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The main muscle responsible for closing the lips is the orbicularis oris muscle. This muscle is a complex, multi-layered muscle that encircles the mouth and is covered externally by skin and internally by mucosa. When the orbicularis oris muscle contracts, it pulls the lip tissue centrally, closing the lips and allowing for actions such as eating, drinking, whistling, and kissing. The proper fibres of the lips pass from the under surface of the skin to the mucous membrane, through the thickness of the lip. This muscle is innervated by the buccal and mandibular branches of the facial nerve (CN VII) and receives arterial blood supply from various branches of the facial and maxillary arteries.
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What You'll Learn
- The main muscle of the lip, orbicularis oris, closes the mouth and puckers the lips
- The levator labii superioris and levator labii superioris alaeque nasi muscles elevate the upper lip
- The depressor anguli oris, depressor labii inferioris, and mentalis muscles depress the lower lip
- Zygomaticus major and risorius muscles elevate the angle of the mouth
- The platysma muscle originates in the neck and inserts into the chin
The main muscle of the lip, orbicularis oris, closes the mouth and puckers the lips
The orbicularis oris muscle is the main muscle of the lip. It is a complex, multi-layered muscle that encircles the mouth and is covered externally by skin and internally by mucosa. The orbicularis oris muscle is responsible for pulling the lip tissue centrally, allowing for actions such as eating, drinking, whistling, and kissing. It is also one of the muscles used in playing brass and some woodwind instruments.
The muscle is composed of four independent quadrants that interlace and give the appearance of circularity. It is not a true sphincter, as was once thought, as it consists of numerous strata of muscular fibres surrounding the mouth, with fibres running in different directions. The deep fibres of the muscle act as a constrictor and are responsible for the sphincteric action of the mouth.
The orbicularis oris muscle is innervated by the buccal and mandibular branches of the facial nerve (CN VII). The arterial blood supply is derived mostly from the superior and inferior labial branches of the facial artery, mental and infraorbital branches of the maxillary artery, and the transverse facial branch of the superficial temporal artery.
Contraction of the orbicularis oris muscle closes and protrudes the lips, and results in the formation of marionette lines in the lateral perioral region. These lines give the illusion of sadness. The muscle also contributes to the form and shape of the lips.
Some newborns may be born with an absence of the orbicularis oris on one side of the face, resulting in a partial droop on the affected side. Tension on this muscle can result in vertical lip lines on the upper and lower lips. Treatment for these lines consists of botulinum toxin injected directly into the muscle.
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The levator labii superioris and levator labii superioris alaeque nasi muscles elevate the upper lip
The lips are comprised of the orbicularis oris muscle, which is covered externally by skin and internally by mucosa. The upper lip, in particular, is controlled by several mimetic muscles that elevate and depress it.
The levator labii superioris is a short, paired triangular muscle of the face. It is part of the buccolabial group of muscles of facial expression, which work in synergy to control the shape, posture and movements of the lips. This muscle originates from the zygomatic process of the maxilla and the maxillary process of the zygomatic bone, just superior to the infraorbital foramen. It courses inferomedially towards the upper lip, gradually tapering and becoming triangular in shape. It inserts between the levator labii superioris alaeque nasi, orbicularis oris and zygomaticus minor by blending with the muscles of the upper lip.
The levator labii superioris alaeque nasi muscle, translated from Latin, is the "lifter of both the upper lip and of the wing of the nose". It is attached to the upper frontal process of the maxilla and inserts into the skin of the lateral part of the nostril and upper lip. This muscle is also sometimes referred to as "the Elvis muscle" because it allows for elevation of the lip, which is essential for forming the lip snarl singer Elvis Presley was well known for.
Together, the levator labii superioris and levator labii superioris alaeque nasi muscles elevate the upper lip, helping to produce various facial expressions, such as smiling or disdain.
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The depressor anguli oris, depressor labii inferioris, and mentalis muscles depress the lower lip
The lips play a critical role in facial expression, phonation, sensation, mastication, physical attraction, and intimacy. The upper and lower lips are comprised of the sphincteric orbicularis oris muscle, which is covered externally by skin and internally by mucosa. The position and movement of the lips is influenced by several mimetic muscles that elevate and depress the lips. These muscles attach to a connective tissue thickening at the oral commissures known as the modiolus.
The depressor anguli oris, depressor labii inferioris, and mentalis muscles are all involved in depressing the lower lip. The depressor anguli oris (DAO) is a triangular muscle that originates from the inferior border of the mandible and inserts into the corner of the mouth, depressing it. The depressor labii inferioris (DLI) is a muscle that overlays the DAO and attaches to the skin of the lip, depressing the lower lip. The mentalis muscle is also involved in depressing the lower lip, although its specific origin and insertion are unclear.
The DAO and DLI muscles can be targeted with botulinum toxin injections to relax their hyperdynamic function and create symmetry in patients with perioral asymmetry. This can help elevate the corners of the mouth and improve the appearance of a smile.
It is important to note that the elevators of the upper lip include muscles such as the levator labii superioris and the levator labii superioris alequae nasi muscle. These levator muscles attach to the lower lip at or near the modiolus to elevate the lips or oral commissure.
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Zygomaticus major and risorius muscles elevate the angle of the mouth
The orbicularis oris muscle is the main muscle of the lip and is responsible for pulling the lip tissue centrally, allowing for actions such as eating, drinking, whistling, and kissing. It is a complex, multi-layered muscle that encircles the mouth and is composed of four independent quadrants that interlace and give only an appearance of circularity. The contraction of this muscle closes and protracts the lips.
The zygomaticus major and risorius muscles elevate the angle of the mouth. The zygomaticus major is a thin, paired facial muscle that arises from the lateral surface of the zygomatic bone and extends diagonally to the angle of the mouth. It contributes to the formation of the modiolus by interlacing with several other facial muscles. The modiolus is a fibromuscular hub located at the angles of the mouth where the majority of the mouth muscles are connected. The zygomaticus major is innervated by the zygomatic and buccal branches of the facial nerve (CN VII). Its blood supply stems from the superior labial branch of the facial artery.
The risorius is a muscle that contributes to laughing and is, therefore, deemed a "laughing muscle". It is one of the elevators of the upper lip.
The levator anguli oris is another slender, sheet-like muscle that arises from the canine fossa of the maxilla and moves towards the angle of the mouth to attach to the modiolus. It is innervated by the zygomatic and buccal branches of the facial nerve (CN VII), while its blood supply is provided by the superior labial branch of the facial artery and the infraorbital branch of the maxillary artery. The levator anguli oris elevates the angles of the lips, contributing to producing a smile, together with the risorius, zygomaticus major and minor.
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The platysma muscle originates in the neck and inserts into the chin
The orbicularis oris muscle is the main muscle of the lips and is responsible for pulling the lip tissue centrally, allowing for actions such as eating, drinking, whistling, and kissing. It is a complex, multi-layered muscle that encircles the mouth. The upper and lower lips are comprised of the sphincteric orbicularis oris muscle, which is covered externally by skin and internally by mucosa.
Contraction of this muscle closes and protracts the lips. The position and movement of the lips are acted upon by several mimetic muscles that elevate and depress the lips. These muscles attach to a connective tissue thickening at the oral commissures referred to as the modiolus. Elevators of the upper lip include the levator labii superioris and the levator labii superioris alaeque nasi muscle.
The platysma muscle is a flat muscle that originates in the neck and inserts into the chin at the commissures of the mouth and into the anterior one-third of the oblique line of the mandible. It is involved in the depression of the lower lip and receives its innervation via the cervical branch of the facial nerve. The depressor labii inferioris muscle is also innervated by a distinct lower cervical branch of the facial nerve. This branch lies approximately 2 cm below the mandible and travels independently toward the depressor labii inferioris muscle.
Other lower lip depressors include the depressor anguli oris, depressor labii inferioris, and the mentalis muscles. The risorius muscle, which may arise from the platysma muscle, elevates the angle of the mouth. The DAO is a triangular muscle that arises from the inferior border of the mandible and inserts into and depresses the corner of the mouth. It is overlaid by the more medial and triangular DLI, which depresses the lower lip.
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Frequently asked questions
The orbicularis oris muscle is the main muscle responsible for closing the lips.
The orbicularis oris muscle is a complex, multi-layered muscle that encircles the mouth. It is composed of four independent quadrants that interlace and give the appearance of circularity.
The orbicularis oris muscle controls the movement of the lips and is involved in various functions such as eating, drinking, whistling, kissing, and playing certain musical instruments.
The orbicularis oris muscle contracts, bringing the lips together and closing the mouth. It works in coordination with other muscles and nerves in the facial region to enable various facial expressions and functions.
