Dominic Stone
The human face has 20 main facial muscles, or craniofacial muscles, which are essential to chewing and making facial expressions. One of the most important muscles for smiling is the risorius, which pulls the angles of the mouth laterally and superiorly to produce a smile. The levator anguli oris, zygomaticus major, and zygomaticus minor muscles also work together with the risorius to elevate the angles of the lips and produce a smile. Even fake smiling can have positive effects on your emotional state, as it can trick your brain into thinking you're happy and release endorphins, the body's natural painkillers.
| Characteristics | Values |
|---|---|
| Name of the smiling muscle | Risorius |
| Location | Mouth |
| Function | Pulling the angles of the mouth laterally and superiorly to produce a smile |
| Other muscles involved in smiling | Levator anguli oris, zygomaticus major, zygomaticus minor, depressor anguli oris, orbicularis oculi |
| Number of facial muscles | 20 |
| Facial muscles functions | Chewing, making facial expressions, controlling parts of the face |
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What You'll Learn
The risorius is the 'smiling muscle'
The human face has 20 main facial muscles, which are essential to chewing and making facial expressions. One of these muscles is the risorius, which is commonly known as the "smiling muscle". Its main function is to pull the angles of the mouth laterally and superiorly to produce a smile.
The risorius is one of the 11 muscles that form the buccolabial group of muscles, also known as the muscles of the mouth. These muscles form a functional compound that controls the shape and movements of the mouth and lips. The risorius works together with other muscles, such as the levator anguli oris, the zygomaticus major, and the zygomaticus minor, to elevate the angles of the lips and create a smile.
The zygomaticus major, for example, is a thin 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, a fibromuscular hub located at the angles of the mouth, by interlacing with several other facial muscles. The function of the zygomaticus major is to elevate and evert the angle of the mouth superolaterally, thereby producing a smile in synergy with other muscles, including the risorius.
The levator anguli oris is another muscle that contributes to smile formation. It is a slender, sheet-like muscle that arises from the canine fossa of the maxilla and extends towards the angle of the mouth. Its main function is to elevate the angles of the lips, working together with the risorius and other muscles.
The muscles involved in smiling are innervated by the various branches of the facial nerve (VII). When these muscles are activated, signals are sent to the brain indicating that you are smiling. This activation can even occur when the smile is fake, and it can still have an impact on your emotional state. As the muscles of a smile are engaged, the brain can be fooled into thinking you are happy, leading to the release of endorphins, the body's natural painkillers and opiates.
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The zygomaticus major and minor
The human face has 20 main facial muscles, or craniofacial muscles, which are essential to chewing and making facial expressions. The zygomaticus major and minor are two of these muscles, which are specifically responsible for forming a smile.
The zygomaticus major is a thin 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, a fibromuscular hub located at the angles of the mouth, by interlacing with several other facial muscles. The zygomaticus major is innervated by the zygomatic and buccal branches of the facial nerve (CN VII). Its function involves elevating and turning out the angle of the mouth, thereby producing a smile in synergy with other muscles.
The zygomaticus minor, similar to the zygomaticus major, also arises from the lateral surface of the zygomatic bone but extends diagonally towards the lips. It inserts into the skin of the upper lip, medial to the zygomaticus major. The zygomaticus minor works together with its major counterpart to elevate the lips and create a smile.
The act of smiling has been found to have numerous benefits for our health and well-being. A study at the University of Kansas found that participants who used chopsticks to shape their mouths into smiles had lower heart rates and stress levels compared to those faking frowns. Interestingly, even if one is not genuinely happy, activating the muscles associated with smiling can trick the brain into feeling happiness. This phenomenon is supported by the release of endorphins, the body's natural painkillers, which are secreted during times of excitement, love, and other positive emotional states.
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The levator labii superioris
The LLS is part of the buccolabial group of muscles, which work together to control the shape, posture, and movements of the lips. It elevates and everts the upper lip, exposing the maxillary teeth and creating facial expressions such as smiling, smugness, contempt, and disdain. The LLS also broadens the nostril by elevating the nasal ala and upper lip, pulling the alar facial crease and skin outward and upward.
The LLS is innervated by the zygomatic and buccal branches of the facial nerve (CN VII) and receives its vascular supply from the facial artery and the infraorbital branch of the maxillary artery. Impairment of the LLS can result from damage to the facial nerve or its zygomatic or buccal branches, with potential causes including trauma, Bell's palsy, Ramsay Hunt syndrome, Lyme disease, multiple sclerosis, poliomyelitis, Guillain-Barré syndrome, and SARS-CoV-2 infection.
Research has shown that activating the muscles associated with smiling, such as the LLS, can lead to lower heart rates and stress levels, even if the smile is not genuine. This is because the brain receives signals that the person is smiling, leading to the release of endorphins, which act as natural painkillers and contribute to feelings of happiness and calmness.
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The depressor anguli oris
The human face has 20 main facial muscles, or craniofacial muscles, which are essential to chewing and making facial expressions. One of these muscles is the depressor anguli oris. This muscle is responsible for pulling the angle of the mouth downward, enabling a facial expression associated with frowning. The depressor anguli oris is a facial muscle located in the mouth area. It is classified as the buccolabial facial muscle. The depressor anguli oris originates from the base of the mandible, specifically from the oblique line that runs in the posterior direction and from the mental tubercle. Both structures are located on the outer surface of the mandible.
The primary function of the depressor anguli oris is to pull the angle of the mouth downward. Contractions of this muscle participate in producing a facial expression of sadness. The depressor anguli oris is one of the "frowning muscles", along with muscles such as corrugator supercilii, procerus, and orbicularis oris. It is innervated by the marginal mandibular branch of the facial nerve (CN VII) and receives arterial blood supply mainly from the inferior labial branch of the facial artery. 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 contribute to an asymmetrical smile. This condition is rare and develops at or before birth (congenitally). Underdevelopment (hypoplasia) or complete absence (aplasia) of the depressor anguli oris can also result in an asymmetric smile. In some cases, resecting (cutting and removing) the depressor labii inferioris muscle may be necessary to correct an asymmetrical smile.
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The levator anguli oris
The primary function of the LAO is to elevate the corners of the mouth, working in tandem with other muscles like the zygomaticus major and minor, levator labii superioris, and levator labii superioris alaeque nasi. This collective action results in what we recognize as a smile, with the LAO specifically contributing to the curvature of the lips. The LAO also helps maintain the upper lip's resting tone and position, ensuring the mouth's corners are not turned downward when at rest.
The importance of the LAO extends beyond aesthetics. It is essential for proper speech and chewing (mastication). Any impairment or paralysis of this muscle can lead to noticeable smile asymmetry, impacting an individual's quality of life and overall facial aesthetics. Furthermore, the LAO is relevant in the medical field, particularly in facial reconstructive surgeries involving the upper lip and facial nerve. Its role in maintaining the oral commissure's resting position makes it a potential target for midfacial rejuvenation procedures and flaccid facial paralysis management.
The LAO is innervated by the buccal branches of the facial nerve (VII). When activated, these nerves send signals to the brain that you are smiling. This neural activity triggers the release of endorphins, the body's natural painkillers and opiates, into the bloodstream from the pituitary gland, the brain, and the spinal cord from the hypothalamus. This release of endorphins contributes to the emotional states associated with smiling, such as happiness and excitement.
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Frequently asked questions
The risorius is known as the "smiling muscle" as its main function is to pull the angles of the mouth to produce a smile.
The zygomaticus major, the zygomaticus minor, the levator labii superioris, and the levator anguli oris are all muscles that contribute to producing a smile.
Smiling is essential for verbal communication and can also help to reduce stress and increase happiness by releasing endorphins.
There are 20 main facial muscles, or craniofacial muscles, that are responsible for chewing and making facial expressions.
Damage to the facial nerve and problems with the facial muscles can be caused by autoimmune diseases, Bell's palsy, head and neck cancer, infections, and injuries to the head or face.
