Corpus: Orbicularis oris muscle
from Latin: orbis - circle, disc; os - mouth
1. Definition
The orbicularis oris muscle is a circular muscle that surrounds the mouth opening, ensuring the closure of the lips. It is part of the facial expression musculature.
2. Course
The orbicularis oris muscle originates from the anterior surfaces of the alveolar ridges of the upper (maxilla) and lower jaw (mandible).
Its fibers run in concentric circles around the mouth. At the corners of the mouth, the fibers of the orbicularis oris muscle merge with fibers from the buccinator muscle and other facial muscles, forming a structure known as the modiolus anguli oris.
3. Innervation
The orbicularis oris muscle is innervated by the buccal branches of the facial nerve (cranial nerve VII).
4. Function
When the orbicularis oris muscle contracts, it closes or purses the lips. This muscle is essential for producing certain lip sounds, such as "B" and "P," during speech. It also plays a key role in forming the correct lip shape when playing wind instruments, such as brass instruments.
The muscle is fused with the underlying skin, causing the skin to move with the muscle. The folds that appear around the mouth when the muscle contracts are commonly referred to as "smokers lines".