The orbicularis oris is a complex, multi-layered muscle located around the mouth, primarily responsible for controlling lip movements. It functions as a sphincter muscle, encircling the mouth opening.
Anatomy and Function
The orbicularis oris, also known as the musculus orbicularis oris, isn't a simple circular muscle. It's a complex structure composed of several layers of intrinsic and extrinsic fibers.
- Intrinsic Fibers: These fibers are confined within the lips themselves and are responsible for direct lip movements, such as pursing or puckering.
- Extrinsic Fibers: These fibers originate from other facial muscles and insert into the orbicularis oris. These include:
- Buccinator: Compresses the cheeks
- Levator labii superioris: Elevates the upper lip
- Depressor labii inferioris: Depresses the lower lip
- Zygomaticus major and minor: Elevate the corners of the mouth
- Risorius: Draws the corners of the mouth laterally
These extrinsic muscle attachments allow for a wide range of facial expressions involving the mouth. The orbicularis oris attaches to the dermis of the upper and lower lip through a superficial musculoaponeurotic system (SMAS).
Role in Facial Expression and Function
The orbicularis oris plays a crucial role in several functions, including:
- Speech: Shaping sounds during speech.
- Eating: Sealing the mouth to prevent food and liquid from escaping.
- Facial expressions: Expressing emotions such as smiling, kissing, and frowning.
- Playing wind instruments: Controlling airflow and embouchure.
Clinical Significance
Damage or paralysis to the orbicularis oris can result in difficulty with speech, eating, and facial expressions. This can occur due to stroke, Bell's palsy, or trauma. Reconstructive surgery may be necessary in some cases to restore function and appearance.
