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You are watching: Muscular walls of the thorax and abdomen are composed of

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



The thoracic wall is comprised of 5 muscles: the exterior intercostal muscles, internal intercostal muscles, innermost intercostal muscles, subcostalis, and transversus thoracis. This muscles are generally responsible for an altering the volume of the thoracic cavity throughout respiration. Various other muscles that perform not comprise the thoracic wall, but connect to it incorporate the pectoralis significant and minor, subclavius, and serratus anterior (anteriorly) and the major costarum and serratus posterior superior and also inferior (posteriorly). The muscles of the anterior thorax provide movements come the arm and also shoulder while the muscle of the posterior thorax likewise help change thoracic volume during breathing and also reinforce the thoracic wall. The diaphragm is one more muscle in the thorax that serves together the main muscle of inspiration. It likewise makes increase the floor of the thorax, for this reason separating the contents of the chest native those the the abdomen. Various other minor accessory muscles that attach to the thorax incorporate the scalene muscles and the sternocleidomastoid muscle, both of i beg your pardon may additionally minimally aid in respiratory tract efforts.

Structure and Function

The muscles that make up the thorax wall include the 3 intercostal muscle (external, internal, and innermost), the subcostalis, and the transversus thoracis. Eleven bag of intercostal muscles are in each of the intercostal spaces, arranged from superficial come deep. The many superficial class is the external intercostal muscle, i beg your pardon originates native the inferior facet of the rib over and inserts ~ above the superior facet of the rib listed below in an inferomedial direction. These muscles expand from the rib tubercle posteriorly and also attach come the costochondral junction anteriorly whereby they proceed as slim connective organization aponeuroses known as the anterior (external) intercostal membrane.

During inspiration, the external intercostals contract and also raise the lateral component of the ribs, boosting the transverse diameter the the thorax in a bucket manage motion. The interior intercostal muscle creates the intermediary layer. These muscles originate native the lateral facet of the costal groove the the rib above and insert right into the superior aspect of the rib listed below in a direction perpendicular come the exterior intercostal muscles. This arrangement allows them to depress the ribs and also subsequently mitigate the thoracic volume throughout forced expiration. Further, these muscles prolong from the sternum anteriorly come the rib cage posteriorly whereby they proceed as the posterior (internal) intercostal membrane. The deepest layer of the thorax wall surface is made up of the innermost intercostal muscles. Castle originate from the medial element of the costal groove of the rib over and insert top top the internal aspect of the rib below. This muscles are lined internally by the endothoracic fascia, which appears just superficial come the parietal pleura the the lungs. They space thought to act with the interior intercostal muscle during forced expiration.<1><2>

In enhancement to the intercostal muscles, the subcostalis and the transversus thoracis also make increase the thoracic wall. The subcostalis exists in the very same layer together the innermost intercostal muscle and is existing in diversity in the reduced regions the the posterior thoracic wall. They originate indigenous the internal aspect of one of the reduced ribs and also insert onto the internal element of the 2nd or third rib below. The transversus thoracis additionally appears in the same an are at the innermost intercostal muscle. Lock originate native the lower posterior sternum, spread across the inner surface of the thoracic cage, and also inserts onto ribs 2 through 6. Both of this muscles aid in depressing the ribs throughout forced expiration.<2>

Muscles of the posterior thorax, such as the levatores costarum and serratus posterior superior and inferior, might also aid in respiration. The levatores costarum originates native the transverse processes of C7 come T11 and inserts ~ above the rib below. It minimally aids in inspiration via rib elevation. The serratus posterior exceptional attaches to ribs 2 v 5 and elevates them throughout inspiration conversely, the serratus posterior worse attaches the vertebrae come ribs 8 through 12 and depresses lock during forced expiration.<2> These muscles, in conjunction with the muscles of the thoracic wall, help alter the thoracic volume throughout respiration and also altogether reinforce the thoracic wall.

The significant muscle of inspiration, however, originates from the diaphragm. The diaphragm is fastened peripherally to the xiphoid procedure (sternal portion), the costal margin of the thoracic wall and lower sixth ribs (costal portion), and also the lumbar vertebrae (lumbar part). During inspiration, the muscle contracts and pulls down its main tendon inferiorly, therefore flattening the diaphragm - this activity increases the vertical diameter the the thorax and increases the an adverse thoracic pressure, which ultimately draws air right into the thoracic cavity. During expiration, the diaphragm relaxes and also elevates, forcing the air with the lung to it is in expelled from the body. Other accessory muscles that help inspiration include the scalene muscles (helps elevate the first and 2nd ribs) and sternocleidomastoid muscle (assists in increasing the sternum). Besides respiration, the diaphragm also functions to aid abdominal muscle straining and increase intra-abdominal press upon contraction throughout times of micturition, defecation, and even weightlifting.<2><3> 

Other muscles of the thorax are affiliated in top limb movement, which encompass the pectoralis significant and minor, subclavius, and serratus anterior muscles. The pectoralis major originates indigenous the medial fifty percent of the clavicle, anterior sternum, an initial seven costal cartilages, and also aponeurosis the the external oblique and also inserts ~ above the lateral lip intertubercular sulcus the the humerus. It features to flex, adduct, and also medially revolve the arm at the glenohumeral joint. That clavicular head reasons flexion of the expanded arm when its sternoclavicular head reasons extension that the flexed arm.<4> The pectoralis minor muscle originates native the anterior surfaces of ribs 3 come 5 and the deep fascia overlying the associated 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. That may additionally assist respiratory efforts as one accessory muscle by lifting the third, fourth, and also fifth ribs during inspiration.<2> The subclavius muscle originates in ~ the costochondral junction that the very first rib and also inserts at the subclavian groove of the clavicle. It features to stabilize the clavicle.

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The serratus anterior muscle originates on the superolateral surface of the first to eighth ribs or the very first to ninth ribs in ~ the lateral wall surface 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 viewed in punching, thus its colloquial nickname as the "boxer"s muscle," thus facilitating scapular rotation. The serratus anterior may likewise assist in inspiratory initiatives by elevating the ribs as soon as the shoulder girdle is in a addressed position.<6>