Flashcards in TBL5 - Pectoral Muscles & Breasts Deck (22):
Where are the pectoralis major and minor located?
1) The pectoralis major is a large, fan-shaped muscle that covers the superior part of the thorax
2) The pectoralis minor lies in the anterior wall of the axilla where it is almost completely covered by the much larger pectoralis major
What are the proximal and distal attachments of the pectoralis major?
1) Proximal attachment:
a) Clavicular head: anterior surface of medial half of clavicle
b) Sternocostal head: anterior surface of sternum, superior six costal cartilages, aponeurosis of external oblique muscle
2) Distal attachment: Lateral lip of intertubercular sulcus of humerus
What is the function of the pectoralis major?
1) Adducts and medially rotates humerus; draws scapula anteriorly and inferiorly
2) Acting alone, clavicular head flexes humerus and sternocostal head extends it from the flexed position
What innervates the pectoralis major?
1) Sternocostal head (C7, C8, T1) - Lateral & Medial cutaneous nerve
2) Clavicular head (C5, C6) - Lateral cutaneous nerve
What innervates the pectoralis minor?
Medial pectoral nerve (C8, T1)
What are the proximal and distal attachments of the pectoralis minor?
1) Proximal: 3rd–5th ribs near their costal
2) Distal: Medial border and superior surface of coracoid process of scapula
What is the function of the pectoralis minor?
Stabilizes scapula by drawing it inferiorly and anteriorly against thoracic wall
What are the proximal and distal attachments of the serratus anterior?
1) Proximal: External surfaces of lateral parts
of 1st–8th ribs
2) Distal: Anterior surface of medial border of scapula
What is the function of the serratus anterior?
1) Protracts scapula and holds it against thoracic wall
2) Rotates scapula
What innervates the serratus anterior?
Long thoracic nerve (C5, C6, C7)
What allows for upward rotation of the scapula?
The serratus anterior works synergistically with the superior and inferior parts of the trapezius to rotate the scapula upward thereby enabling the deltoid to fully abduct the arm above the horizontal plane
Why is the long thoracic nerve vulnerable to injury and how are abduction and rotation at the glenohumeral joint hindered after its injury? How does the winged scapula deformation occur?
1) When the serratus anterior is paralyzed owing to injury to the long thoracic nerve, the medial border of the scapula moves laterally and posteriorly away from the thoracic wall, giving the scapula the appearance of a wing, especially when the person leans on a hand or presses the upper limb against a wall
2) When the arm is raised, the medial border and inferior angle of the scapula pull markedly away from the posterior thoracic wall, a deformation known as a winged scapula
3) In addition, the upper limb may not be able to be abducted above the horizontal position because the serratus anterior is unable to rotate the glenoid cavity superiorly to allow complete abduction of the limb
4) Remember, the trapezius also helps raise the arm above the horizontal. Although protected when the limbs are at one’s sides, the long thoracic nerve is exceptional in that it courses on the superficial aspect of the serratus anterior, which it supplies. Thus when the limbs are elevated, as in a knife fight, the nerve is especially vulnerable. Weapons, including bullets directed toward the thorax, are a common source of injury
What are the pectoral muscles derived from?
The pectoral muscles are derivatives of myoblasts in the parietal layer of lateral plate mesoderm
What is the Poland sequence?
1) A Poland sequence is characterized by absence of the pectoralis minor and partial loss of the pectoralis major (usually the sternal head) muscles
2) The nipple and areola are absent or displaced, and there are often digital defects (syndactyly [fused digits] and brachydactyly [short digits]) on the affected side
3) Can be problematic in females due to breast development
How do mammary glands and nipples form?
1) Paired mammary glands are modified apocrine sweat glands with a cutaneous origin. Present in both males and females, they consist of parenchyma, which is formed from ducts, and connective tissue stroma. Parenchyma derives embryonically from surface ectoderm; stroma arises from surrounding mesenchyme
2) The 6-week embryo has two ventral ridge-like thickenings of epidermis, the mammary (milk) lines, extending from axillae to the inguinal area. The major part of each ridge disappears almost immediately, but one pair remains in the pectoral area and penetrates the mesenchyme
3) Then, 15-25 solid epithelial cords develop from each and are later canalized to form future lactiferous ducts. Mesenchyme gives rise to loose connective tissue around each duct. Denser connective tissue forms septa between them to divide the gland into lobes
What occurs to the breasts through childhood and puberty?
1) In childhood, the breasts consist of 15-25 rudimentary lactiferous ducts that open onto the surface of the nipple
2) During puberty, ovarian estrogen and progesterone induce budding of multiple, small terminal ducts from the distal end of each lactiferous duct. The ovarian hormones also induce white fat accumulation between the budding terminal ducts
What occurs to the breasts during pregnancy?
1) During pregnancy, the ovarian hormones and prolactin from the pituitary gland stimulate secretory acini formation from distal ends of the terminal ducts
2) The hormones also induce milk secretion into the lumens of the acini during lactation
What occurs to the breasts after breast feeding? What occurs to the breasts after menopause?
1) After breast-feeding, the breasts return to their resting state
2) After menopause, acini and terminal ducts regress but remaining lactiferous ducts can transform into fluid-filled cysts
On what muscles do they breasts lie on?
Two-thirds of each breast lies on the pectoralis major muscle and one-third rests on the serratus anterior muscle
What firmly attaches to the breasts to the overlying dermis of the skin?
1) The mammary glands are firmly attached to the dermis of the overlying skin, especially by substantial skin ligaments
(L. retinacula cutis), the suspensory ligaments
2) These condensations of fibrous connective tissue, particularly well developed in the superior part of the gland, help support the lobes and lobules of the mammary gland
Where does lymph from the lateral and medial quadrants of the breasts drain to?
1) Most lymph formed in lateral quadrants of the breasts drains initially into the pectoral lymph nodes, a constituent group of the axillary nodes
2) Lymph from the medial quadrants drains into the parasternal lymph nodes that, like the axillary nodes, drain mainly into the supraclavicular lymph nodes