MUSCLES OF PECTORAL REGION

INTRODUCTION:
  • The pectoral region is located on the anterior chest wall.
  • It contains four muscles that exert a force on the upper limb the pectoralis major, pectoralis minor, serratus anterior and subclavius.
PECTORALIS MAJOR:
  • The pectoralis major is the most superficial muscle in the pectoral region.
  • It is large and fan shaped, and is composed of a sternal head and a clavicular head.
  • Forms anterior axillary fold
  1. It is preserved in postero lateral thoractomy
  2. Attachments: The distal attachment of both heads is into the intertubercular sulcus of the humerus.
  • Clavicular head – originates from the anterior surface of the medial clavicle.
  • Sternocostal head – originates from the anterior surface of the sternum, the superior six costal cartilages and the aponeurosis of the external oblique muscle.
  1. Function: Adducts and medially rotates the upper limb, and draws the scapular anteroinferiorly. The clavicular head also acts individually to flex the upper limb.
  2. Innervation: Lateral and medial pectoral nerves.
  3. Blood supply of pectoralis major:
  • Pectoralis major derives its blood supply mainly from pectoral branch of the thoracoacromial artery.
  • Other arteries supplying the muscle are: First perforating branch of the internal thoracic artery (Internal mammary artery) and intercostal artery.
PECTORALIS MINOR:
  • The pectoralis minor lies underneath its larger counterpart muscle, pectoralis major.
  • Both of these muscles form part of the anterior wall of the axilla region.
  • Pectoralis minor crosses in front of axillary artery and divides it into three parts. 
  • The anterior relation of each part are; First part lies behind the pectoralis major muscle, second part lies behind the pectoralis minor and major muscle and third part lies behind pectoralis major.
  • Removal of pectoralis minor and preservation of pectoralis major in Patey's mastectomy
  • It is the only shoulder girdle muscle which is not inserted on the bone in free upper limb.
  • Attachments: Originates from the 3rd-5th ribs, and inserts into the coracoid process of the scapula.
  • Function: Stabilizes the scapula by drawing it anterioinferiorly against the thoracic wall.
  • Innervation: Medial pectoral nerve.
SERRATUS ANTERIOR:
  • The serratus anterior is located more laterally in the chest wall, and forms the medial border of the axilla region.
  • Cut in posterio lateral thoractomy
  • It is responsible for keeping the scapula applied to the thoracic wall, and protracts and rotates the scapula.
  • Attachments: The muscle consists of several strips, which originate from the lateral aspects of ribs 1-8. They attach to the costal (rib facing) surface of the medial border of the scapula.
  • Function: Rotates the scapula, allowing the arm to be raised over 90 degrees. It also holds the scapula against the rib cage(forward).Helps in forced inspiration
  • Innervation: Long thoracic nerve(C5,6,7)
SUBCLAVIUS:
  • The subclavius is small muscle, which is located directly underneath the clavicle, running horizontally. It affords some minor protection to the underlying neurovascular structures (e.g in cases of clavicular fracture or other trauma).
  • Attachments: Originates from the junction of the 1st rib and its costal cartilage, inserting into the inferior surface of the middle third of the clavicle.
  • Function: Anchors and depresses the clavicle.
  • Innervation: Nerve to subclavius.
CLINICAL SIGNIFICANCE:
  • Winging of the Scapula
  • One of the actions of the serratus anterior is to ‘hold’ the scapula against the ribcage.
  • If the long thoracic nerve is damaged (and the serratus anterior therefore paralysed), a specific clinical sign is produced.
  • In cases such as this, the scapula is no longer held against the ribcage – and protrudes out of the back. It is said to have a ‘winged’ appearance.
  • Long thoracic nerve palsy is thought to most commonly occur from traction injuries, where the upper limb is stretched violently.
Breast implant
  • It is mostly placed beneath the pectoralis major muscle, it is never dissected. 
  • A complete musculofascial pocket is created by lateral and inferiolateral dissection of the pectoralis minor and serratus anterior.
Congenitally missing muscles
  • Pectoralis major and minor muscles are the most common congenitally absent muscles in humans.
Exam Question
  • pectoralis major Forms anterior axillary fold

  • pectoralis major is not cut in posterio lateral thoractomy
  • pectoralis major insert into the intertubercular sulcus of the humerus
  • pectoralis major blood supply is mainly from pectoral branch of the thoracoacromial artery
  • Pectoralis minor crosses in front of axillary artery and divides it into three parts.
  • Removal of pectoralis minor and preservation of pectoralis major in Patey's mastectomy
  • Pectoralis minor is the only shoulder girdle muscle which is not inserted on the bone in free upper limb.
  • Pectoralis minor inserts into the coracoid process of the scapula.
  • Pectoralis minor draw scapula anterioinferiorly

  • serratus anterior is Cut in postero lateral thoractomy 
  • serratus anterior protracts and rotates the scapula
  • serratus anterior attach to the costal (rib facing) surface of the medial border of the scapula
  • serratus anterior holds the scapula against the rib cage(forward).Helps in forced inspiration
  • serratus anterior is innervated by Long thoracic nerve(C5,6,7)
  • serratus anterior lesion results in Winging of the Scapula
  • pectoralis major muscle, it is never dissected in breast implant surgery
  • Pectoralis major and minor muscles are the most common congenitally absent muscles in humans.

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