Structure
The depressor labii inferioris is a thin, triangular muscle located in the lower lip. It originates from the mental protuberance, a bony prominence on the mandible, and inserts into the skin and fibrous tissue of the lower lip. The muscle is innervated by the facial nerve (CN VII).
Location
The depressor labii inferioris muscle is found in the lower lip and is located deep to the orbicularis oris muscle, which encircles the mouth. It is located inferior to the labium superius oris muscle, which is responsible for raising the upper lip.
Function
The main function of the depressor labii inferioris muscle is to depress (lower) the lower lip. This action helps in various facial expressions such as pouting, frowning, and grimacing. The muscle also helps in maintaining oral competence by keeping the lower lip in contact with the lower teeth during speech and swallowing.
Clinical Significance
Disorders of the depressor labii inferioris muscle can lead to difficulties in facial expression and oral function. One such disorder is paralysis of the facial nerve, which can result in weakness or paralysis of the depressor labii inferioris muscle. This can cause drooping of the lower lip and difficulty in oral function. Treatment of such disorders may involve facial nerve decompression surgery or rehabilitation therapy to improve muscle strength and function.
