The Pectoral Region Flashcards
How many muscles are there in the pectoral region?
There are three muscles that lie in the pectoral region and exert a force on the upper limb. They are the pectoralis major, pectoralis minor, and the serratus anterior.
Describe pectoralis major.
This a large, fan shaped muscle, and is the most superficial muscle in the pectoral region. It also makes up most of the anterior wall of the axilla
The muscle has two heads – a clavicular head (attaches to the clavicle), and a sternocostal head (attaches to the sternum and ribs). Fibres from both heads attach to the edge of the intertubecular groove of the humerus.
The two heads can work independently or synergistically. Together, they act to adduct and medially rotate the humerus at the shoulder. The clavicular head also performs flexion.
The pectoralis major is innervated by the medial and lateral pectoral nerves, which are derived from the brachial plexus.
Describe pectoralis minor.
The pectoralis minor muscle is much smaller than the pectoralis major, and lies posterior (underneath) to it. With the pectoralis major, it forms part of the anterior wall of the axilla.
The muscle has a triangular shape, originating from the anterior surfaces of ribs 3 – 5. The fibres then converge to attach to the corocoid process of the scapula. Attaching to the scapula forms a ‘bridge’, which vessels passing into the upper limb must travel underneath
Contraction of the pectoralis minor depresses the shoulder (an inferior motion), and it is innervated by the medial pectoral nerve.
Describe serratus anterior.
The serratus anterior is found more laterally in the chest and, forms the medial wall of the axilla.
The muscle consists of several strips, which originate from ribs 2-8. They attach to the costal (rib facing) surface of the medial border of the scapula.
The main action of the serratus anterior is to rotate the scapula, allowing the arm to be raised over 90 degrees. It also holds the scapula against the ribcage – this is particularly useful when upper limb reaches anteriorly (e.g punching).
It is innervated by the long thoracic nerve
What is a ‘winged scapula’?
If damage to the long thoracic nerve occurs, the serratus anterior muscle will become paralysed. When pushing with the affected limb, the scapula is no longer held against the rib cage, and protrudes out of the back. It is said to have a ‘winged’ appearance.
The long thoracic nerve can become damaged by trauma to the shoulder, repetitive movements involving the shoulder or by structures becoming inflamed and pressing on the nerve.
What is the blood supply of pectoralis major?
Pectoral branch of the thoracoacromial trunk.
What is the blood supply to pectoralis minor?
Pectoral branch of the thoracoacromial trunk.
What is the blood supply to serratus anterior?
Lateral thoracic artery.
Why should the deep fascia on the anterior surface of pectoralis major not be fused to the fascia of the mammary gland?
It is an important clinical sign of breast cancer.
How does the medial nerve gain access to pectoralis major to innervate it?
Branches of medial pectoral nerve usually pierce pectoralis minor to reach the pectoralis major muscle
Name the venous drainage of pectoralis major.
Thoracoacromial vein (draining into axillary vein)
Name the venous drainage of pectoralis minor.
Thoracoacromial vein (draining into axillary vein)
Name the venous drainage of serratus anterior.
Lateral thoracic vein
