Muscles Of Head And Neck
- It is a synovial, bicondylar joint between the mandibular fossa and articular tubercle of temporal bone above and the head of mandible below. The joint is completely divided into two compartments (upper and lower) by e fibro cartilaginous articular disc. Ligaments ofTM joints are fibrous capsule, lateral temporomandibular ligament, and stylomandibular ligament.
- The articular disc is a fibrocartilaginous disc which divides joint cavity into an upper and a lower compartment. The upper compartment permits gliding movement and the lower compartment permits rotatory as well as gliding movement, the articular disc represents the degenerated primitive insertion of lateral pterygoid: Central portion of articular disc is least vascular. Articular disc acts as shock absorber, prevents friction between articular surfaces and also has proprioceptive function. Articular disc also increases the area of contact and hence helps in distribution of weight across the joint.
- There are following movements in TMjoints:-
- Protrusion (protraction of chin):- Lateral and medial pterygoid of both sides acting together, assisted by superficial fibers of masseter.
- Retraction (Retraction of chin): - Posterior fibers of temporalisassisted by deep fibers of masseter.
- Elevation (Closing of mouth): -Masseter, temporalis, and medial pterygoid of both sides.
- Depression (opening of mouth) :- Both lateral pterygoidsassisted by digastric, mylohyoidandgeniohyoid
- Side to side (lateral) movement:-Lateral and medial pterygoidsof one side acting alternately with each other.
- Dislocation of mandible occurs when mouth is opened too widely by excessive contraction oflateral pterygoid.
- Head of the mandible slips anteriorly into infratemporal fossa.
- A TM joint is supplied by auriculotemporal nerveand masseteric nerve.