The levator labii superioris muscle is a striated muscle of the mimic musculature. The main function of the muscle is the upward movement of the upper lip. Damage to the facial nerve paralyzes the levator labii superioris muscle.
What is the levator labii superioris muscle?
Skeletal muscles are composed of striated muscle and are largely responsible for the motor function of the human skeleton. Most skeletal muscles have direct contact with the bones. The so-called cutaneous muscles are an exception. This group of muscles is only slightly developed in humans. Human skin muscles mainly include some muscles of the facial expression. One of these muscles is the lavator labii superioris muscle. As the Latin name suggests, this mimic muscle is the so-called upper lip lifter. Like all skin muscles, the lavator labii superioris muscle does not sit directly on the human skeleton. Skin muscles are much more located between the fascia and the skin. The mimic muscle is located in the anterior cheek area on the nasal slope and consists of a course of different fiber strands: the caput angulare, the caput infraorbitale and the caput zygomaticum. Different literature refers only to the caput infraorbitale as the lavator labii superioris muscle and treats the other fiber strands as independent muscle fibers.
Anatomy and structure
Transversely striated muscles such as the lavator labii superioris muscle are always composed of filaments of myosin and actin. These contractile filaments overlap at various locations and are also referred to as contractile muscle components. The levator labii superioris muscle is connected to the nervous system by the rami buccales and rami zygomatici of the VII cranial nerve (facial nerve). The caput angulare corresponds to the medial fibrous cords of the muscle and forms the levator labii superioris alaeque nasi muscle originating at the frontal process. The cord runs obliquely downward and becomes caudal to two fiber portions that attach to wing cartilage (cartilago alaris major) and nasal wing skin. Another fiber portion supplies the lateral upper lip and attaches to the orbicularis oris muscle. The middle portions of the upper lip elevator correspond to the caput infraorbitale and arise from the inferior orbital rim over the foramen infraorbitale. The fibers reach the upper lip muscles between the canine and caput angulare. The lateral portion of the upper lip elevator is the caput zygomaticum, which corresponds to the zygomaticus minor muscle and originates from the bony surface of the os zygomaticum as it courses to the medial upper lip.
Function and Tasks
The lavator labii superioris muscle is a skeletal muscle, but unlike other skeletal muscles, its functions are not in bone motion. Instead of bone motor activity, the muscle is responsible for the motor movements of the face, and for these reasons it is included in the mimic musculature. Facial expressions play a key role in human communication. Where verbal communication causes misunderstandings, a smile or a snort, for example, can provide clarity. Since facial expression is a natural basic form of human expression, facial expressions are understood from infancy. Contraction of the lavator labii superioris muscle pulls the upper lip upward. The upward pull of the upper lip can signal disgust, for example. This is especially true if the lower lip pushes forward at the same time. Visible wrinkles form between the corners of the mouth and the corners of the nose during the movement. Often the nose is wrinkled at the same time. The contraction of the lavator labii superioris muscle is triggered by the facial nerve, which is the seventh cranial nerve responsible for the motor connection of many facial muscles to the central nervous system. The nerve contains sensitive, parasympathetic, and sensory fiber qualities in addition to motor fibers. Therefore, the mimic function of the upper lip elevator muscle is more correctly referred to as the function of the neuromuscular complex of the facial nerve and the lavator labii superioris muscle. From mimic movements such as an upturned upper lip, attitudes and spontaneous emotions of the counterpart can often be read within a conversation that have never been expressed.
Diseases
Like any other muscle, the lavator labii superioris muscle can be affected by various muscular and neuromuscular diseases.One degenerative muscle disease, for example, is myopathy, which is associated with muscle weakness and tremor. This phenomenon can be triggered by various influences. In addition to genetic causes, poisoning can play a role, for example, in alcohol myopathy. To be distinguished from muscular weaknesses is paralysis of the lavator labii superioris muscle. Paralysis of the structure results from lesions of the facial nerve and does not usually occur as isolated paralysis. Usually, other facial muscles are affected in their function by the so-called facial paresis. The facial nerve can be damaged by different diseases. The damage can occur in both the peripheral and central areas of the cranial nerve. In addition to infectious diseases such as Lyme disease or zoster oticus, mechanical effects such as petrous bone fracture as well as tumors can be responsible for peripheral damage to the nerve. Central damage, on the other hand, results from cerebral hemorrhage, autoimmunologic and bacterial inflammation, and brain tumors such as cerebellopontine angle tumor. In addition to myopathies and peripheral as well as central paresis, the superior labii lavator muscle may be affected by inflammation as well as trauma. Inflammation of the muscle usually results from overuse or misuse. Trauma, in turn, can be the cause of a muscle fiber tear. Although both phenomena can ultimately affect any muscle, they occur rather rarely in the superior labius muscle. The reason for this is the low stress placed on the muscle in daily life.
