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The human face has about 20 facial muscles that enable essential functions such as chewing and making facial expressions. The lips, in particular, play a critical role in facial expression, phonation, sensation, mastication, physical attraction, and intimacy. The principal muscle of the lips is the orbicularis oris, which is a circular muscle of facial expression that controls the movements of the lips.
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What You'll Learn
- The primary muscle responsible for closing the lips is the orbicularis oris
- The buccal branch of the facial nerve provides motor innervation to the orbicularis oris
- The marginal mandibular branch of the facial nerve supplies most muscles responsible for depressing the lip
- The cervical branch of the facial nerve innervates the depressor labii inferioris muscle
- The infraorbital branch of the maxillary division of the trigeminal nerve supplies the upper lip
The primary muscle responsible for closing the lips is the orbicularis oris
The human face has about 20 facial muscles, which are essential for chewing and making facial expressions. The lips, in particular, play a critical role in facial expression, phonation, sensation, mastication, physical attraction, and intimacy. The primary muscle responsible for closing the lips is the orbicularis oris.
The orbicularis oris is a circular muscle of facial expression that controls the movements of the lips. It is a complex of muscles in the lips that encircles the mouth. It is composed of four independent quadrants that interlace and give only the appearance of circularity. The muscle is innervated by the buccal and mandibular branches of the facial nerve (CN VII). The arterial blood supply of the orbicularis oris is mostly derived 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.
The upper and lower lips intersect at the mouth angle, referred to as the commissure. This is the point at which several muscles involved in lip movement attach. The orbicularis oris is unique in that it bears no direct bony attachments but is appended by the other oral muscles that attach to it. The muscle is connected with the maxilla and the septum of the nose above and with the mandible below. The proper fibres of the lips are oblique, passing from the under surface of the skin to the mucous membrane through the thickness of the lip.
The peripheral portion of the orbicularis oris, also called the extrinsic portion, originates from the modiolus and is composed of fibres from five of the many buccolabial muscles: the levator anguli oris, depressor anguli oris, buccinator, risorius, and zygomaticus major muscles. The uppermost and lowermost fibres of the peripheral portion pass into the superior and inferior labial areas, respectively, while the middle fibres decussate, so the upper half passes into the inferior labial area, and the lower half into the superior labial area. The marginal portion, also called the intrinsic portion, consists of a single or occasionally double band of muscle fibres that stem from the modiolus toward the midline, passing through the connective tissue of the lips.
The contraction of the orbicularis oris brings the lips together and closes the mouth. This action is important for mastication, as it prevents food from escaping the teeth and accumulating in the oral vestibule during eating. Isolated contraction of respective parts of the muscle causes movements such as lip pouting, twisting, and pursing.
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The buccal branch of the facial nerve provides motor innervation to the orbicularis oris
The human face has about 20 facial muscles that enable essential functions such as chewing and making facial expressions. One of these muscles is the orbicularis oris, a complex circular muscle that surrounds the mouth and forms the majority of the lips. The orbicularis oris is responsible for closing, protruding, and compressing the lips, which facilitates speech and helps produce various facial expressions.
The orbicularis oris is innervated by the buccal and mandibular branches of the facial nerve (CN VII). Specifically, the buccal branch of the facial nerve provides motor innervation to the orbicularis oris and elevators of the lip and lip angle. The facial nerve carries both motor and sensory fibres, with motor axons innervating the muscles of facial expression and the stapedius muscle. The nerve arises in the facial canal and travels across the bones of the middle ear, exiting via the petrotympanic fissure and entering the infratemporal fossa.
The marginal portions of the orbicularis oris muscle are also referred to as the labial cords. By changing their length and tension, similar to vocal cords, they produce consonantal (labial) sounds. For example, the /p/ sound in "peas" and the /b/ sound in "basket" are produced by bringing the lips together. The labial cords can also act as vibrating strings, enabling whistling or playing a wind instrument.
The arterial blood supply of the orbicularis oris is derived from several branches of the facial artery, including the superior and inferior labial branches, mental and infraorbital branches of the maxillary artery, and the transverse facial branch of the superficial temporal artery.
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The marginal mandibular branch of the facial nerve supplies most muscles responsible for depressing the lip
The human face has about 20 facial muscles that work together to control the parts of the face. Facial muscles are essential for chewing and making facial expressions. The lips, in particular, play a critical role in facial expression, phonation, sensation, mastication, physical attraction, and intimacy.
The marginal mandibular branch of the facial nerve (CN VII) arises from the facial nerve in the parotid gland at the parotid plexus. It passes anterior-ward deep to the platysma and depressor anguli oris muscles. It provides motor innervation to the muscles of the lower lip and chin, including the depressor labii inferioris muscle, depressor anguli oris muscle, and mentalis muscle. It communicates with the mental branch of the inferior alveolar nerve.
The marginal mandibular nerve may be injured during surgery in the neck region, especially during the excision of the submandibular salivary gland or neck dissections. This is due to a lack of accurate knowledge of variations in the course, branches, and relations of the nerve. An injury to this nerve during a surgical procedure can distort the expression of the smile as well as other facial expressions. Damage can cause paralysis of the muscles it supplies, resulting in an asymmetrical smile due to a lack of contraction.
The circumoral musculature, the major part of which is supplied by the marginal mandibular branch of the facial nerve, is the main factor in facial expressions. Therefore, an injury to this nerve can distort facial expressions, such as the smile. This nerve often gets injured by surgeons in operative procedures in the submandibular region, as mentioned earlier. The most frequent cause of paralysis of this nerve is iatrogenic injury during operations in the mandibular or parotid regions.
The principal muscle of the lips is the circumferential orbicularis oris, which functions primarily as a sphincter for the oral aperture. The orbicularis oris muscle is a complex of muscles in the lips that encircles the mouth. It closes the mouth and puckers the lips when it contracts.
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The cervical branch of the facial nerve innervates the depressor labii inferioris muscle
The lips are an essential aspect of the human face, playing a critical role in facial expression, speech, and physical attraction. The upper and lower lips are known as the labium superius oris and labium inferius oris, respectively. The orbicularis oris muscle is a complex of muscles in the lips that encircles the mouth and is responsible for closing or pursing the lips.
The depressor labii inferioris is a facial muscle that enables us to express feelings such as sorrow or doubt. It is located in the chin region of the face and has a quadrangular shape, also known as the quadratus labii inferioris. It is part of a broad group of muscles of facial expression called the buccolabial group.
Damage to the cervical branch of the facial nerve can lead to lower lip palsy, resulting in an asymmetrical appearance of the lip that affects smile aesthetics, speech, and articulation. This knowledge is particularly relevant for surgical procedures such as neck liposuction, where surgeons must carefully navigate between the marginal mandibular branches and the cervical nerve to mitigate risks.
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The infraorbital branch of the maxillary division of the trigeminal nerve supplies the upper lip
The human face has about 20 facial muscles that enable essential functions such as chewing and making facial expressions. The lips, in particular, play a critical role in facial expression, phonation, sensation, mastication, physical attraction, and intimacy.
The orbicularis oris muscle is a complex of muscles in the lips that encircles the mouth. It is composed of four independent quadrants that interlace and give the appearance of circularity. When it contracts, it closes the mouth and puckers the lips. The orbicularis oris muscle is supplied via the marginal mandibular branch of the facial nerve.
The trigeminal nerve, or cranial nerve V, is the largest of the twelve cranial nerves and carries both sensory and motor fibres. It has three terminal branches: the ophthalmic nerve (V1), maxillary nerve (V2), and mandibular nerve (V3). The ophthalmic and maxillary divisions carry only sensory fibres, while the mandibular division carries both sensory and motor fibres. The maxillary nerve, in particular, provides sensory supply to the mid-third of the face.
The infraorbital nerve is the terminal branch of the maxillary nerve. It carries pain, temperature, and tactile information from the region below the orbits and above the mouth, including the upper lip. Thus, the infraorbital branch of the maxillary division of the trigeminal nerve supplies the upper lip.
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Frequently asked questions
The orbicularis oris muscle is a circular muscle that controls the movements of the lips. It is a complex of muscles in the lips that encircles the mouth.
The orbicularis oris muscle closes the mouth and puckers the lips when contracted. It is innervated by the buccal and mandibular branches of the facial nerve.
The buccal branch of the facial nerve provides motor innervation to the elevators of the lip and lip angle. The platysma, which is involved in depressing the lower lip, is innervated by the cervical branch of the facial nerve. The risorius, levator labii superioris, and zygomaticus major muscles are also involved in lip movement.
