateral pterygoid plate (medal and lateral surface) + others Lateral pterygoid plate (medal and lateral surface) + temporal fascia  Summary Insertion: All inserted into the mandible (moveable bone of TMJ) 1. Temporalis → coronoid process 2. Masseter → outer surface of ramus (feel it) 3. Lateral pterygoid: pterygoid fovea (HN) 4. Medial pterygoid: Medial surface of angle of mandible (HN)  Summary Insertion: All inserted into the mandible (moveable bone of TMJ)  Summary Nerve supply: All MS are supplied by anterior division of mandibular nerve except the medial pterygoid supplied by main trunk  Action: TMJ which is bi-condylar biaxial joint which allows 2 actions 1. Elevation and depression of mandible (i.e. closure & opening of mouth): All MS produce elevation of mandible except the Lateral pterygoid→ Produce Lowering of mandible (depression) 2. Protraction and retraction: all MS produce protraction except temporalis→ retraction. The 2 pterygoid produce protrusion to the opposite side (side to side movement) Individual muscles  Temporalis Shape Fan shaped MS covering the temporal fossa Origin All MS arise from temporal and infratemporal fossa Name→ 3 Temporal i.e. Temporal fossa floor + Inferior temporal line Deep surface of Temporal fascia covering the muscle Insertion All muscles are inserted into the ramus of the mandible tapering tendon which passes deep to zygomatic arch to be inserted into the coronoid process (its tip, anterior border & inner surface)  Tapering tendon → Deep to zygomatic arch → coronoid process Direction 1) Anterior fibers: vertically downwards of fibers: 2) Middle fibers: obliquely downwards & forwards 3) Posterior fibers: horizontally forwards NS Anterior division of mandibular nerve Action 1) Elevation of mandible by anterior fibers (anti-gravity MS) 2) Retraction by posterior fibers  Temporalis O 3 Temporal I. Coronoid process NS anterior division of mandibular n. A 1) Elevation 2) Retraction  Masseter Origin 2 heads (zygomatic arch): 1. Superficial head: lower border of zygomatic arch. 2. Deep head: deep surface of zygomatic arch. Ins All inserted into the ramus of the mandible Outer surface of the ramus of the mandible (except its posterosuperior part to give space for parotid) NS Anterior division of mandibular nerve Action 1. Elevation by deep fibers (anti-gravity MS) 2. Protrusion of the mandible by superficial fibers  Masseter zygomatic arch → lower border + inner surface Outer surface of the ramus of the mandible anterior division of mandibular nerve Elevation + Protrusion  Lateral pterygoid Origin 2 heads 1. Upper head: infratemporal surface and crest of the greater wing 2. Lower head: lateral surface of lateral pterygoid plate  Lateral pterygoid Origin 2 heads 1. Upper head: infratemporal surface and crest of the greater wing 2. Lower head: lateral surface of lateral pterygoid plate Ins. All inserted into the ramus of the mandible The muscle enters TM joint and inserted into: 1) Pterygoid fovea of neck of mandible 2) Capsule and articular disc of TMJ Capsule and articular disc of TMJ NS Anterior division of mandibular nerve Act. 1. Lowering (Depression) of mandible (lower head) 2. Protrusion: 1. Lateral and medial pterygoid of one side: protrude the mandible to the opposite side ??? 2. Lateral & medial pterygoid of both sides acting together at the same time protrude the mandible anteriorly ??? 3. Lateral and medial pterygoid muscles of both sides acting alternatively → produce side to side movement??? Lateral pterygoid → Lowering (Depression) of mandible by its lower head  Lateral and medial pterygoid → protrusion to opposite side  Medial pterygoid Origin 2 heads 1) Superficial head: maxillary tuberosity 2) Deep head: medial surface of lateral pterygoid plate (HN)  Medial pterygoid Origin 2 heads 1) Superficial head: maxillary tuberosity 2) Deep head: medial surface of lateral pterygoid plate (HN) Ins. Medial surface of angle of mandible NS Main trunk of mandibular nerve  Medial pterygoid → 4M 1. Maxillary tuberosity 2. Medial surface of pterygoid plate 3. Medial surface of angle of mandible 4. Main trunk of mandibular nerve Action Like lateral pterygoid but elevation Tempero-Mandibular Joint (TMJ)  Type: biaxial condylar synovial joint  Articular surfaces Above: Mandibular fossa and articular eminence Below: Head of mandible Covered + Separated  The articular surfaces are covered by white fibrocartilage (not hyaline)  The articular surfaces are separated by the articular disc which separates the joint cavity into upper and lower compartments. it receives the insertion of lateral pterygoid  The articular surfaces are separated by the articular disc which separates the joint cavity into upper and lower compartments. it receives the insertion of lateral pterygoid  Ligaments → 2 ST Stylo-mandibular ligament 1. Styloid process (Anterior border ??of near its tip) → angle and posterior border of mandible. 2. It separates the parotid from the submandibular gland.  Spheno-mandibular ligament: 1. It lies on the medial side 2. Spine of sphenoid → lingula of mandible.  Pterygo-mandibular ligament (raphe) Pterygoid hamulus →posterior end of mylohyoid line  Pterygo-mandibular ligament (raphe) Pterygoid hamulus →posterior end of mylohyoid line  Temporomandibular ligament 1. Thickened lateral part of the capsule 2. Zygomatic arch (Tubercle at its root) → neck of mandible (lateral & post. surfaces) 3. The only proper ligament which supports the joint.  Ligaments 2 ST Stylo-mandibular ligament: styloid angle Spheno-mandibular lig.: spine of sphenoid to lingula ‫لسان الفراشة‬ Pterygo-mandibular ligament: 2H → Hamulus to Hyoid → pterygoid hamulus mylohyoid line. Temporomandibular ligament: like the attachment of TMJ (zygomatic arch to neck of mandible)  Movements of mandible (TMJ): 1. Depression (opening the mouth): 1. Mainly: lateral pterygoid 2. Assisted by gravity and suprahyoid muscles (Digastric, mylohyoid and geniohyoid) in case of resistance 2. Elevation (closing the mouth): medial pterygoid, temporalis and masseter muscles  Protraction (forward movement): masseter + lateral and medial pterygoid of both sides acting at the same time Retraction (backwards movement): only by temporalis (posterior fibers). Side to side movement (for grinding and chewing): medial & lateral pterygoid of both sides acting alternately  Nerve supply: Auriculo-temporal nerve and nerve to masseter (Hilton’s law) Blood supply: 1.Maxillary artery. 2.Superficial temporal artery.  Applied anatomy The mandible is dislocated anteriorly only Mechanism: With the mouth open, the condyles are present below the articular eminence (tubercle) + sudden violence as convulsive yawn → 1 or both condyles may be displaced into the infratemporal fossa in front of articular tubercle