Serratus Anterior
By : Fahad Al-BakNaming: -
/ser-A-tus an-TEE-ri-or/
From the name we learn that the muscle is serrated in shape and is anterior.
From the name we learn that the muscle is serrated in shape and is anterior.
General: -
It is a lined muscle lays in-between the ribs and the scapula.
It makes the lateral wall of the thorax wall and the medial aspect of the axilla.
This broad sheet of thick muscle was named because of the saw-toothed appearance of its fleshy slips or digitations.
Loose fascia exists between the deep surface of the muscle and the ribs or intercostal fascia, and also between its superficial surface and subscapularis in order to facilitate free movement of the scapula.
It makes the lateral wall of the thorax wall and the medial aspect of the axilla.
This broad sheet of thick muscle was named because of the saw-toothed appearance of its fleshy slips or digitations.
Loose fascia exists between the deep surface of the muscle and the ribs or intercostal fascia, and also between its superficial surface and subscapularis in order to facilitate free movement of the scapula.
Supply: -
-Blood supply comes from The Dorsal Scapular Artery (a branch of the Subclavian Artery) and the Lateral Thoracic Artery (a branch of the Axillary Artery) and the Superior Thoracic Artery (a branch of the Axillary Artery).
-Nerve supply comes from The Long Thoracic Nerve C5, C6, C7.
Origin & Insertion: -
-Origin: just anterior to the midaxillary line to the outer surfaces of the upper eight or nine ribs and the intervening intercostal fascia. The upper digitation arises from ribs one and two, whereas each of the remaining digitations arises from a single rib. The lower four digitations interdigitate with the costal attachment of external oblique of the abdomen.
-Insertion: attachment the muscle fibers run backwards to insert into the costal surface of the medial border of the scapula between the superior and inferior angles. The digitations are not, however, evenly distributed in their attachment to the scapula. The first passes almost horizontally to the superior angle, while the lower four condense to attach to the inferior angle, with the intervening ones spread along the medial border.
Motion & Action: -
( Protracts the scapula at the scapulocostal joint, Upwardly rotates the scapula at the scapulocostal joint )
Serratus anterior is a major protractor of the pectoral girdle and as such is involved in all thrusting, pushing and punching movements where the scapula is driven forwards carrying the upper limb with it.
Note the massive development of this muscle in boxers.
It plays a vital role in stabilizing the scapula during movements of the upper limb and contracts strongly to hold the medial border of the scapula against the chest wall when the arm is flexed or when a weight is carried in front of the body. Failure to perform this action, as when paralyzed, results in ‘winging’ of the scapula in which the medial border stands away from the chest wall, thus severely affecting the function and mobility of the upper limb.
The lower digitations of the muscle work together with trapezius to rotate the scapula laterally, so that the glenoid fossa looks upwards and forwards.
When paralyzed, loss of the rotating action of serratus anterior means that the upper limb cannot be abducted by more than approximately 90 degrees, thereby seriously limiting the functional capacity of the upper limb.
There is some controversy as to whether serratus anterior acts as an accessory muscle of inspiration during respiratory distress.
The line of action of the muscle fibers, except perhaps for the first two digitations and maybe the last, are not directed to cause elevation of the ribs. Indeed, they are more likely to cause depression of the ribs.
Serratus anterior is a major protractor of the pectoral girdle and as such is involved in all thrusting, pushing and punching movements where the scapula is driven forwards carrying the upper limb with it.
Note the massive development of this muscle in boxers.
It plays a vital role in stabilizing the scapula during movements of the upper limb and contracts strongly to hold the medial border of the scapula against the chest wall when the arm is flexed or when a weight is carried in front of the body. Failure to perform this action, as when paralyzed, results in ‘winging’ of the scapula in which the medial border stands away from the chest wall, thus severely affecting the function and mobility of the upper limb.
The lower digitations of the muscle work together with trapezius to rotate the scapula laterally, so that the glenoid fossa looks upwards and forwards.
When paralyzed, loss of the rotating action of serratus anterior means that the upper limb cannot be abducted by more than approximately 90 degrees, thereby seriously limiting the functional capacity of the upper limb.
There is some controversy as to whether serratus anterior acts as an accessory muscle of inspiration during respiratory distress.
The line of action of the muscle fibers, except perhaps for the first two digitations and maybe the last, are not directed to cause elevation of the ribs. Indeed, they are more likely to cause depression of the ribs.
In The Field Notes: -
Test the serratus anterior: the hand of the outstretched limb is pushed against a wall. If the muscle is acting normally, several digitations of the muscle can be seen and palpated.
Clinical Note: -
Paralysis: Isolated serratus anterior paralysis is a rare condition that is secondary to direct trauma or overuse. Patients complain of neuropathic pain and/or muscle pain secondary to overexertion of the other shoulder stabilizing muscles.
Relations: -
From the posterior perspective, the majority of the serratus anterior lies deep to the scapula and the latissimus dorsi.
From the anterior perspective, much of the muscle lies deep to the pectoralis major and minor.
The serratus anterior is superficial anterolaterally on the trunk where it meets the external abdominal oblique.
The lowest four to five slips of the costal (i.e., rib) attachments of the serratus anterior interdigitate with the external abdominal oblique.
The serratus anterior lies next to (anterior to) the subscapularis.
The serratus anterior is located within the spiral line myofascial meridian.
From the anterior perspective, much of the muscle lies deep to the pectoralis major and minor.
The serratus anterior is superficial anterolaterally on the trunk where it meets the external abdominal oblique.
The lowest four to five slips of the costal (i.e., rib) attachments of the serratus anterior interdigitate with the external abdominal oblique.
The serratus anterior lies next to (anterior to) the subscapularis.
The serratus anterior is located within the spiral line myofascial meridian.
Sources: -
- Moore - Clinically Oriented Anatomy 7th Edition (699-700).
- Joseph E Muscolino - The Muscular System Manual: The Skeletal Muscles of the Human Body
Book 4t edition (104-106).
-Nigel Palastanga & Roger Soames Anatomy and Human Movement Structure and Function 6th edition (54-55).
- Joseph E Muscolino - The Muscular System Manual: The Skeletal Muscles of the Human Body
Book 4t edition (104-106).
-Nigel Palastanga & Roger Soames Anatomy and Human Movement Structure and Function 6th edition (54-55).
