Which muscle acts to open the jaw?

The lateral pterygoid muscle is primarily responsible for opening the jaw. This muscle plays a crucial role in the movement of the mandible. It has two distinct heads, and its contraction pulls the head of the mandible forward and downward, which allows the mouth to open. This function is essential for actions like speaking, eating, and singing.

While other muscles associated with jaw movement, such as the medial pterygoid and temporalis, are involved in closing the jaw and elevating the mandible, they do not function to open the jaw. The omohyoid muscle, on the other hand, has no direct role in jaw movement; it is involved in depressing the hyoid bone and thus influences the position of the larynx. Understanding the specific roles of these muscles highlights why the lateral pterygoid is the key player in the action of opening the jaw.