Origin
It arises by a series of eight digitations from upper eight
ribs. The first digitation arises from the first and second
ribs, whereas all other digitations arise from their cor-
responding ribs.
tha above statement is based on serratus anterior.
Can any one please explain how the first and second rib has same origin and yet has 8 digitalis coming from first 8 ribs??
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Answers
Answer:
It originates from several sites on the outer aspects of the first eight - occasionally nine - ribs between their respective angles and costal cartilages. The first 'digitation' or muscular slip is anomalous in that it arises from both the first and second ribs.
Explanation:
Serratus anterior normally originates by nine or ten slips (muscle branches) from either the first to ninth ribs or the first to eighth ribs. Because two slips usually arise from the second rib, the number of slips is greater than the number of ribs from which they originate.[1]
The muscle is inserted along the medial border of the scapula between the superior and inferior angles along with being inserted along the thoracic vertebrae. The muscle is divided into three named parts depending on their points of insertions:[1]
the serratus anterior superior is inserted near the superior angle
the serratus anterior intermediate is inserted along the medial border
the serratus anterior inferior is inserted near the inferior angle.
Relations
The serratus anterior lies deep to the subscapularis, from which it is separated by the subscapularis (supraserratus) bursa.[2] It is separated from the rib by the scapulothoracic (infraserratus) bursa.[3]
Innervation
The serratus anterior is innervated by the long thoracic nerve, a branch of the brachial plexus.[4] The long thoracic nerve travels inferiorly on the surface of the serratus anterior muscle.
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 also plays an important role in the upward rotation of the scapula, such as when lifting a weight overhead. It performs this in sync with the upper and lower fibers of the trapezius.[5