Dominic Stone
The human face has approximately 40 muscles, and the depressor labii inferioris is one of them. This muscle, sometimes referred to as the quadratus labii inferioris, is responsible for depressing the lower lip. It originates from the oblique line and mental tubercle of the mandible and inserts into the skin and muscle of the lower lip. The platysma muscle, which is not a head muscle, also plays a role in depressing the lower lip.
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What You'll Learn
Depressor labii inferioris pulls the lower lip down, creating a pout
The depressor labii inferioris is a muscle that originates from the body of the mandible and inserts into the skin and muscle of the lower lip. As its name, which translates to "depresses below the lip", suggests, its function is to depress or draw the lower lip downward. This muscle works together with the mentalis to create a pouty facial expression.
To feel the contraction of the depressor labii inferioris, place your finger about 1 inch (2.5 cm) below your lower lip and slightly to the side of the midline. Then, protrude your lower lip as if you are pouting. The mentalis, which originates from the mandible below the incisors, is also activated when you make a pouty face. It inserts into the skin of the chin and protrudes the lower lip, creating a wrinkle in the chin.
The depressor labii inferioris is a complex muscle that can be challenging to differentiate from the nearby depressor anguli oris, as both muscles are responsible for dropping and moving the corner of the mouth and lower lip laterally. The platysma, which is not a head muscle but plays a role in facial expression, also helps to depress the mandible and pull the lower lip back and down.
The orbicularis oris is another muscle involved in lip movement. It is a circular muscle located in the mouth that can contract to decrease the size of the oral opening. It is a complex muscle with fibres running in many directions, and it surrounds the opening to the oral cavity. Adequate function of the orbicularis oris is necessary for closing the mouth, chewing, and creating an oral seal.
The depressor labii inferioris, along with other muscles of facial expression, can become tight if the same facial expression is frequently made, requiring repeated contraction. This can lead to notching as a common outcome of surgical interventions on the lips.
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Mentalis protrudes the lower lip and wrinkles the chin
The mentalis muscle is a facial muscle situated in the chin. It is sometimes referred to as the
The mentalis muscle causes a weak upward-inward movement of the soft tissue complex of the chin, raising the central portion of the lower lip. This movement adjusts the shape of the lips for drinking and expressing emotions such as sorrow, contempt, and doubt.
The mentalis muscle is part of the buccolabial group of facial expression muscles, which also includes the depressor labii inferioris. Together, these muscles help form expressions such as a pout. The depressor labii inferioris originates from the mandible and inserts into the skin and muscle of the lower lip, drawing it downward.
The platysma is another muscle involved in depressing the lower lip. Although not a head muscle, it plays a role in facial expressions. It originates from the fascia of the chest over the pectorals and deltoids, and inserts into the lower margin of the mandible and the skin at the corner of the mouth.
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Depressor anguli oris drops the corner of the mouth
The depressor anguli oris muscle is responsible for dropping the corner of the mouth. It is one of the muscles that lower and evert the lower lip, along with the depressor labii inferioris and mentalis muscles. The depressor anguli oris is a small, thin muscle that is located in the lower part of the face. It originates from the mandible, the bone that forms the jaw, and inserts into the skin and muscle at the corner of the mouth.
This muscle is important for a range of facial expressions and movements, including frowning and shaping the lips during drinking. It works in conjunction with other muscles to create a variety of expressions. For example, when a person frowns, they contract the depressor anguli oris, pulling the corner of the mouth downward. At the same time, they may also engage the orbicularis oris muscle, which surrounds the opening of the oral cavity, to close the lips.
The depressor anguli oris is a complex muscle with intricate functions. It is challenging to differentiate it from the nearby depressor labii inferioris muscle, as both are involved in dropping and laterally moving the corner of the mouth. However, the depressor anguli oris is distinct in its specific role in depressing the angle of the mouth, contributing to the variety of smile shapes observed in humans.
The depressor anguli oris is supplied by the marginal mandibular branch of the facial nerve, which controls the majority of muscles responsible for lip depression. Damage to this nerve branch can lead to lower lip palsy, resulting in an asymmetrical appearance of the lip that affects smiling, speech, and articulation. Thus, the depressor anguli oris plays a crucial role in facial expression and communication.
In summary, the depressor anguli oris muscle is responsible for dropping the corner of the mouth, contributing to a range of facial expressions. It works in conjunction with other muscles and is controlled by the marginal mandibular branch of the facial nerve. This muscle is an essential component of human facial expressions and communication.
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Platysma pulls the lower lip back and down
The platysma muscle, also known as platysma, is a broad and flat superficial muscle in the human neck. It arises from the fascia covering the upper parts of the pectoralis major muscle and deltoid muscle. Its fibres cross the clavicle and proceed obliquely upward and medially along the side of the neck. The platysma plays a role in facial expressions and certain movements of the lower face and neck.
The platysma helps depress the mandible and pull the lower lip back and down. Men and women exercise this muscle when shaving their necks. The origin of the platysma is the fascia of the chest over the pectorals and deltoids, and its insertion is the lower margin of the mandible, as well as the skin and muscle at the corner of the mouth. The facial part of the platysma is primarily innervated by the marginal mandibular branch of the facial nerve, while the submandibular platysma is innervated by the “first” cervical branches, which terminate at the mandibular origin of the depressor labii inferioris.
The platysma is involved in depressing the lower lip and receives its innervation via the cervical branch of the facial nerve. It draws down the lower lip and angle of the mouth in a frown, aiding in expressions of sadness. The platysma also plays a role in widening the aperture of the corners of the mouth, as in an expression of horror. However, it is important to note that the platysma plays only a minor role in depressing the lower lip, with the primary muscles responsible for this function being the depressor anguli oris muscle and the depressor labii inferioris muscle.
The platysma is a significant focus in cosmetic procedures aimed at rejuvenating the lower face and neck. Procedures such as neck lifts or lower face lifts often involve addressing the platysma to smooth out the neck and improve the jawline. Techniques may include tightening or resecting part of the muscle. As people age, the platysma can become more prominent, contributing to visible neck bands or wrinkles due to the loss of skin elasticity and weakening of the muscle.
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Damage to the depressor labii inferioris leads to lower lip palsy
The depressor labii inferioris is a facial muscle that originates from the outer surface of the mandible (lower jaw) and stretches upward to attach to the skin of the lower lip. It is responsible for depressing or pulling the lower lip downward and forward when contracted. This muscle is also involved in forming facial expressions associated with sadness, melancholy, and doubt.
Damage to the depressor labii inferioris can lead to lower lip palsy, resulting in an asymmetrical and rolled-in appearance of the lip. This condition affects smile aesthetics, speech, and articulation. Symptoms of depressor labii inferioris dysfunction may include decreased movement of the lower lip, muscle pain in the chin, muscle weakness, loss of muscle control, bleeding, swelling, or bruising. In some cases, individuals may experience difficulty with eating, drinking, and speaking.
Bell's palsy, a common source of facial paralysis, can affect the depressor labii inferioris by damaging the facial nerve. This condition may cause weakness or total paralysis of the muscle, impacting an individual's ability to make facial expressions. Other causes of facial nerve paralysis that can affect the depressor labii inferioris include head trauma, injuries from surgery, and tumors pressing on the facial nerve.
Treatment options for lower lip palsy due to depressor labii inferioris damage may include surgical resection of the muscle, as well as non-surgical approaches such as lidocaine and chemodenervation. In some cases, physical therapy or exercises targeting the muscle may be recommended to improve lower lip symmetry and movement.
To identify damage to the depressor labii inferioris, one can perform a simple test by gently placing a finger under the lower lip, slightly lateral to the midline of the lips. Then, move the lower lip down and to the side as if baring the teeth. If the depressor labii inferioris is intact, one should feel the muscle contracting beneath the fingertips during this movement.
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Frequently asked questions
The Depressor Labii Inferioris muscle depresses the lower lip.
The Depressor Labii Inferioris is located below the bottom lip, near the chin.
This muscle assists in making a pout of the lips by pulling the flesh and skin of the lower lip down, baring the lower teeth.
Place your finger under the lower lip and slightly to the side of the midline of your lips. Move your lower lip down and to the side as if baring your teeth, and you should feel the muscle contracting.
Symptoms can include decreased movement of the lower lip, muscle pain in the chin, muscle weakness, loss of muscle control, bleeding, swelling, or bruising.
