Lateral pterygoid muscle
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The lateral pterygoid muscle, also known as pterygoideus externus or external pterygoid muscle, is one of the muscles of mastication.
action: opening of the mouth, retrusion of the temperomandibular joint, side-to-side movement of the jaw 1
The lateral pterygoid is a short and thick muscle with a somewhat conical form. It extends almost horizontally, posteriorly, and laterally between the infratemporal fossa and the condyle of the mandible. It has two heads: an upper (superior) and a lower (inferior).
The superior part arises from the lower part of the lateral surface of the greater wing of the sphenoid bone and the infratemporal crest. It inserts into the temporomandibular joint capsule and the temperomandibular disc.
The superior part is active during retrusion (opposite of protrusion) and ipsilateral jaw movement. It is also essential in pulling the capsule and disc forward during mouth opening, thereby maintaining normal relationship between the condyle of the mandible and the disc of the tempoeromandibular joint.
The inferior part is responsible for opening of the mouth, protrusion, and contralateral jaw movement.
Hyperactivity of the lateral pterygoid muscle has been described in temperomandibular joint internal derangement, especially with longstanding anterior displacement of the disc without recapture. Thickening of the tendon (inferior part) can give rise to the "double disc sign".
Anatomical variants of the lateral pterygoid include:
variation in number of heads
three headed variant with an inner head originating at the greater wing of the sphenoid
single headed variant
variation in number of insertions
three insertion sites: articular disc, TMJ capsule, condyle of the mandible
single insertion site at the condyle only