Monday, February 25, 2008

PECTORAL REGION

PECTORAL REGION
It is composed of muscles of the pectoral region which include: The Pectoralis major, Pectoralis minor and subclavius muscle.
The pectoralis major muscle is enclosed by a fascia known as pectoral fascia while the pectoralis minor and subclavius muscles are enclosed by a deep fascia known as clavipectoral fascia. The bone of the pectoral region is the clavicle. On the anterior aspect of the pectoral region is the breast.

PECTORALIS MAJOR MUSCLE
It is a thick triangular muscle, it is also fan shaped which arises by means of 2 heads that are continuous with each other, it is the most superficial muscle of the pectoral region.
ORIGIN
1. The clavicular head arises from the medial 2/3rd of the clavicle.
2. The sternocoastal head arises from the anterior half of the sternum, coastal cartilage of the upper six ribs and the aponeurosis of the external oblique abdominus muscle.

INSERTION
It is inserted into the lateral lip of the bicipital grove or intertubercular sulcus of the humerus by means of a thick bilaminar tendon which is about 5cm in length.
NERVE SUPPLY
Its nerve supply is derived from 2 sources.
1. lateral pectoral nerves a branch from the lateral cord of the brachial plexus
2. medial pectoral nerve a branch from the medial cord of the brachial plexus.
The Lateral pectoral nerve pierces the clavipectoral fascia to supply the clavicular head while the medial pectoral nerve pierces the pectoralis minor to supply sternocoastal head of the pectoralis major.

ACTION
1. Adduction {humeral}
2. medial rotation
3. Flexion at the shoulder joint
4. Extension at the shoulder joint
Flexion at the shoulder joint and ability to use the thumb to touch the tip of the shoulder is a function of the clavicular head while the Sternocoastal head extends the shoulder joint against resistance. The two heads of the pectoralis major acting together with other muscles of the scapular region causes humeral adduction and medial rotation of the humerus

PECTORALIS MINOR
It is a small muscle that lie posterior to the pectoralis major. The outline of the pectoralis minor is a very important landmark in the upper limb. The p. minor is synonymous to the piriformis muscle of the gluteal region.
ORIGIN
The pectoralis minor arises from the 3rd to 5th rib sometimes it can also arise from the 2nd rib or extend up to the 6th rib close to their costochondral junction.
INSERTION
It is inserted into the medial part of the superior Surface of the coracoid process but it is not uncommon to find the tendon passing the coracoid process to blend with the coracoclavicular ligament or even to the coracohumeral ligament.
Sometimes muscle fibers arising from the 1st rib to the coracoid process are referred to as pectoralis minimus.
NERVE SUPPLY
It is supplied by the
1. Medial pectoral nerve
2. Lateral pectoral nerve though this is not by a direct branch but a communicating branch sent as a loop to the medial pectoral nerve.
ACTION
1. Forward and downward pull of the scapular.
2. Serve as an accessory muscle of respiration.
3. Causes depression of the shoulder.

SUBCLAVIUS
It is a small triangular muscle lying between the clavicle and the 1st rib. It arises from the 1st rib, close to the costochondral junction it ascends laterally to be inserted into the medial 2/3rd of the inferior surface of the clavicle at the area known as the subclavian groove.

NERVE SUPPLY
Nerve to subclavius which is derived from the brachial plexus just before the upper trunk is formed
ACTION
The subclavius muscle stabilizes the clavicle at the stenoclavicular joint though the strength of the stenoclavicular ligament supersedes this role. Actually because it is difficult to palpate its action is more imagined than real.
In cases of fracture of the clavicle it serves as a cushion to prevent the jagged edge from lacerating the vessels (subclavian vessels) that pass below it.

CLAVIPECTORAL FASCIA
It is a thickened fascia that lies below the clavicular head of the pectoralis major. It fills in the space between the clavicle and the p. minor. It is attached laterally to the coracoid process and medially it fuses with the external intercostals membrane of the upper two intercostal spaces. It is also attached medially to the 1st rib, between the 1st rib and the coracoid process the fascia is thinckened to form the costocoracoid ligament. Superiorly the clavipectoral fascia split to enclose the subclavius muscle it then get attached to the anterior and posterior surface of the clavicle in relation to the subclavian groove. Inferiorly on getting to the superior border of the pectoralis minor it splits to enclose the pectoralis minor then on the lower border of pectoralis minor it fuses again descending to get attached to the axillary fascia forming the suspensory ligament of the axillary fascia. The clavipectoral fascia is pieced by the following structures:
1. The lateral pectoral nerve
2. The thoracoacomial artery
3. The cephalic vein
4. The lymphatic vessels.

THE PECTORALIS FASCIA
It is a deep fascia enclosing the pectoralis major muscle. Superiorly it is attached to the clavicle while posteroinferiorly it extends to the scapular region forming the axillary fascia. In the axilla it is pierced by the axillary tail of Spence of breast at the level of the 3rd intercostal space, the opening created there is referred as foramen of Langer

7 comments:

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snoozy said...
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