The Levator Labii Superioris Muscle is a muscle responsible for elevating the upper lip and plays an important role in facial expressions. Also known as the quadratus labii superioris , it consists of three anatomical heads: the angular head (levator labii superioris alaeque nasi), the infraorbital head, and the zygomatic head (closely related to the zygomaticus minor).
Anatomy
Morphology and Connection Points
The Levator Labii Superioris Muscle is a multi-headed muscle responsible for facial expressions of the upper lip and is divided into three distinct anatomical parts: the angular head (levator labii superioris alaeque nasi), the infraorbital head, and the zygomatic head. The angular head originates from the frontal process of the maxilla; this part sends some of its fibers to the cartilage and skin of the nasal ala, while the other part joins the orbicularis oris on the lateral aspect of the upper lip. The infraorbital head originates just above the infraorbital foramen of the maxilla and partially from the zygomatic bone, inserting onto the middle portion of the upper lip adjacent to the levator anguli oris muscle. The zygomatic head originates from the surface of the zygomatic bone and courses medially and inferiorly to reach the upper lip. This multi-headed structure contributes to the formation of diverse facial expressions, making the muscle functionally flexible. The Levator Labii Superioris Muscle has topographic and functional connections with other facial muscles such as the orbicularis oris, levator anguli oris, and zygomaticus minor.
Embryological Origin and Classification
The Levator Labii Superioris Muscle belongs to the group of facial expression muscles and originates embryologically from the second pharyngeal arch. Like the muscles in the facial region, this muscle is formed by the differential migration of mesodermal cells, resulting in its multi-headed anatomical structure. This muscle is classified as part of the "levator group" among the muscles of expression and cooperates particularly with the muscles controlling movements of the upper lip and the nasal area. The anatomical regions from which its different heads originate reflect the complexity of facial development and the versatility of this muscle. The muscle's multi-headedness provides a dynamic structure that adapts to the changing expressions of the face.
Nerve Innervation and Vascular Supply
The Levator Labii Superioris Muscle receives its motor innervation from the zygomatic and buccal branches of the facial nerve (CN VII). These branches reach different anatomical regions of the muscle, enabling coordinated muscle contraction. This neural control enables precise control of facial movements, particularly in the upper facial region. Vascularly, the muscle receives its nutrients from branches of the facial artery (a. facialis) and the infraorbital artery. These arteries carry adequate oxygen and nutrients to all parts of the muscle. Careful evaluation of these vascular-nerve structures in aesthetic procedures is crucial to prevent complications.
Function and Clinical Relationships
The Levator Labii Superioris Muscle plays a key role in facial expressions by elevating the upper lip upward and slightly outward. It contributes to expressions such as nose curling (disgust), crying, wry smiles, or pain. It works synergistically with the levator anguli oris muscle and antagonistically with the depressor labii inferioris muscle. This balance ensures harmony of expression between the upper and lower facial regions. The levator labii superioris muscle serves as a key control point, particularly in speech and emotional expressions, where the upper lip plays an active role. The levator labii superioris muscle plays a crucial role in facilitating facial expressions and lip lift in the upper face. In cases of facial paralysis, or facial paralysis, the dysfunction of this muscle can lead to symptoms such as drooping of the upper lip, asymmetry during smiling, and decreased facial expression, which can negatively impact an individual's social interactions and emotional expression. Botulinum toxin injections for aesthetic purposes may be preferred for reducing nasolabial folds, which become prominent due to excessive contraction of this muscle. However, the injection dose and site of administration should be carefully determined, as excessive toxin administration may lead to weakness in upper lip movement. Among congenital structural anomalies, inadequate development or complete absence of the levator labii superioris muscle is also rarely observed. Such anomalies can manifest as congenital facial asymmetry, and early evaluation, especially in childhood, is crucial for both aesthetic and functional surgical planning.
