What is the primary action of the orbicularis oris muscle?

The orbicularis oris muscle is primarily responsible for the movement of the mouth. This muscle encircles the mouth and enables various important actions, including closing the lips, puckering, and facilitating speech. It plays a crucial role in processes such as whistling, kissing, and controlling the movement of food in the mouth during chewing.

In contrast, other muscles serve functions associated with the choices provided. For instance, the action of the eye closure is primarily performed by the orbicularis oculi muscle. Nasal breathing does not involve the orbicularis oris, as it pertains more to the muscles and structures around the nasal cavity. Chewing food involves multiple muscles, primarily the masseter and temporalis, rather than the orbicularis oris, which is focused on actions related to the lips and mouth. Thus, the correct identification of the orbicularis oris's primary function as related to mouth movement is accurate.