### What is the Depressor Labii Inferioris? The depressor labii inferioris is a facial muscle located in the chin area. It's also known as the quadratus labii inferioris due to its quadrilateral shape. This muscle is part of a group called the buccolabial group, which controls the lips' shape, position, and movement. ### Function The primary function of the depressor labii inferioris is to pull the lower lip down and forward. This action helps in forming facial expressions associated with sadness, melancholy, and doubt. When you frown, this muscle is at work. ### Nerve Supply The muscle is supplied by the facial nerve, also known as cranial nerve number 7. ### Conditions Affecting the Muscle Several conditions can affect the depressor labii inferioris, including: - **Bell's Palsy**: A common cause of facial paralysis in the US, often linked with diabetes or pregnancy. - **Moebius Syndrome**: A rare form of facial paralysis that also affects eye movement. - **Surgery**: Accidental damage during medical procedures can cause facial paralysis. - **Trauma**: Injuries to the skull or face can damage the facial nerve. - **Tumors**: Tumors in the facial area can lead to paralysis. - **Viruses**: Certain viruses can cause facial paralysis. - **Lyme Disease**: About 11% of Lyme Disease cases involve facial paralysis. ### Conclusion Understanding the depressor labii inferioris helps in recognizing its role in facial expressions and the various conditions that can affect it.