Logan Steele
The human face has about 20 facial muscles that are essential for chewing and making facial expressions. One of the most well-known facial muscles is the risorius muscle, commonly known as the smiling muscle. The risorius muscle is a narrow bundle of muscle fibres that originates at the fascia of the lateral cheek and inserts onto the skin of the angle of the mouth. Its primary function is to aid in facial expression by pulling the corners of the mouth upwards and outwards, resulting in a smile. In addition to the risorius, other muscles involved in producing a smile include the levator anguli oris, zygomaticus major, zygomaticus minor, and levator labii superioris.
| Characteristics | Values |
|---|---|
| Name of the smile muscle | Risorius |
| Location | Originates from the fascia of the lateral cheek over the parotid gland and superficial masseter and platysma muscles, and inserts onto the skin of the angle of the mouth |
| Structure | A narrow bundle of muscle fibers that becomes narrower towards its insertion |
| Innervation | Facial nerve |
| Arterial supply | Facial artery and transverse facial artery |
| Venous drainage | Facial vein and transverse facial vein |
| Lymph drainage | Submandibular and mandibular lymph nodes |
| Function | Pulls the corners of the mouth laterally and upward to produce a smile |
| Associated muscles | Levator anguli oris, zygomaticus major, zygomaticus minor, levator labii superioris |
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What You'll Learn
The risorius muscle is commonly known as the smiling muscle
The risorius muscle is commonly known as the "smiling muscle". It is a narrow bundle of muscle fibres that originates at the fascia of the lateral cheek and narrows as it moves over the parotid gland and superficial masseter and platysma muscles, inserting onto the skin of the angle of the mouth. The risorius muscle is located within the deep portion of the superficial musculoaponeurotic system (SMAS), a fibrous network containing various facial muscles.
The primary function of the risorius muscle is to aid in facial expressions by pulling the corners of the mouth upward and outward through its contraction. This movement, in conjunction with other facial muscles, helps create a smile, a frown, or a myriad of other expressions. The risorius muscle works alongside the levator anguli oris, zygomaticus major, zygomaticus minor, and the levator labii superioris muscles to form a smile.
The risorius muscle is unique to hominines, including African great apes and humans, evolving from a common ancestor. It is not present in all people. The muscle receives its arterial blood supply from the facial artery and the transverse facial artery, which are branches of the external carotid artery.
The risorius muscle is innervated by the facial nerve, which sends signals to the brain when the muscle is activated during smiling. This activation triggers the release of endorphins into the bloodstream, influencing emotional states and stress levels.
In summary, the risorius muscle, commonly known as the "smiling muscle," plays a crucial role in producing smiles by pulling the corners of the mouth upward and outward. It is unique to hominines and contributes to the complex emotional expressions that distinguish our species.
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Levator anguli oris elevates the angles of the lips
The levator anguli oris (LAO) is a muscle of facial expression that is responsible for elevating the angles of the lips. It is located above the angles of the lips and is part of a large group of muscles called the buccolabial group, which control the shape, position, and movement of the lips.
The LAO works in conjunction with other muscles such as the zygomaticus major and minor, levator labii superioris, and levator labii superioris alaeque nasi to produce a smile. It does this by raising the corners of the mouth, deepening the nasolabial folds, and providing an upper dental show. This muscle is not the most critical of the smile muscles, but its function is important as unilateral LAO paralysis can lead to noticeable smile asymmetry, impacting a person's quality of life.
The LAO is also significant in maintaining the oral commissure's resting position, which is why it is often targeted in midfacial rejuvenation procedures. It is also a component of interest during lip repositioning or reconstructive surgeries due to its muscular and closely associated mucosal component.
The LAO is a valuable landmark in determining volumizing injection locations for optimal aesthetics and safety. It plays a crucial role in producing a natural-appearing, dentate, or "Duchenne" smile, which is essential for human social connection and expressing emotion.
By relaxing the depressor anguli oris (DAO) muscle, which works to depress and pull down the corner of the mouth, the LAO can act unopposed and elevate the oral commissure, contributing to a more pronounced smile.
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Zygomaticus major elevates the angle of the mouth
The zygomaticus major muscle is a thin, paired facial muscle that extends diagonally from the zygomatic bone (cheekbone) to the angle of the mouth. It belongs to the buccolabial group of facial muscles, which form the structure and carry out the functions of the cheeks and lips.
The primary function of the zygomaticus major muscle is to elevate the angle of the mouth, or pull the mouth superolaterally. In coordination with other muscles, it facilitates speech and creates facial expressions. For example, when the zygomaticus major contracts, it pulls the angle of the mouth upwards and backwards, resulting in a smile. This movement is often accompanied by the risorius muscle, which pulls the corners of the mouth outward and upward. Together, these muscles contribute to laughing, earning them the nickname "the laughing muscles".
The zygomaticus major muscle originates from the lateral surface of the zygomatic bone, specifically from the superior margin of its temporal process. It inserts at the corner of the mouth, where it blends with other muscles such as the levator anguli oris, orbicularis oris, and deeper muscular structures. At the point of insertion, the muscle sometimes divides into two parts, forming two separate bundles. This split is known as the duplication or bifurcation of the zygomaticus major, and it can result in dimples when smiling.
The zygomaticus major muscle is innervated by branches of the facial nerve (cranial nerve VII), specifically the buccal branch and zygomatic branch. These nerves send signals to the brain when the muscles are activated, indicating that a smile is being formed. This activation can have a positive impact on mood and stress levels, as it triggers the release of endorphins into the bloodstream.
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Zygomaticus minor extends diagonally towards the lips
The human face has about 20 facial muscles, which are essential for chewing and making facial expressions. The risorius muscle, commonly known as the "smiling muscle", is one of the muscles involved in smiling. However, there are several other muscles that work together to produce a smile.
The zygomaticus minor is one such muscle that contributes to smiling. Similarly to its major counterpart, the zygomaticus minor arises from the lateral surface of the zygomatic bone and extends diagonally towards the lips. It inserts on the skin of the upper lip, medial to the zygomaticus major. The zygomaticus minor acts in harmony with other tractors of the upper lip to elevate and evert the upper lip, contributing to a variety of facial expressions such as smiling, frowning, or grimacing.
The zygomaticus minor is innervated by the zygomatic and buccal branches of the facial nerve (CN VII), while its vascular supply comes from the superior labial branch of the facial artery. The facial nerve plays a crucial role in smiling by sending signals to the brain that you are smiling, leading to the release of endorphins into the bloodstream.
The zygomaticus minor is part of the buccolabial group of facial muscles, which also includes the zygomaticus major, levator labii superioris, levator labii superioris alaeque nasi, 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 carry out the functions of the cheeks and lips, enabling various facial expressions and speech.
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Levator labii superioris enables smiling or showing disgust
The human face has about 20 facial muscles, which are essential for chewing and making facial expressions. One of these muscles is the Levator labii superioris, which enables us to smile or show disgust.
The Levator labii superioris is a muscle that pulls the upper lip up to display teeth and sometimes the gums. It is also known as the "gummy smile" target treatment muscle. It originates on the upper portion of the maxilla and inserts into the alar cartilage and levator labii superiors. It starts on the sides of the nose and runs down the sides to the upper medial to the lateral portion of the lip.
The Levator labii superioris is also the central component of the characteristic facial expression of disgust. When the muscle is activated, the nose wrinkles. Research has shown that inducing disgust, but not anger, increases psychophysiological responses to moral themes.
Smiling is not just a facial expression but also has a positive impact on our mental health. Even if you're not happy, activating the muscles associated with smiling can fool your brain into thinking you are. This releases endorphins into the bloodstream, which act as the body's natural painkillers.
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Frequently asked questions
The risorius muscle is commonly known as the "smiling muscle" as its main function involves pulling the corners of the mouth to produce a smile.
Yes, the risorius works in conjunction with other facial muscles to produce a smile. These include the levator anguli oris, zygomaticus major, zygomaticus minor, and the levator labii superioris.
The risorius muscle is a narrow bundle of muscle fibres that originates near the cheek and extends to the skin at the corner of the mouth. It pulls the corners of the mouth laterally and upward to form a smile or a frown.
