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The zygomaticus major muscle is a thin, paired facial muscle that extends diagonally from the zygomatic bone to the angle of the mouth. It is part of the buccolabial group of facial muscles, which form the structure and function of the cheeks and lips. The zygomaticus major muscle is responsible for pulling the angle of the mouth superolaterally, creating facial expressions such as smiling, laughing, disdain, contempt, or smugness. This muscle is also known as the laughing muscle due to its role in creating laughter. The zygomaticus major muscle is innervated by the zygomatic and buccal branches of the facial nerve and is supplied by the superior labial artery, a branch of the facial artery. In addition to its role in facial expressions, the zygomaticus major muscle may be used in reconstructive surgery to replace lost tissue in the lips.
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What You'll Learn
The zygomaticus major muscle
The main action of the zygomaticus major muscle is to pull the angle of the mouth superolaterally, elevating and everting it. In coordination with other buccolabial muscles, it facilitates speech and creates facial expressions. Specifically, the zygomaticus major, in conjunction with the risorius muscle, produces the expression of smiling and laughter, deepening the nasolabial groove.
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Zygomatic bone
The zygomatic bone, also known as the zygoma, cheekbone, or malar bone, is a paired, irregularly shaped bone of the skull. It is situated at the upper and lateral part of the face, just below each eye, and extending upward to the outer side of each eye. The zygomatic bone is nearly quadrangular or diamond-shaped and features three surfaces, five borders, and two processes.
The zygomatic bone contributes to the formation of the zygomatic arch, also known as high cheekbones, which are considered physically attractive in some cultures. The zygomatic arch is formed by the temporal process of the zygomatic bone, along with the zygomatic process of the temporal bone. The zygomatic bone also forms the walls of the temporal and infratemporal fossae, and the floor and lateral wall of the bony orbit, or eye socket. The orbital surface of the zygomatic bone is smooth and concave, facing towards the orbit and forming the anterolateral part of its floor and the anterior part of its lateral wall.
The zygomatic bone has three surfaces: the lateral (or facial) surface, the posteromedial surface, and the orbital surface. The lateral surface is smooth and convex, facing towards the outside of the face. It features a small opening called the zygomaticofacial foramen, which allows for the passage of the zygomaticofacial nerve, artery, and vein between the orbit and the face. The orbital surface, as mentioned earlier, forms the anterolateral part of the orbit's floor and the anterior part of its lateral wall. It features the zygomatico-orbital foramen, which is a gateway to the bony canal within the zygomatic bone. This canal branches into the zygomaticofacial and zygomaticotemporal canals, transmitting nerves and vessels to the corresponding surfaces of the zygomatic bone.
The zygomatic bone articulates with several other bones of the face, including the frontal bone, sphenoid bone, temporal bones, maxillary bones, nose, jaw, portions of the eye, and bones just in front of the ears. The zygomatic bone is important for protecting the more delicate features of the face, such as the arteries, nerves, veins, and organs that lie below the surface. Additionally, the grooves and indentations of the upper zygomatic bone provide space for muscles to insert in the forehead and upper portion of the skull, allowing the zygomatic bone to connect with the upper portion of the skull.
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Facial muscles
The human face has about 20 facial muscles on each side, responsible for essential tasks such as chewing and making facial expressions. These muscles are located throughout the face, including the ears, mouth, forehead, nose, and eyes. Facial muscles are also called craniofacial muscles, and they attach to different places on the skull. They originate from bone or fascia and insert into the skin, manipulating the skin and soft tissues to enable movement and expressions.
The zygomaticus major muscle is a thin, paired facial muscle that extends diagonally from the zygomatic bone to the angle of the mouth. It is part of the buccolabial group of facial muscles, which also includes the levator labii superioris alaeque nasi, levator labii superioris, zygomaticus minor, levator anguli oris, risorius, depressor labii inferioris, depressor anguli oris, mentalis, orbicularis oris, incisivus superior, and inferior and buccinator muscles. These muscles form the structure and functions of the cheeks and lips, such as pulling the angle of the mouth superolaterally and facilitating speech and facial expressions.
The zygomaticus major muscle is innervated by the zygomatic and buccal branches of the facial nerve (CN VII) and is supplied by the superior labial artery, a branch of the facial artery. It contracts to pull the angle of the mouth upwards and outwards, contributing to expressions such as smiling, disdain, contempt, or smugness. This muscle is also responsible for deepening the nasolabial furrow and raising the upper lip to bare the upper teeth.
The zygomatic bone, from which the zygomaticus major muscle originates, is a prominent feature of the face. It forms the zygomatic arch, which is prone to fractures that can result in spasms and limited mouth opening. The zygoma also serves as an origin point for the masseter muscle and an attachment point for the temporalis and other muscles.
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Zygomatic arch
The zygomatic arch, also known as the cheekbone, is a specific anatomical structure within the zygomatic bone (the cheekbone). It is a bar of bone that runs horizontally along the side of the head, positioned in front of the ear and slightly above the tragus. The arch is formed by the temporal process of the zygomatic bone in its front section, and the temporal bone's zygomatic process in the back. The two are united by an oblique suture (the zygomaticotemporal suture), which runs diagonally downward and backward across the arch.
The zygomatic arch is a significant structure in evolutionary biology, as it is part of the structures derived from the ancestral single temporal fenestra of the synapsid ancestor of mammals. The arch is typical of Synapsida ("fused arch"), a clade of amniotes that includes mammals and their extinct relatives. In human evolution, the zygomatic arch has generally become more slender. However, it is still more prominent in some populations and is larger and more robust in males.
The masseter muscle, important for chewing, arises from the lower edge of the arch, and the tendon of the temporal muscle passes through the middle of the arch to gain insertion into the jawbone. The zygomatic arch is particularly large and robust in herbivorous animals, including baboons and apes. In humans, a large zygomatic arch has been observed in early hominids such as Australopithecus robustus, suggesting a herbivorous diet.
Isolated fractures of the zygomatic arch can cause trismus, or spasms, through impingement on the temporal muscle. Depressed fractures of the arch can also cause trismus by impinging on the coronoid process of the mandible or by directly injuring the muscles of mastication. The zygomatic bone, or zygomaticum, also serves as a point of origin of the masseter muscle and a point of attachment for the zygomaticus and temporalis muscles.
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Zygomatic fractures
The zygomatic bone forms the zygomatic arch, which is a major structural component of the midface. It is formed by contributions from the temporal bone and the zygoma and is crucial for the structural integrity and aesthetic appearance of the midface.
The zygomatic arch is susceptible to fractures due to its anatomical structure. It typically bows inward, which can create a visible depression under the thin skin of the lateral midface. Depressed fractures of the zygomatic arch can lead to trismus, or spasms, by impinging on the muscles of mastication or the temporal muscle. The superomedial portion of the zygoma is particularly thin and prone to buckling under impact, often resulting in fractures of the orbital floor.
The management of zygomatic fractures depends on the specific patient and the severity of the fracture. Treatment can range from conservative observation to advanced techniques such as open reduction with internal fixation. It is important to evaluate patients with zygomatic fractures for potential concomitant fractures of the orbit due to the complex anatomy of the midface and the zygomatic bone's articulations with multiple facial bones.
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Frequently asked questions
The zygomaticus major muscle is a thin, paired facial muscle that extends diagonally from the zygomatic bone to the angle of the mouth. It is part of the buccolabial group of facial muscles.
The zygomaticus major muscle is responsible for pulling the angle of the mouth superolaterally, creating facial expressions such as smiling, laughing, disdain, contempt, or smugness.
The zygomatic arch is formed by the articulation of the zygoma with the zygomatic process of the temporal bone. It is a frequent site for wire or bone-plate fixation following fracture.
The zygoma is a quadrilateral-shaped bone that forms the lateral buttress of the face, the inferior and lateral orbital rim, and a portion of the orbital floor. It provides an origin for the masseter muscle and attachment points for the zygomaticus and temporalis muscles.
