The latissimus dorsi muscle is a striated skeletal muscle of the secondary back musculature, which makes up the largest muscle in the human body. The tasks of the back muscle are adduction, internal rotation as well as retroversion of the arms. Damage to the thoracodorsal nerve can paralyze the muscle.
What is dre latissimus dorsi muscle?
The back muscles consist of autochthonous and secondary muscles. Secondary back muscles include various skeletal muscles, including the latissimus dorsi muscle. In the literal translation, the Latin designation means something like “broadest back muscle”. In German specialist literature, the muscle is sometimes referred to as the large back muscle. The muscle acts on the shoulder girdle from the dorsal direction and corresponds to a muscle located superficially on the back. In terms of area, the latissimus dorsi muscle is the largest skeletal muscle in the human body. Its structure extends along the entire length of the spine. In its course at the upper edge of the pelvis, parts of the muscle are covered by the trapezius muscle, whose antagonist it is. In the human body, four different parts belong to the muscular structure: the pars vertebralis, the pars costalis, the pars iliaca and the pars scapularis. The muscle is motorically nnervated by the thoracodorsal nerve, which originates from the pars infraclavicularis of the brachial plexus and thus from segments C6 to C8. Like all other skeletal muscles, the latissimus dorsi muscle bears a striated pattern and is therefore classified as a striated muscle.
Anatomy and structure
The striated muscles are composed of homogeneous functional units of small size known as sarcomeres. These sarcomeres are composed of the myofilaments myosin and actin, which proportionally overlap each other. The striated shape is due to light I bands of actin and dark A bands of myosin. The latissimus dorsi muscle originates at the trunk and extends from the sacrum and ilium through the spinous processes of the thoracic and lumbar vertebrae. The skeletal muscle originates widely and also includes as points of origin the supraspinous ligament, the fascia thoracolumbalis, the ninth to twelfth ribs the os sacrum and the crista iliaca at the os ilium. From the originating surfaces, the fibers extend cranially and laterally to attach to the intertubercular sulcus of the humerus in the immediate vicinity of the teres major muscle. Through the axilla, the skeletal muscle extends to the humerus, forming a characteristic pattern with the anterior sawtooth muscle. The thoracodorsal artery, thoracodorsal vein, and thoracodorsal nerve run along the inner surface of the muscular structure.
Function and Tasks
Skeletal muscles belong to the voluntary musculature. Thus, voluntary movements are their function. The latissimus dorsi muscle is involved in the backward rotation of the arm with the palms facing outward. This function has popularly given the muscle the name “apron truss muscle”. The skeletal muscle exerts its main action when the arm is raised. From this position, it can lower the arm and simultaneously move the trunk upward. This form of movement is relevant, for example, for sports exercises such as pull-ups. Together with the teres major muscle, the latissimus dorsi muscle forms the posterior crease of the axilla. The skeletal muscle is also a synergist in extension (stretching) and lateral flexion (sideways bending) of the lumbar spine. When the arm is fixed, the latissimus dorsi muscle also pulls the upper body toward the arm. For forms of movement such as climbing or rowing, it is a correspondingly important muscle. In addition, the skeletal muscle is counted among the respiratory support muscles. In this context, the contraction of its anterior fibers helps in pressed exhalation. The posterior fibers, on the other hand, help with forced inhalation. In some cases, the muscle is also referred to as the cough muscle, as the muscular structure aids in lung emptying during forceful breathing movements. As a skeletal muscle, the latissimus dorsi muscle is equipped with a so-called motor end plate, through which commands from the central nervous system reach it. These commands are transmitted in the form of bioelectrical excitation via the descending motor thoracodorsal nerve to the motor end plate and from there to the muscle fibers.
Diseases
Because of its flatness, the latissimus dorsi muscle plays a role as a tissue donor for plastic surgery. Flaps of skeletal muscle are commonly used as autologous grafts and aid reconstructive surgery in covering defects after more severe injuries and tumor removal. However, muscle can also gain pathologic relevance. This is the case, for example, with bursitis, an inflammation of the bursa subtendinea musculi latissimi dorsi. This bursa is located directly at the junction of the latissimus dorsi muscle and the teres major muscle. The phenomenon of bursitis in this region may be causally related to incorrect loading of the latissimus dorsi muscle. Infections are also a common cause. In most cases, bursitis in this area manifests itself as severe pain, which initially occurs due to strain, especially during forms of movement such as swimming, chopping wood or other contractions of the latissimus dorsi muscle. Like all other muscles of the body, the skeletal muscle can be affected by paralysis under certain circumstances. In particular, inflammatory, traumatic or compression-related damage to the supplying thoracodorsal nerve causes paresis of the structure. Symptomatically, the muscle narrows with persistent paralysis. The posterior axillary fold decreases. In addition, patients with paralysis of the latissimus dorsi muscle usually have the inferior angulus of the scapula protruding. Depending on the severity of the nerve injury, affected individuals may have difficulty pushing the arm downward anteriorly against resistance.
