Muscles of the Pectoral Region Flashcards
How many muscles lie in the pectoral region?
4
What do the muscles in the pectoral region do?
Exert a force on the upper limb
What are the muscles of the pectoral region?
Pectoralis major
Pectoralis minor
Serratus anterior
Subclavius
What is the most superficial of the muscles in the pectoral region?
Pectoralis major
What shape is the pectoralis major?
Large, fan shaped
What does the pectoralis major make up?
Most of the anterior wall of the axilla
What does the pectoralis major have?
Two heads- a clavicular head, and a sternocostal head
Where is the insertion of the pectoralis major?
The lateral lip of the intertubercular sulcus of humerus
How can the two heads of the pectoralis major work?
Independently or synergistically
What do the two heads of the pectoralis major produce when working together?
Adducts and medially rotates the humerus at the shoulder, and draws the scapula anteriorly and inferiorly
What does the clavicular head of the pectoralis major do when acting alone?
Flexes humerus
What does the sternocostal head of the pectoralis major do when acting alone?
Extends the humerus from the flexed position
What innervates the pectoralis major?
Lateral and medial pectoral nerve, derived from the brachial plexus
The clavicular head by C5 and C6
The sternocostal head C7, C8 and T1
What is the arterial supply of the pectoralis major?
Pectoral and deltoid branches of the thoracoacromial artery, anterior intercostal arteries and perforating branches of internal thoracic artery
How does the pectoralis minor muscle differ from the pectoralis major?
It is much smaller, and more posterior
What does the pectoralis form?
With the pectoralis major, forms part of the anterior wall of the axilla
What shape is the pectoralis minor?
Triangular
What does the attachment of the pectoralis minor to the scapula form?
A ‘bridge’, which vessels passing into the upper limb must travel underneath
What is the function of the pectoralis minor?
Stabilises the scapula by drawing it inferiorly and anteriorly against the thoracic wall (depressing the shoulder)
What is the pectoralis minor innervated by?
Medial pectoral nerve (C8, T1)
What is the arterial supply of the pectoralis minor?
Pectoral and deltoid branches of thoracoacromial artery
Where is the serratus anterior muscle found?
More laterally in the chest
What does the serratus anterior muscle form?
The medial wall of the axilla
What does the serratus anterior consist of?
Several strips
What is the innervation of the serratus anterior?
Long thoracic nerve
What is the main function of the serratus anterior?
Rotate the scapula, allowing the arm to be held above 90º
Protracts the scapula and hold it against the thoracic wall
What is the arterial supply of the serratus anterior?
Lateral thoracic artery
What happens if damage to the long thoracic nerve occurs?
The serratus anterior muscle will become paralysed
What is the result of paralysation of the serratus anterior?
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
When can the long thoracic nerve 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 innervation of the subclavius?
Nerve to subclavius
What is the main action of the subclavius?
Anchors and depresses clavicle
What is the arterial supply to the subclavius?
Clavicular branch of the thoracoacromial artery
