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The scapula, or shoulder blade, is a sturdy, flat, triangular bone that sits above the rib cage in the upper back. It creates the shoulder joint where it meets with the head of the humerus, the bone of the upper arm. The scapula can move in six directions, and each movement is produced by specific, primary muscles. The trapezius, a large, superficial back muscle, is one of the muscles that depress the scapula. The serratus anterior, pectoralis major, and pectoralis minor muscles can also actively depress the scapula.
| Characteristics | Values |
|---|---|
| Muscles that depress the scapula | Trapezius, Latissimus Dorsi, Serratus Anterior, Pectoralis Major and Minor, Levator Scapulae, and Rhomboids |
| Trapezius Muscle Function | Stabilize and move the scapula, elevate, depress, retract, and rotate the scapula and arm |
| Trapezius Muscle Description | Large, superficial back muscle, triangular, broad, and thin |
| Serratus Anterior Muscle Function | Prime mover in scapular protraction and scapular upward rotation, scapular stabiliser |
| Serratus Anterior Muscle Description | Very thin, fan-shaped, covers the side of the ribcage, lies deep under the scapula and pectoral muscles |
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What You'll Learn
The trapezius muscle
The upper trapezius fibres work in conjunction with the levator scapulae muscle to elevate the scapula at the scapulothoracic joint. They also enable neck extension and contribute to maintaining the level of the shoulders against gravity, such as when carrying a weight in the hand. The upper fibres can also elevate and upwardly rotate the scapula.
The middle trapezius fibres adduct the scapula, drawing the two scapulae together. They also medially retract the scapula, contributing to scapular stability.
The lower trapezius fibres depress the scapula and assist the upper fibres in upwardly rotating it. This downward rotation of the scapula is essential for throwing objects and is achieved in collaboration with the latissimus dorsi and other muscles. The lower trapezius fibres also rotate the scapulae medially.
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The rhomboid major and minor
The rhomboid major arises from the spinous processes of the T2 to T5 vertebrae and attaches to the medial border of the scapula, below the spine. It is an extrinsic muscle of the shoulder, located deep to the trapezius and inferior to the rhomboid minor. The rhomboid minor, on the other hand, is typically smaller and originates from the nuchal ligaments and the spinous processes of the C7 and T1 vertebrae, inserting above the spine of the scapula at its medial border.
Both the rhomboid major and minor receive their innervation from the dorsal scapular nerve (C4-C5), which is crucial for the coordinated actions required for scapular stability and control. The dorsal scapular nerve also innervates other muscles associated with the scapula, including the trapezius and levator scapulae. The vascular supply to the rhomboids is provided by the dorsal scapular artery, ensuring the delivery of oxygen and nutrients necessary for their function.
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The levator scapulae
The main function of the levator scapulae is to elevate the scapula and tilt the glenoid cavity inferiorly by rotating the scapula downward. When the scapula is fixed, contraction of the levator scapulae leads to the lateral flexion of the cervical vertebral column to the side and stabilizes the vertebral column during rotation. If the cervical spine is fixed, the levator scapulae muscle helps in elevating and rotating the scapula such that the lateral angle moves inferiorly (i.e., rotates the point of the shoulder down). When the scapula is stabilized, contraction of this muscle laterally flexes and rotates the neck to the same side. Bilateral contraction helps in the extension of the cervical spine.
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The serratus anterior
The vascular supply to the serratus anterior comes from the superior and lateral thoracic arteries (branches of the axillary artery) as well as branches from the thoracodorsal artery (a branch of the subscapular artery). The innervation of the serratus anterior is supplied by the long thoracic nerve (C5-7), a branch of the brachial plexus.
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The latissimus dorsi
The muscle is responsible for several functions, including extension, adduction, transverse extension or horizontal abduction, flexion from an extended position, and internal rotation of the shoulder joint. It also plays a role in the extension and lateral flexion of the lumbar spine. The latissimus dorsi is a climbing muscle, and it can raise the trunk upwards when the arms are fixed above the head. This muscle is essential in activities like rowing, swimming (especially the downstroke), and chopping.
In terms of blood supply, the latissimus dorsi receives input from the thoracodorsal artery and the dorsal perforating branches of the inferior three posterior intercostal arteries and the superior three lumbar arteries. The lymphatic drainage of this muscle follows the typical pattern, with superficial and deep lymphatics draining into the posterior group of axillary lymph nodes.
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Frequently asked questions
The trapezius, latissimus dorsi, serratus anterior, pectoralis major and minor, and the levator scapulae and rhomboid muscles all depress the scapula.
The scapula, or shoulder blade, is the bone that sits above the rib cage in the upper back. It forms the posterior of the shoulder girdle and connects the clavicle to the humerus.
The trapezius is a large, triangular back muscle that assists in posture, allowing the spinal column to remain erect. It also helps with active movements like side bending, rotation of the head, elevating and depressing the shoulders, and internally rotating the arm.
