The term “orbicularis” describes a category of muscles that are circular or sphincter-like. While these types of muscles exist elsewhere in the body, the name is frequently associated with two muscles in the face. These muscles are part of facial structure and expression, with one encircling the eyes and the other framing the mouth. They play distinct roles in both function and nonverbal communication.
The Orbicularis Oculi Muscle
The orbicularis oculi is a concentric muscle that encases the eye socket, lying just beneath the skin of the eyelid. Its fibers originate from the medial orbital margin and the lacrimal bone, inserting into the skin around the orbit. This muscle is functionally divided into the orbital and palpebral parts.
The larger orbital portion is responsible for the forceful, voluntary closure of the eyelids, such as when squinting in bright sunlight or protecting the eye from an impact. The palpebral section governs gentle closing, including both voluntary and involuntary blinking. This action keeps the cornea from drying out and helps clear away small debris.
A subdivision of the palpebral section, the lacrimal part, also plays a role in the drainage of tears. As the eyelid closes, this part of the muscle helps to pump tears toward the drainage ducts located in the corner of the eye.
The Orbicularis Oris Muscle
The muscle that forms the majority of the lips is the orbicularis oris. It encircles the mouth, but it is not a simple sphincter like the one around the eye. Instead, it is a complex, multi-layered muscle composed of fibers from several other facial muscles that interlace and attach to the skin of the upper and lower lips. This structure allows for a wide array of precise movements.
The orbicularis oris is divided into deep and superficial fibers. The deep fibers act to constrict the mouth, providing the sphincteric action needed to hold food and liquid inside during chewing and swallowing. This part of the muscle works with cheek muscles to press the lips against the teeth, which is important for mastication and creating a seal for sucking.
The superficial fibers are associated with facial expression and speech, allowing for the precise lip movements required for clear articulation. Actions like puckering the lips for a kiss or whistling are also accomplished by this muscle, earning it the nickname the “kissing muscle.” Musicians who play brass and woodwind instruments also rely on this muscle to form their embouchure.
Common Conditions and Concerns
Repetitive actions of the orbicularis muscles can lead to aesthetic concerns over time. The orbicularis oculi’s contraction during squinting and smiling causes the formation of dynamic wrinkles at the outer corners of the eyes, known as “crow’s feet.” Similarly, the pursing motion of the orbicularis oris contributes to vertical lines that radiate from the lips, called “smoker’s lines,” though they can appear on anyone.
Functional issues can also arise with these muscles. Benign essential blepharospasm is a condition characterized by involuntary spasms or twitching of the orbicularis oculi muscle. These twitches can range from minor fluttering to forceful contractions that interfere with vision. While harmless, these spasms can be disruptive to daily life.
Weakness in either muscle, caused by damage to the facial nerve from conditions like Bell’s palsy, can impair function. Paralysis of the orbicularis oculi can prevent a person from being able to close their eye completely, leaving the cornea exposed and at risk of drying out. Weakness in the orbicularis oris can lead to difficulty speaking clearly, keeping food in the mouth while eating, or forming a seal with the lips to drink.