The muscles of the shoulder are associated with movements of the upper limb and produce the characteristic shape of the shoulder. These muscles can be divided into two groups: extrinsic and intrinsic. Extrinsic muscles originate from the torso and attach to the bones of the shoulder (clavicle, scapula, or humerus) while intrinsic muscles originate from the scapula and/or clavicle and attach to the humerus. There are additional muscles that act on the shoulder joint, such as the muscles of the pectoral region and the upper arm. This article will look at the anatomy of the extrinsic muscles of the shoulder, including their attachments, innervation, and actions.
The extrinsic muscles of the shoulder are located in the back and are also known as the superficial back muscles. They are organized into two layers: a superficial layer and a deep layer.
The two superficial extrinsic muscles are the trapezius and latissimus dorsi.
The trapezius is a broad, flat, and triangular muscle. The muscles on each side form a trapezoid shape, and it is the most superficial of all the back muscles.
The latissimus dorsi originates from the lower part of the back, where it covers a wide area.
The three muscles in this group are the levator scapulae and the two rhomboids.
The levator scapulae is a small strap-like muscle. It begins in the neck and descends to attach to the scapula.
There are two rhomboid muscles – major and minor. The rhomboid minor is situated superiorly to the major.
The extrinsic muscles of the shoulder are responsible for a large range of actions, all of which are important for normal movement of the upper limb. It is important to understand the anatomy and function of these muscles in order to identify and treat musculoskeletal problems in the shoulder. The extrinsic muscles of the shoulder should be regularly examined and stretched to prevent injury and ensure optimal range of motion and strength in the upper limb.
The shoulder is composed of a variety of muscles, which can be divided into extrinsic and intrinsic groups. The extrinsic muscles act on the shoulder, while the intrinsic muscles act on both the shoulder and the scapula. The intrinsic group includes the levator scapulae, rhomboids, and serratus anterior muscles. It is important to understand the individual muscles of the shoulder, their attachments, innervations, and actions in order to properly treat shoulder injuries as well as for shoulder joint stability.
The extrinsic muscles are the main muscles acting on the shoulder. This group includes the trapezius, latissimus dorsi, and pectoralis major muscles.
The trapezius originates from the occipital bone, the ligamentum nuchae, and the spinous processes of C7-T12 vertebrae. The fibers converge into a tendon that attaches to the acromion process and the clavicle. The trapezius extends, rotates, and retracts the scapula, elevates the clavicle, and depresses the mandible. It also receives proprioceptor inputs from C3 and C4 spinal nerves. The trapezius is innervated by the spinal accessory nerve.
The latissimus dorsi is a broad muscle that covers a wide area of the lower back. It originates from the spinous processes of T7-T12 vertebrae, the iliac crest, the thoracolumbar fascia, and the inferior three ribs. The fibres converge into a tendon that attaches to the intertubercular sulcus of the humerus. It extends, adducts, and medially rotates the upper limb. The latissimus dorsi is innervated by the thoracodorsal nerve.
The pectoralis major originates from the medial half of the clavicle, the sternum, and the costal cartilages of ribs two to six. The fibres converge into a tendon that attaches to the humerus. It flexes, adducts, and medially rotates the upper limb. It is innervated by the medial and lateral pectoral nerves.
The intrinsic group of muscles includes the levator scapulae, the rhomboids, and the serratus anterior. These muscles are situated in the upper back, underneath the trapezius.
The levator scapulae originates from the transverse processes of the C1-C4 vertebrae and attaches to the medial border of the scapula. It elevates the scapula and is innervated by the dorsal scapular nerve.
The rhomboids consist of two muscles, the rhomboid major and the rhomboid minor. The rhomboid major originates from the spinous processes of T2-T5 vertebrae. It attaches to the medial border of the scapula, between the scapula spine and inferior angle. It retracts and rotates the scapula and is innervated by the dorsal scapular nerve. The rhomboid minor originates from the spinous processes of C7-T1 vertebrae and attaches to the medial border of the scapula, at the level of the spine of scapula. It also retracts and rotates the scapula and is innervated by the dorsal scapular nerve.
The serratus anterior originates from the ribs one to nine, at the lateral side of the thorax. It attaches to the medial border of the scapula from the superior angle to the inferior angle. It protracts the scapula and is innervated by the long thoracic nerve.
The shoulder consists of several muscles that can be divided into extrinsic and intrinsic groups. Each muscle has its own attachments, innervation, and actions. It is important to understand the individual muscles of the shoulder in order to properly diagnose and treat shoulder injuries and to ensure the stability of the shoulder joint.
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