Serratus anterior muscle

Last updated

Serratus anterior
Serratus anterior.png
Serratus anterior, showing origin from lower ribs (origin from upper ribs obscured by pectoralis major and other superficial muscles)
Gray1215.png
The left side of the thorax.
Details
Pronunciation /ˌsɪˈrtəsænˈtɪəriər/
Origin Fleshy slips from the outer surface of upper 8 or 9 ribs
Insertion Costal aspect of medial margin of the scapula
Artery Lateral thoracic artery, superior thoracic artery (upper part), thoracodorsal artery (lower part)
Nerve Long thoracic nerve (from roots of brachial plexus C5-C7)
Actions Protracts and stabilizes scapula, assists in upward rotation.
Antagonist Rhomboid major, rhomboid minor, trapezius
Identifiers
Latin musculus serratus anterior,
serratus lateralis
TA98 A04.4.01.008
TA2 2307
FMA 13397
Anatomical terms of muscle

The serratus anterior is a muscle of the chest. It originates at the side of the chest from the upper 8 or 9 ribs; it inserts along the entire length of the anterior aspect of the medial border of the scapula. It is innervated by the long thoracic nerve from the brachial plexus. The serratus anterior acts to pull the scapula forward around the thorax.

Contents

The muscle is named from Latin: serrare = to saw (referring to the shape); and anterior = on the front side of the body.

Structure

Origin

Serratus anterior normally originates by nine or ten muscle slips – arising from either the 1st to 8th ribs, or the 1st to 9th ribs; because two slips usually arise from the 2nd rib, the number of slips is greater than the number of ribs from which they originate. [1]

Insertion

The muscle is inserted along the medial border of the scapula between the superior and inferior angle of the scapula.

The muscle is divided into three parts according to the points of insertion: [1]

Innervation

The serratus anterior is innervated by the long thoracic nerve, a branch of the brachial plexus. [2] The long thoracic nerve travels inferiorly on the surface of the serratus anterior muscle.

Relations

The serratus anterior lies deep to the subscapularis, from which it is separated by the subscapularis (supraserratus) bursa. [3] It is separated from the rib by the scapulothoracic (infraserratus) bursa. [4]

Function

All three parts described above pull the scapula forward around the thorax, which is essential for anteversion of the arm. As such, the muscle is an antagonist to the rhomboids. However, when the inferior and superior parts act together, they keep the scapula pressed against the thorax together with the rhomboids and therefore these parts also act as synergists to the rhomboids. The inferior part can pull the lower end of the scapula laterally and forward and thus rotates the scapula to make elevation of the arm possible. Additionally, all three parts can lift the ribs when the shoulder girdle is fixed, and thus assist in respiration. [1]

The serratus anterior is occasionally called the "big swing muscle" or "boxer's muscle" because it is largely responsible for the protraction of the scapula — that is, the pulling of the scapula forward and around the rib cage that occurs when someone throws a punch.

The serratus anterior acts in concert with the upper and lower fibers of the trapezius muscle to sustain upward rotation of the scapula, which allows for overhead lifting.

Clinical significance

The long thoracic nerve that supplies the serratus anterior muscle is vulnerable during certain types of surgery (for example, during lymph node clearance from the axilla for breast cancer). Damage to this nerve is the most common cause of winged scapula. [5]

Other animals

The muscles of the shoulder can be categorized into three topographic units: the scapulohumeral, axiohumeral, and axioscapular groups. Serratus anterior forms part of the latter group together with rhomboid major, rhomboid minor, levator scapulae, and trapezius. The trapezius evolved separately, but the other three muscles in this group evolved from the first eight or ten ribs and the transverse processes of the cervical vertebrae (homologous to the ribs). [6]

Functional demands have resulted in the evolution of individual muscles from the basal unit formed by the serratus anterior. In primitive life forms, the main function of the axioscapular group is to control the movements of the vertebral border of the scapula: fibers concerned with the dorsal movement of scapula evolved into the rhomboids, those with ventral motion into serratus anterior, and those with cranial movements into levator scapulae. The evolution of the serratus anterior itself has resulted in (1) grouping of its distal and proximal fibers, (2) size reduction of its intermediate fibers, and (3) the insertion of its dominant superior and inferior parts onto the superior and inferior angles of the scapula. [6]

In primates, the thoracic cage is wide and the scapula is rotated onto its posterior side to have the glenoid cavity face laterally. Additionally, the clavicle takes care of medial forces. In cursorial mammals (for example the horse and other quadrupeds), the scapula is hanging vertically on the side of the thorax and the clavicle is absent. Therefore, in climbing animals, the serratus anterior supports the scapula against the reaction forces of the free limb and exerts high bending forces on the ribs. To sustain these forces, the ribs have a pronounced curvature and are supported by the clavicle. In cursorial animals, the thorax is hanging between the scapulae at the serratus anterior and pectoralis muscles. [7]

Additional images

See also

Notes

  1. 1 2 3 Platzer 2004 , p. 144
  2. Le Nail, L. R.; Bacle, G.; Marteau, E.; Corcia, P.; Favard, L.; Laulan, J. (June 2014). "Isolated paralysis of the serratus anterior muscle: surgical release of the distal segment of the long thoracic nerve in 52 patients". Orthopaedics & Traumatology, Surgery & Research. 100 (4 Suppl): S243–248. doi: 10.1016/j.otsr.2014.03.004 . ISSN   1877-0568. PMID   24703793.
  3. Giuseppe Milano; Andrea Grasso (December 16, 2013). Shoulder Arthroscopy: Principles and Practice. Springer Science & Business Media. pp. 549–. ISBN   978-1-4471-5427-3.
  4. Giuseppe Milano; Andrea Grasso (December 16, 2013). Shoulder Arthroscopy: Principles and Practice. Springer Science & Business Media. pp. 551–. ISBN   978-1-4471-5427-3.
  5. Martin, RM; Fish, DE (March 2008). "Scapular winging: anatomical review, diagnosis, and treatments". Current Reviews in Musculoskeletal Medicine. 1 (1): 1–11. doi: 10.1007/s12178-007-9000-5 . PMC   2684151 . PMID   19468892.
  6. 1 2 Brand 2008 , pp. 540–41
  7. Preuschoft 2004 , pp. 369–72

Related Research Articles

<span class="mw-page-title-main">Trapezius</span> Muscle between the lower spine and the shoulder blade

The trapezius is a large paired trapezoid-shaped surface muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae of the spine and laterally to the spine of the scapula. It moves the scapula and supports the arm.

<span class="mw-page-title-main">Scapula</span> Bone that connects the humerus (upper arm bone) with the clavicle (collar bone)

The scapula, also known as the shoulder blade, is the bone that connects the humerus with the clavicle. Like their connected bones, the scapulae are paired, with each scapula on either side of the body being roughly a mirror image of the other. The name derives from the Classical Latin word for trowel or small shovel, which it was thought to resemble.

Articles related to anatomy include:

<span class="mw-page-title-main">Brachial plexus</span> Network of nerves

The brachial plexus is a network of nerves formed by the anterior rami of the lower four cervical nerves and first thoracic nerve. This plexus extends from the spinal cord, through the cervicoaxillary canal in the neck, over the first rib, and into the armpit, it supplies afferent and efferent nerve fibers to the chest, shoulder, arm, forearm, and hand.

<span class="mw-page-title-main">Upper limb</span> Consists of the arm, forearm, and hand

The upper limbs or upper extremities are the forelimbs of an upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the digits, including all the musculatures and ligaments involved with the shoulder, elbow, wrist and knuckle joints. In humans, each upper limb is divided into the arm, forearm and hand, and is primarily used for climbing, lifting and manipulating objects.

<span class="mw-page-title-main">Levator scapulae muscle</span> Slender skeletal muscle at the back and side of the neck

The levator scapulae is a slender skeletal muscle situated at the back and side of the neck. It originates from the transverse processes of the four uppermost cervical vertebrae; it inserts onto the upper portion of the medial border of the scapula. It is innervated by the cervical nerves C3-C4, and frequently also by the dorsal scapular nerve. As the Latin name suggests, its main function is to lift the scapula.

<span class="mw-page-title-main">Rhomboid major muscle</span> Skeletal muscle in the human back

The rhomboid major is a skeletal muscle of the back that connects the scapula with the vertebrae of the spinal column. It originates from the spinous processes of the thoracic vertebrae T2–T5 and supraspinous ligament; it inserts onto the lower portion of the medial border of the scapula. It acts together with the rhomboid minor to keep the scapula pressed against thoracic wall and to retract the scapula toward the vertebral column.

<span class="mw-page-title-main">Rhomboid minor muscle</span> Skeletal muscle of the upper back

In human anatomy, the rhomboid minor is a small skeletal muscle of the back that connects the scapula to the vertebrae of the spinal column. It arises from the nuchal ligament, and the 7th cervical and 1st thoracic vertebrae and intervening supraspinous ligaments; it inserts onto the medial border of the scapula. It is innervated by the dorsal scapular nerve.

<span class="mw-page-title-main">Pectoralis minor</span> Human chest muscle that protracts the shoulder

Pectoralis minor muscle is a thin, triangular muscle, situated at the upper part of the chest, beneath the pectoralis major in the human body. It arises from ribs III-V; it inserts onto the coracoid process of the scapula. It is innervated by the medial pectoral nerve. Its function is to stabilise the scapula by holding it fast in position against the chest wall.

<span class="mw-page-title-main">Axilla</span> Area of the human body beneath the joint between arm and torso

The axilla is the area on the human body directly under the shoulder joint. It includes the axillary space, an anatomical space within the shoulder girdle between the arm and the thoracic cage, bounded superiorly by the imaginary plane between the superior borders of the first rib, clavicle and scapula, medially by the serratus anterior muscle and thoracolumbar fascia, anteriorly by the pectoral muscles and posteriorly by the subscapularis, teres major and latissimus dorsi muscle.

<span class="mw-page-title-main">Shoulder joint</span> Synovial ball and socket joint in the shoulder

The shoulder joint is structurally classified as a synovial ball-and-socket joint and functionally as a diarthrosis and multiaxial joint. It involves an articulation between the glenoid fossa of the scapula and the head of the humerus. Due to the very loose joint capsule ,that gives a limited interface of the humerus and scapula, it is the most mobile joint of the human body.

<span class="mw-page-title-main">Subscapularis muscle</span> Large triangle muscle of the shoulder

The subscapularis is a large triangular muscle which fills the subscapular fossa and inserts into the lesser tubercle of the humerus and the front of the capsule of the shoulder-joint.

<span class="mw-page-title-main">Shoulder girdle</span> Set of bones which connects the arm to the axial skeleton on each side

The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans, it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists of the clavicle, scapula, and coracoid. Some mammalian species have only the scapula.

<span class="mw-page-title-main">Posterior triangle of the neck</span> Region of the neck

The posterior triangle is a region of the neck.

<span class="mw-page-title-main">Supraspinous fossa</span> Part of the shoulderblade

The supraspinous fossa of the posterior aspect of the scapula is smaller than the infraspinous fossa, concave, smooth, and broader at its vertebral than at its humeral end. Its medial two-thirds give origin to the Supraspinatus.

<span class="mw-page-title-main">Triangle of auscultation</span>

The triangle of auscultation is a relative thinning of the musculature of the back, situated along the medial border of the scapula which allows for improved listening to the lungs.

<span class="mw-page-title-main">Winged scapula</span> Skeletal muscle condition around the shoulder blade

A winged scapula is a skeletal medical condition in which the shoulder blade protrudes from a person's back in an abnormal position.

<span class="mw-page-title-main">Axillary space</span>

The axillary spaces are anatomic spaces. through which axillary contents leave the axilla. They consist of the quadrangular space, triangular space, and triangular interval. It is bounded by teres major, teres minor, medial border of the humerus, and long head of triceps brachii.

<span class="mw-page-title-main">Outline of human anatomy</span> Overview of and topical guide to human anatomy

The following outline is provided as an overview of and topical guide to human anatomy:

The Eden–Lange procedure is an orthopedic procedure to alleviate the symptoms of trapezius palsy when more conservative measures, such as spontaneous resolution and surgical nerve repair are not promising. The rhomboid major, rhomboid minor, and levator scapulae muscles are transferred laterally along the scapula to replace the functions of the lower, middle, and upper fibers of the trapezius, respectively. The transferred muscles hold the scapula in a more medial and upwardly rotated position, without winging.

References