Corpus: Lateral pterygoid muscle

The lateral pterygoid muscle is a two-headed skeletal muscle that is part of the deep group of masticatory muscles. It plays a key role in protruding the jaw and opening the mouth.

The lower head of the muscle (caput inferius) is the larger portion and originates from the lateral plate of the pterygoid process of the sphenoid bone. The smaller upper head (caput superius) originates from the infratemporal surface and crest of the greater wing of the sphenoid bone.

The fibers of the upper head extend medially into the joint capsule of the temporomandibular joint, specifically attaching to the articular disc. The tendon of the lower head inserts at the condylar process of the mandible, specifically in the pterygoid fovea.

The lateral pterygoid muscle is innervated by the lateral pterygoid nerve, a branch of the mandibular nerve (cranial nerve V3).

Due to its nearly horizontal orientation, the lateral pterygoid muscle pulls the lower jaw forward (protrusion). The upper head of the muscle also moves the articular disc forward during this action. It is the only masticatory muscle essential for opening the jaw (abduction).

The medial pterygoid muscle and the masseter muscle also contribute to jaw protrusion. Unilateral contraction of these muscles produces a grinding movement of the jaw.

Muscles of the floor of the mouth, particularly the mylohyoid and digastric muscles, also assist in jaw opening. While the lateral pterygoid muscles pull the mandibular head forward, the suprahyoid and infrahyoid muscles work together to depress the lower jaw. Slight jaw opening can also occur when the weight of the lower jaw reduces the tone of the jaw-closing muscles.