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The back muscles are divided into two categories: extrinsic and intrinsic. The extrinsic muscles include the trapezius, latissimus dorsi, rhomboid major and minor, levator scapulae, and serratus posterior superior and inferior muscles. These muscles originate from the trunk and attach to the bones of the shoulder, such as the clavicle, scapula, and humerus. They are responsible for moving the upper extremity by controlling the movement of the scapula and humerus, enabling actions like reaching, lifting, pulling, and pushing. The trapezius, for example, assists in lifting the scapular bone, while the latissimus dorsi helps pull the torso superiorly and anteriorly when the arm is raised above the head. Understanding the anatomy of the extrinsic back muscles is crucial for precise instrument placement during surgical procedures.
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What You'll Learn
The extrinsic muscles of the shoulder
The two superficial extrinsic muscles are the trapezius and the latissimus dorsi. The trapezius is a broad, flat, and triangular muscle, forming a trapezoid shape on each side. It originates from the skull, nuchal ligament, and the spinous processes of C7-T12, with fibres attaching to the clavicle, acromion, and scapula spine. The upper fibres of the trapezius elevate the scapula and rotate it during abduction of the arm, the middle fibres retract the scapula, and the lower fibres pull the scapula inferiorly. The trapezius works with other muscles to move the arm and stabilise the shoulder.
The latissimus dorsi is the largest extrinsic back muscle, spanning the entire lateral side of the back, from the lower back to the upper arm. It originates from the spinous processes of T7-T12, the thoracodorsal fascia, the posterior iliac crest, and the proximal third of ribs 9 through 12. The fibres then attach to the floor of the humeral bicipital groove. The latissimus dorsi adducts, extends, and medially rotates the humerus, helping to pull the torso superiorly and anteriorly when the arm is raised above the head.
The deep extrinsic muscles include the levator scapulae and the two rhomboid muscles (major and minor). The levator scapulae is a small, strap-like muscle that begins in the neck and descends to attach to the scapula. It originates from the transverse processes of the C1-C4 vertebrae and attaches to the medial border of the scapula. The levator scapulae elevates the scapula and assists in rotating it. The rhomboid muscles originate from the spinous processes of the T2-T5 vertebrae and attach to the medial border of the scapula, with the rhomboid minor situated superiorly to the rhomboid major. These muscles retract and rotate the scapula, working together to ensure that the scapula is attached to the ribcage.
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The extrinsic muscles of the back
An extrinsic muscle is a muscle that originates in the torso and attaches to the bones of the shoulder. The extrinsic muscles of the back include the trapezius, latissimus dorsi, rhomboid major and minor, levator scapulae, and serratus posterior superior and inferior muscles. These muscles are responsible for moving the upper extremity by controlling the movement of the scapula and humerus, which are important bones in the shoulder region.
The trapezius is a broad, flat, and triangular muscle that forms a trapezoid shape on each side. It is the most superficial of all the back muscles and assists in moving the arm and stabilizing the shoulder. The upper fibres of the trapezius elevate the scapula, while the middle fibres retract it and the lower fibres pull it inferiorly.
The latissimus dorsi is the largest extrinsic back muscle, spanning the entire lateral side of the back. It originates from the lower part of the back and covers a wide area. The muscle fibres course superolaterally before attaching to the floor of the humeral bicipital groove. The latissimus dorsi adducts, extends, and medially rotates the humerus, and also helps pull the torso superiorly and anteriorly when the arm is raised above the head.
The levator scapulae is a thin, strap-like muscle that descends from the neck to the scapula. It assists in lifting the scapular bone and works with the trapezius to rotate the scapula superiorly, allowing the arm to reach above the head.
The rhomboid muscles consist of the rhomboid minor and rhomboid major. The rhomboid minor is the smaller of the two and is located superiorly, originating from the C7 and T1 vertebrae and attaching to the medial scapular border near the scapulothoracic joint. The rhomboid major originates from the T2 to T5 vertebrae and attaches just below the rhomboid minor. The rhomboid muscles retract and rotate the scapula, working together with the trapezius to stabilize the shoulders during motion.
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The trapezius muscle
Extrinsic muscles originate from the torso and attach to the bones of the shoulder (clavicle, scapula, or humerus). They are located in the back and are also known as the superficial back muscles. The trapezius muscle is one such extrinsic muscle.
- Moving the head, neck and upper back
- Maintaining and adjusting posture
- Turning the head to either side
- Twisting the torso
- Shrugging the shoulders or pulling them back
- Moving the shoulder when lifting the arm or throwing something
- Pushing, reaching forward, or pulling down
- Rowing or pulling motions
- Lifting the arm in all planes
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The rhomboid muscles
Extrinsic muscles originate from the torso and attach to the bones of the shoulder (clavicle, scapula, or humerus). They are located in the back and are also known as the superficial back muscles. The extrinsic muscles of the shoulder include the trapezius, the latissimus dorsi, and the levator scapulae.
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The levator scapulae
Extrinsic muscles originate from the torso and attach to the bones of the shoulder (clavicle, scapula, or humerus). They are located in the back and are also known as the superficial back muscles.
The main function of the levator scapulae is to elevate the scapula and retract the shoulder girdle at the scapulothoracic joint. It also helps in preventing the depression of the girdle when carrying heavy loads. It further participates in the stabilization of the scapula and the inferior rotation of the glenoid cavity. When acting on the cervical joints, unilateral contraction of the muscle produces ipsilateral flexion of the neck, while bilateral contraction contributes to extension of the neck.
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Frequently asked questions
Extrinsic muscles are those that originate in the torso and attach to the bones of the shoulder (clavicle, scapula, or humerus). They are located in the back and are also known as the superficial back muscles.
Examples of extrinsic muscles include the trapezius, latissimus dorsi, rhomboid major, rhomboid minor, and levator scapulae.
The principal function of extrinsic muscles is to move the upper extremity by controlling the movement of the scapula and humerus. They enable complex actions such as reaching, lifting, pulling, and pushing.
The back muscles are separated into extrinsic and intrinsic components based on their embryological origin and role in movement. Intrinsic muscles, which are deeper, are primarily responsible for attaching to and controlling the posture and movement of the spine.
