The Pectoral region
The skin of the pectoral region is supplied by cutaneous nerves, as follows:
1) The supraclavicular nerves, which are divided into three groups: medial, intermediate and lateral.
2) The anterior cutaneous nerves, which are the terminal branches of the anterior intercostal nerves.
3) The lateral cutaneous nerves, which are the lateral branches of the intercostal nerves.
1) The supraclavicular nerves, which are divided into three groups: medial, intermediate and lateral.
2) The anterior cutaneous nerves, which are the terminal branches of the anterior intercostal nerves.
3) The lateral cutaneous nerves, which are the lateral branches of the intercostal nerves.
The Breast
The breast is hemispherical in shape and lies in the superficial fascia of the pectoral region. It extends from the 2nd rib to the 6th rib and from the lateral margin of the sternum to the mid-axillary line. The breast has a small axillary tail which pierces the deep fascia of the axilla.
The Structure of the Breast
The breast is covered with skin which contains a pink or light brown circular area surrounding the base of the nipple called the areola. It contains modified sebaceous glands which enlarge to form tubercles, called tubercles of Montgomery, in pregnant and lactating women. The nipple is a conical projection from the breast, level with the 4th intercostal space. Around 15-20 lactiferous ducts open by small orifices at the tip of the nipple. The ligaments of Cooper extend from the skin to the pectoral fascia to form the fibrousstroma, while the fattystroma forms the main bulk of the gland.The parenchyma is formed by the glandular tissue which consists of 15-20 lobes. Each lobe consists of a cluster of alveoli and is drained by a lactiferous duct which dilates to form a lactiferous sinus beneath the areola.
Blood supply of the breast
The arterial supply to the breast is as follows:
1) Internal thoracic artery.
2) Lateral thoracic artery.
3) Intercostal arteries.
The venous drainage is via:
1) The internal thoracic vein.
2) The axillary vein.
3) The intercostal vein.
1) Internal thoracic artery.
2) Lateral thoracic artery.
3) Intercostal arteries.
The venous drainage is via:
1) The internal thoracic vein.
2) The axillary vein.
3) The intercostal vein.
Nerve supply
The anterior and lateral cutaneous branches of the 4th to 6th intercostal nerves provide the nerve supply to the breast.
Lymphatic drainage of the breast
About 75% of the lymph from the breast drains into the axillary lymph nodes, 20% into the internal thoracic nodes and 5% into the posterior intercostal nodes.
The breast is divided into four quadrants, the lateral part of the breast drains into the anterior, posterior, lateral, central and apical groups of axillary lymph nodes. The medial part of the breast drains to lymph nodes around the internal thoracic artery (parasternal), cross the midline to the opposite side, the posterior intercostal lymph nodes and the subdiphragmatic.
The breast is divided into four quadrants, the lateral part of the breast drains into the anterior, posterior, lateral, central and apical groups of axillary lymph nodes. The medial part of the breast drains to lymph nodes around the internal thoracic artery (parasternal), cross the midline to the opposite side, the posterior intercostal lymph nodes and the subdiphragmatic.
Figure1: Pectoral Region & clavipectoral triangle.
Muscles connecting the upper limbs to the thoracic wall
Pectoralis major
Origin
The clavicular head originates from the medial 1/2 of the anterior surface of the clavicle, anterior surface of the sternum, upper seven costal cartilages and aponeurosis of external oblique muscle.
Insertion
To the lateral lip of the bicipital groove of the humerus.
Nerve supply
The medial and lateral pectoral nerves.
Actions
1) Adduction, flexion and medial rotation of the arm.
2)The clavicular head flexes the extended arm.
3)The sternocostal head extends the flexed arm.
The clavicular head originates from the medial 1/2 of the anterior surface of the clavicle, anterior surface of the sternum, upper seven costal cartilages and aponeurosis of external oblique muscle.
Insertion
To the lateral lip of the bicipital groove of the humerus.
Nerve supply
The medial and lateral pectoral nerves.
Actions
1) Adduction, flexion and medial rotation of the arm.
2)The clavicular head flexes the extended arm.
3)The sternocostal head extends the flexed arm.
Figure2: Pectoralis major
Pectoralis minor
Origin
From the anterior surface of the 3rd, 4th and 5th ribs and the deep fascia of the adjacent intercostal spaces.
Insertion
To the upper surface and the medial border of the coracoid process.
Nerve supply
The medial pectoral nerve.
Action
1) Protracts the scapula forwards
2) Depresses the shoulder.
From the anterior surface of the 3rd, 4th and 5th ribs and the deep fascia of the adjacent intercostal spaces.
Insertion
To the upper surface and the medial border of the coracoid process.
Nerve supply
The medial pectoral nerve.
Action
1) Protracts the scapula forwards
2) Depresses the shoulder.
Figure3: Pectoralis minor & subclavius
Figure4: Pectoralis major and minor and subclavius
Subclavius
Origin
From the the costochondral junction of the upper surface of the first rib.
Insertion
Subclavian groove on the inferior surface of the middle third of the clavicle.
Nerve supply
Nerve to subclavius from the upper trunk of the brachial plexus.
Action
Steadies the clavicle during movements of the shoulder
Serratus anterior
Origin
From the outer surfaces of the upper eight ribs.
Insertion
To the ventral surface of the superior angle, medial border and inferior angle of the scapula.
Nerve supply
Long thoracic nerve.
Actions
1) Pulls the scapula forwards (protraction).
2) Fixation of the scapula on the chest wall.
3) Pulls the inferior angle of the scapula forward around the chest wall.
From the the costochondral junction of the upper surface of the first rib.
Insertion
Subclavian groove on the inferior surface of the middle third of the clavicle.
Nerve supply
Nerve to subclavius from the upper trunk of the brachial plexus.
Action
Steadies the clavicle during movements of the shoulder
Serratus anterior
Origin
From the outer surfaces of the upper eight ribs.
Insertion
To the ventral surface of the superior angle, medial border and inferior angle of the scapula.
Nerve supply
Long thoracic nerve.
Actions
1) Pulls the scapula forwards (protraction).
2) Fixation of the scapula on the chest wall.
3) Pulls the inferior angle of the scapula forward around the chest wall.
