Dominic Stone
The orbicularis oris muscle is a circular muscle located in the mouth that controls the movement of the lips. It is a complex muscle that closes the mouth and puckers the lips when contracted. The muscle is made up of four independent quadrants that interlace, giving the appearance of circularity. The bulk of the muscle fibres originate from the buccinator muscle, which is responsible for compacting the cheek.
| Characteristics | Values |
|---|---|
| Name | Orbicularis Oris |
| Type | Circular muscle of the facial expression |
| Location | Mouth |
| Function | Controls the movements of the lips |
| Innervation | Buccal and mandibular branches of facial nerve (CN VII) |
| Arterial Blood Supply | Superior and inferior labial branches of the facial artery, mental and infraorbital branches of maxillary artery, and the transverse facial branch of superficial temporal artery |
| Muscle Fibers | Oblique |
| Muscle Fibers Origin | Buccinator, levator anguli oris, depressor anguli oris, risorius, and zygomaticus major |
| Muscle Actions | Closes the mouth, puckers the lips, and produces various lip movements such as pouting, twisting, and pursing |
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What You'll Learn
The orbicularis oris muscle
The orbicularis oris is composed of four independent quadrants that interlace and give only the appearance of circularity. It 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 peripheral portion of the orbicularis oris muscle, also called the extrinsic portion, originates from the modiolus and arises from the fibres of the five buccolabial muscles that attach to it. These modiolar muscles include the levator anguli oris, depressor anguli oris, buccinator, risorius, and zygomaticus major muscles. However, most of the fibres that comprise the orbicularis oris originate from the buccinator muscle.
The marginal portion, also known as the intrinsic portion, consists of a single or occasionally double band of muscle fibres. They stem from the modiolus toward the midline, passing through the connective tissue of the lips. The fibres curl upon themselves, forming the vermilion border of the lips at the junction between the skin and mucous membrane.
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The buccinator muscle
The buccal fat pad covers the outer surface of the deep part of the buccinator, separating it from the ramus of the mandible, masseter, and temporalis muscles. The buccinator receives arterial blood supply mainly from the buccal artery, a branch of the maxillary artery, and some branches of the facial artery. The veins draining the buccinator empty into the pterygoid plexus and internal maxillary vein.
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The depressor anguli oris muscle
The depressor anguli oris is a paired triangular muscle, with one on each side of the face. It originates from the oblique line and mental tubercle of the mandible, located on the anterior aspect of the bone. The muscle fibres converge into a narrow fascicle running superiorly towards the angle of the mouth. At this point, it blends with other muscles that insert into the lips. The depressor anguli oris forms a fibromuscular structure called the modiolus, where it converges and interlaces with other muscles.
The depressor anguli oris is supplied by the marginal mandibular branch of the facial nerve, also known as Cranial nerve VII. It is also supplied by the inferior labial and mental arteries, which are branches of the facial artery and maxillary artery, respectively. The venous blood is drained through the facial vein into the internal jugular vein. Damage to the marginal mandibular branch of the facial nerve may cause paralysis of the depressor anguli oris muscle, which may result in an asymmetrical smile.
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The risorius muscle
The arterial blood supply to the risorius muscle comes from the facial artery and its branch, the transverse facial artery. The facial vein and transverse facial vein drain deoxygenated blood from the muscle, eventually draining into the internal jugular vein. The risorius muscle is located within the deep portion of the superficial musculoaponeurotic system (SMAS), a fibrous network containing facial muscles.
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The zygomaticus major muscle
Acting in coordination with other muscles that elevate the lip, the zygomaticus major muscle curls the upper lip to produce facial expressions such as smiling, disdain, contempt, or smugness. It is also one of the "'laughing muscles", along with the risorius muscle. The average zygomaticus major muscle can contract with a force of 200 g.
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Frequently asked questions
The orbicularis oris muscle is responsible for closing the mouth and compressing the lips.
The orbicularis oris is a circular muscle located in the mouth. It is made up of four independent quadrants that give the appearance of circularity.
The orbicularis oris muscle controls the movement of the lips. It can close the mouth, approximate the lips to the maxilla and mandible, or purse the lips.
The proper fibres of the orbicularis oris are oblique and pass from the under surface of the skin to the mucous membrane through the thickness of the lip.
The buccinator muscle is involved in oral activities such as whistling, sucking, and playing wind instruments. It compresses the cheek and helps to hold food between the teeth during chewing.
