The mentalis muscle is a paired central

muscle Skeletal muscles (commonly referred to as muscles) are Organ (biology), organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other ...

of the lower lip, situated at the tip of the

chin The chin is the forward pointed part of the anterior mandible ( mental region) below the lower lip. A fully developed human skull has a chin of between 0.7 cm and 1.1 cm. Evolution The presence of a well-developed chin is considered to be one ...

. It originates from the mentum of the mandible, and inserts into the soft tissue of the chin. It is sometimes referred to as the "pouting muscle" due to it raising the lower lip and causing chin wrinkles.

Structure

The mentalis muscle originates from the mental protuberance of the

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bon ...

near the midline. It inserts into the soft tissue and

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...

of the

Function

The mentalis muscle causes a weak upward-inward movement of the soft tissue complex of the

. This raises the central portion of the lower lip. In the setting of lip incompetence (the upper and lower lips do not touch each other at rest), the mentalis muscle contraction can bring temporary but strained oral competence. In conjunction with the orbicularis oris muscle (for the upper lip), the mentalis muscle allows the lips to "pout". Externally, the mentalis muscle contraction causes

wrinkling A wrinkle, also known as a rhytid, is a fold, ridge or crease in an otherwise smooth surface, such as on skin or fabric. Skin wrinkles typically appear as a result of ageing processes such as glycation, habitual sleeping positions, loss of bo ...

and dimpling of the

on the chin, as used in expressions of doubt or displeasure.

Clinical significance

The mentalis muscle can be easily assessed using

ultrasound Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies fr ...

Geniospasm

Geniospasm is a genetic movement disorder of the mentalis muscle. It involves repetitive contraction of the muscle, with episodes lasting between seconds and hours. Certain medications may be used to treat it, such as haloperidol and benzodiazepines. Injection of

botulinum toxin Botulinum toxin, or botulinum neurotoxin (BoNT), is a neurotoxic protein produced by the bacterium ''Clostridium botulinum'' and related species. It prevents the release of the neurotransmitter acetylcholine from axon endings at the neuromu ...

(permanently paralysing the muscle) may be more effective.

Cosmetics

The mentalis muscle may be partially paralysed using botulinum toxin to reduce wrinkling of the skin of the chin. This may be done for cosmetic purposes.

Additional images

File:Gray176.png, Outer surface of

. Mentalis is indicated by the red circle at left. File:Mentalis animation small.gif, Position of mentalis (red). File:Braus 1921 376.png, Action of the mentalis muscle.

References

{{Authority control Muscles of the head and neck