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You are watching: This superficial muscle covers a large part of the posterior thorax.

StatPearls . Sweetheart Island (FL): StatPearls Publishing; 2021 Jan-.


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Introduction

The thoracic wall is made up of five muscles: the external intercostal muscles, interior intercostal muscles, innermost intercostal muscles, subcostalis, and transversus thoracis. These muscles are generally responsible for an altering the volume that the thoracic cavity throughout respiration. Various other muscles that perform not comprise the thoracic wall, but attach to it include the pectoralis major and minor, subclavius, and serratus anterior (anteriorly) and also the major costarum and also serratus posterior superior and also inferior (posteriorly). The muscle of the anterior thorax administer movements to the arm and shoulder while the muscle of the posterior thorax likewise help change thoracic volume during breathing and reinforce the thoracic wall. The diaphragm is another muscle in the thorax that serves together the main muscle of inspiration. It likewise makes increase the floor the the thorax, hence separating the materials of the chest from those that the abdomen. Various other minor accessory muscle that attach come the thorax encompass the scalene muscles and the sternocleidomastoid muscle, both of which may additionally minimally help in respiratory efforts.


Structure and also Function

The muscles that comprise the thorax wall surface include the three intercostal muscle (external, internal, and also innermost), the subcostalis, and the transversus thoracis. Eleven pairs of intercostal muscles room in every of the intercostal spaces, i ordered it from superficial come deep. The most superficial class is the external intercostal muscle, which originates native the inferior facet of the rib above and inserts ~ above the superior facet of the rib listed below in one inferomedial direction. These muscles extend from the rib tubercle posteriorly and also attach come the costochondral junction anteriorly whereby they continue as thin connective organization aponeuroses well-known as the anterior (external) intercostal membrane.

During inspiration, the outside intercostals contract and raise the lateral part of the ribs, raising the transverse diameter that the thorax in a bucket manage motion. The inner intercostal muscle forms the intermediate layer. These muscles originate from the lateral aspect of the costal groove that the rib above and insert right into the superior element of the rib below in a direction perpendicular come the exterior intercostal muscles. This arrangement permits them to boring the ribs and subsequently minimize the thoracic volume throughout forced expiration. Further, this muscles expand from the sternum anteriorly come the rib cage posteriorly where they proceed as the posterior (internal) intercostal membrane. The deepest great of the thorax wall is consisted of of the innermost intercostal muscles. Castle originate from the medial element of the costal groove that the rib over and insert top top the internal element of the rib below. This muscles are lined inside by the endothoracic fascia, which appears just superficial come the parietal pleura that the lungs. They space thought come act through the inner intercostal muscle throughout forced expiration.<1><2>

In addition to the intercostal muscles, the subcostalis and also the transversus thoracis likewise make increase the thoracic wall. The subcostalis exists in the very same layer together the innermost intercostal muscle and is present in variety in the lower regions of the posterior thoracic wall. Lock originate from the internal facet of among the reduced ribs and insert top top the internal element of the 2nd or third rib below. The transversus thoracis likewise appears in the same room at the innermost intercostal muscle. Castle originate from the lower posterior sternum, spread across the inner surface of the thoracic cage, and inserts ~ above ribs 2 through 6. Both of this muscles help in depressing the ribs during forced expiration.<2>

Muscles that the posterior thorax, such together the levatores costarum and serratus posterior superior and also inferior, might also aid in respiration. The levatores costarum originates native the transverse procedures of C7 to T11 and inserts top top the rib below. It minimally aids in catalyst via rib elevation. The serratus posterior remarkable attaches come ribs 2 with 5 and also elevates them throughout inspiration vice versa, the serratus posterior worse attaches the vertebrae to ribs 8 through 12 and also depresses castle during forced expiration.<2> These muscles, in conjunction through the muscle of the thoracic wall, assist alter the thoracic volume throughout respiration and also altogether reinforce the thoracic wall.

The major muscle of inspiration, however, originates from the diaphragm. The diaphragm is fastened peripherally come the xiphoid procedure (sternal portion), the costal margin the the thoracic wall and lower sixth ribs (costal portion), and also the lumbar vertebrae (lumbar part). Throughout inspiration, the muscle contracts and pulls down its central tendon inferiorly, thus flattening the diaphragm - this action increases the vertical diameter that the thorax and also increases the negative thoracic pressure, which ultimately draws air right into the thoracic cavity. During expiration, the diaphragm relaxes and also elevates, forcing the air v the lungs to it is in expelled native the body. Other accessory muscles that assist inspiration include the scalene muscles (helps elevate the very first and 2nd ribs) and sternocleidomastoid muscle (assists in elevating the sternum). Besides respiration, the diaphragm additionally functions to aid abdominal straining and also increase intra-abdominal push upon contraction throughout times that micturition, defecation, and also even weightlifting.<2><3> 

Other muscle of the thorax are involved in top limb movement, which include the pectoralis significant and minor, subclavius, and serratus anterior muscles. The pectoralis major originates indigenous the medial fifty percent of the clavicle, anterior sternum, very first seven costal cartilages, and aponeurosis of the outside oblique and also inserts top top the lateral lip intertubercular sulcus the the humerus. It attributes to flex, adduct, and medially turn the arm at the glenohumeral joint. That clavicular head reasons flexion that the prolonged arm while its sternoclavicular head causes extension the the flexed arm.<4> The pectoralis minor muscle originates from the anterior surface of ribs 3 to 5 and also the deep fascia overlying the connected intercostal spaces and inserts ~ above the coracoid procedure of the scapula. It functions mainly to depress the tip of the shoulder and also protract the scapula. The may also assist respiratory efforts as one accessory muscle by lifting the third, fourth, and fifth ribs throughout inspiration.<2> The subclavius muscle originates at the costochondral junction the the an initial rib and inserts in ~ the subclavian groove the the clavicle. It attributes to stabilize the clavicle.

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The serratus anterior muscle originates top top the superolateral surface of the very first to eighth ribs or the an initial to ninth ribs in ~ the lateral wall of the thorax and also inserts follow me the superior angle, medial border, and also inferior edge of the scapula. It mainly attributes to protract the scapula as checked out in punching, for this reason its colloquial nickname as the "boxer"s muscle," thus facilitating scapular rotation. The serratus anterior may additionally assist in inspiratory initiatives by elevating the ribs when the shoulder girdle is in a fixed position.<6>