Abduction anatomy3/13/2023 It can also function to extend and laterally flex the neck if the scapula is kept in a fixed position. The trapezius functions to laterally rotate, elevate, and retract the scapula. The inferior fibers originate from the spinous processes of T4-T12 and converge near the scapula in the form of an aponeurosis. The middle fibers also originate from the spinous process of C7, as well as the spinous processes of T1-T3, and insert upon acromion and the spine of the scapula. The superior fibers of the trapezius originate from the medial third of the superior nuchal line, spinous process of C7, external occipital protuberance, and nuchal ligament they converge and insert on the posterior portion of the lateral third of the clavicle. The trapezius is a large, superficial muscle of the back that divides into three functional parts: descending (superior), middle, and ascending (inferior). It also serves as a stabilizer of the humeral head, especially in instances of load carrying. The deltoid is the primary muscle responsible for the abduction of the arm from 15 to 90 degrees. All heads of the deltoid come together to insert on the deltoid tuberosity of the humerus. The posterior head originates from the posterior border of the spine of the scapula. The lateral head originates from the superior surface of the acromion process. The anterior head originates from the anterior surface of the lateral third of the clavicle. The deltoid, aptly named after the Greek letter delta, is a triangular-shaped muscle found over the glenohumeral joint and is composed of three different heads: anterior, lateral, and posterior. Additionally, the supraspinatus contributes to shoulder joint stability by providing resistance to gravitational forces acting on the joint and maintaining contact between the head of the humerus and the glenoid fossa. Past 15 degrees, it assists the deltoid with the abduction of the arm up to 90 degrees. It is responsible for the initiation of arm abduction and is in control of the motion up to the first 15 degrees of abduction. The supraspinatus muscle originates from the supraspinous fossa of the scapula, passes under the acromion, and inserts on the superior facet of the greater tubercle of the humerus. The neural supply of the serratus anterior is the long thoracic nerve (C5-C7) which originates from the roots of the brachial plexus. C3 and C4 are responsible for proprioception of the trapezius. The neural supply of the trapezius is the spinal accessory nerve (C1-C5). The neural supply of the deltoid is via the axillary nerve (C5, C6) from the posterior cord of the brachial plexus. The neural supply of the supraspinatus is by the suprascapular nerve (C5, C6) from the upper trunk of the brachial plexus. The circumflex scapular artery is the blood supply to the serratus anterior. The transverse cervical artery provides vascular supply to the trapezius. The posterior circumflex humeral artery and the deltoid branch of the thoracoacromial artery are the vascular sources for the deltoid. The suprascapular artery delivers blood to the supraspinatus muscle. EmbryologyĪll muscle within the body, save for a few exceptions, is mesodermal in origin during the development of the embryo. The trapezius and serratus anterior coordinate with each other and the scapula to facilitate abduction of the arm upwards of 90 degrees. The deltoid controls abduction from 15 to 90 degrees. The supraspinatus is the primary muscle for the abduction of the arm to 15 degrees. Four different muscles control this action: supraspinatus, deltoid, trapezius, and serratus anterior. The ability to abduct the arm is a crucial contributor to the full range of motion of the arm. (The upper extremity action during a jumping jack can is exemplary of the full range of motion for arm abduction.) The primary muscles involved in the action of arm abduction include the supraspinatus, deltoid, trapezius, and serratus anterior. The abduction of the arm begins with the arm in a position parallel to the torso and hand in an inferior position, continues with the movement of the arm to a position perpendicular to the torso, and ends with the movement of the arm so that the humerus is raised above the shoulder joint and points straight upward. In the case of arm abduction, it is the movement of the arms away from the body within the plane of the torso (sagittal plane). In general terms, abduction in the anatomical sense is classified as the motion of a limb or appendage away from the midline of the body.
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