The Mentalis Muscle is a small, paired facial muscle located in the center of the lower lip and at the tip of the chin (mentum). It is also known as the "pout muscle" because when contracted, it lifts the lower lip, causing chin wrinkles and a duck-like expression.

Anatomy

Morphology and Connection Points

The Mentalis Muscle originates from the mental process of the mandible (the midline of the jawbone), and its fibers insert into the skin of the chin and the soft tissue of the lower lip. It interacts with the orbicularis oris muscle and lies deep to the depressor labii inferioris muscle. This location enhances the mentalis muscle's influence on the skin of the lower lip and chin. During muscle movements, characteristic dimpling and creases occur in the skin of the chin.

Embryological Origin and Classification

The Mentalis Muscle is a member of the facial expression muscles and embryologically originates from the second pharyngeal arch. Functionally, it controls the movement of the lower lip and chin skin, playing a role particularly in lip closure and facial expressions. When classified, it is among the muscles specifically responsible for lip movements and is a key component of the facial expression muscles.

Nerve Innervation and Vascular Supply

The Mentalis Muscle receives motor innervation from the marginal mandibular branch of the facial nerve (cranial nerve VII). Blood circulation is provided by branches of the facial artery. The superficial and deep structures of the muscle ensure adequate blood supply and function of the nerves and vessels within the muscle.

Function and Clinical Relationships

The Mentalis Muscle is one of the primary muscles that pulls the lower lip upward and inward. This muscle is particularly active in producing expressions of sullenness, suspicion, or displeasure. It also contributes to lip puckering. In cases of lip inadequacy, such as when the lips cannot be fully closed, the mentalis muscle plays a role in providing temporary oral adequacy. The muscle's contraction results in noticeable dimpling and wrinkles in the skin of the chin. Geniospasm (Jaw Tremor Syndrome) is a condition characterized by involuntary, rhythmic contractions of the mentalis muscle, attacks that can last from seconds to hours, and is associated with a genetic predisposition. While botulinum toxin injections are the most effective treatment, medications such as haloperidol and benzodiazepines can also be used for symptom control. Because overactivity of the mentalis muscle can lead to wrinkles in the chin area, Botox injections are widely preferred for aesthetic purposes to eliminate these wrinkles; however, improper dosing can lead to weakness in lip movement. Additionally, hyaluronic acid fillers are used to improve the chin contour and enhance the aesthetic appearance of the mentalis muscle. Ultrasonography, a non-invasive method for assessing muscle structure and function, is an effective imaging tool for both muscle condition and the diagnosis of potential pathologies.