Session 6: Pectoral Region and Axilla Flashcards
What muscles can be found in the pectoral region?
Pectoralis Major Pectoralis Minor Serratus Anterior Coracobrachialis Subclavius Deltoid
Location and structure of pectoralis major
Most superficial muscle in the pectoral region.
Triangular shape
Sternocostal head and a clavicular
Origination of the pectorals major and insertion. (Several originations)
Clavicular head originates from anterior surface of medial clavicle.
Sternocostal head originates from the anterior surface of the sternum, upper six costal cartilages and aponeurosis of external oblique muscle.
Inserts into intertubercular sulcus of the humerus.
Actions of the pectoralis major
If arm is abducted at shoulder join, contraction of sternocostal head pulls the humeral insertion towards the fixed sternocostal origin, and therefore adducts the arm.
If upper limb starts in the anatomical position contraction of clavicular head will flex the arm at the shoulder joint
If the humerus is already laterally rotated at the shoulder joint, contraction of pectoralis major will medially rotate it.
Innervation of pectoralis major
Medial pectoral nerve (C8-T1)
Lateral pectoral nerve (C5-C7)
Location and structure of pectoralis minor.
Origination and insertion.
Lies deep to pectoralis major
Originates from 3rd to 5th rib
Inserts into coracoid process of the scapula
Action of pectoralis minor
Stabilises the scapula by drawing it anteroinferiorly against the thoracic wall.
Innervation of pectoralis minor
Medial pectoral nerve (C8-T1)
Location of serratus anterior
More laterally on the chest wall
Origination and insertion of serratus anterior.
Originates as separate parts from the lateral aspect of ribs 1-8, or 1-9.
Inserts into the costal surface (rib-facing) of its medial border.
Action of serratus anterior.
Protracts (pulls back) the scapula
Rotates the medial border of the scapula anteroinferiorly causing the glenoid cavity to rotate upwards.
Why is the rotation of the medial border of the scapula important?
It enables the upper limb to be abducted above 90 degrees at the shoulder
Innervation of serratus anterior.
Long thoracic nerve (C5-C7)
Location of coracobrachialis.
Lies deep to the biceps brachii in arm.
Origination and insertion of coracobrachialis.
Originates from the coracoid process of the scapula.
Inserts onto the medial side of the humeral shaft.
Action of coracobrachialis.
Innervation of coracobrachialis.
Action: flexes arm at the shoulder and a weak adductor
Innervation: Musculocutaneous nerve (C5-C7)
Location of subclavius.
Located directly underneath the clavicle and runs parallel (horizontal).
Origination and insertion of subclavius.
Originates from the junction of the first rib and its costal cartilage and inserts onto the inferior surface of the middle third of the clavicle.
Action and innervation of subclavius.
Anchors and depresses the clavicle.
Innervation from nerve to subclavius.
Location of deltoid and features.
Triangular muscle. Divided into anterior, middle and posterior part.
Origination and insertion of deltoid.
Originates from the anterior border and upper surface of the lateral third of the clavicle, but also from the acromion and spine of scapula.
Inserts into the deltoid tuberosity on the lateral surface of the humerus.
Actions of each fibres of deltoid.
Anterior fibres: Flex and medially rotate arm at shoulder
Middle fibres: Abducts the arm from 15 degrees to 90 degrees.
Posterior fibres: Extend and laterally rotate the arm at the shoulder
The middle fibres of the deltoid abducts the arm from 15 to 90 degrees. Which muscle abducts the arm from 0-15 degrees?
Supraspinatus
Innervation of deltoid.
Axillary nerve (C5-C6)
What is the axilla? Why is it important?
A pyramidal space at the junction of the upper limb and the thorax. It’s a landmark and provides a passageway by which neuromuscular and muscular structures can enter and leave the upper limb.
What borders of the axilla exist?
Anterior, lateral, posterior and medial wall.
Apex and base.
What structures make up the apex of the axilla?
Lateral border of first rib
Superior border of scapula
Posterior border of the clavicle
What structures make up the lateral wall of the axilla?
Intertubercular sulcus of the humerus
What structures make up the medial wall of the axilla?
Serratus anterior, ribs and intercostal muscles.
What structures make up the posterior wall of the axilla?
Subscapularis, teres major and latissimus dorsi.
What structures make up the base of the axilla?
Axillary fascia.
How does the size and shape of the axilla change?
By the degree of arm abduction.
What passes through the axilla? (Long list)
Axillary artery Axillary vein Cords of brachial plexus Branches of brachial plexus Intercostobrachial nerve Axillary lymph nodes Biceps brachii (short head)
Why is the intercostobrachial nerve (T2) important?
Because it is a cutaneous nerve supplying the upper medial arm and part of the floor of the axilla. This means it can be a source of referred cardiac pain.
What are the three main routes by which the structures mentioned previously leave the axilla?
Inferiorly and lateral into upper limb
Via the quadrangular space (To posterior arm and shoulder area)
Via the clavipectoral triangle (opening in anterior wall of axilla)
Mnemonic for the lymph nodes of the axilla.
APICAL Anterior pectoral group Posterior subscapular group Infraclavicular (deltopectoral) group Central group Apical group Lateral group
One lymph node group receives the efferent vessels of all the other groups. Which?
Apical axillary nodes.
Where does the apical axillary nodes’ efferent vessels go?
They converge to form the subclavian lymphatic trunk.
What happens to the right subclavian lymphatic trunk?
It continues to form the right lymphatic duct and drains into the right venous angle.
What does the left subclavian lymphatic trunk drain into?
Directly into the thoracic duct and then into the left venous angle.
What are the five main artery vessels of the upper limb?
Name them proximal to distal.
Subclavian artery Axillary artery Brachial artery Radial artery Ulnar artery
Explain how the subclavian artery becomes the axillary artery.
It enters the axilla at the lateral border of the first rib and is then renamed the axillary artery.
The axillary artery can be divided into three parts. Which?
First part which is proximal to pectoralis minor.
Second part which is posterior to pectoralis minor
Third part which is distal to pectoralis minor
What are the main branches of the axillary artery?
First part: (1)
Superior thoracic artery
Second part: (2)
Thoracoacromial artery
Lateral thoracic artery
Third part: (3)
Subscapular artery
Anterior circumflex humeral artery
Posterior circumflex humeral artery
Why is it common to get avascular necrosis of the head of the humerus? How does it happen?
In case of a fracture at the surgical neck of the humerus avascular necrosis can occur.
This is due to the anterior and posterior circumflex humeral arteries which form an anastomotic network around the neck. If you then get a fracture in this region you are likely to damage these arteries and then the neck of the humerus won’t get blood supply causing necrosis.
Explain the axillary vein.
Formed at lower border of teres major from brachial veins and basilic veins. The cephalic vein also drains to the axillary vein and axillary vein also gets blood from superolateral chest wall.
Commences at inferior border of teres major and ascends through the axilla anteromedially to the axillary artery.
It becomes the subclavian vein at lateral border of first rib.
What are the major superficial veins of the upper limb?
Cephalic and basilic veins.
Where can the cephalic and basilic veins be found?
Cephalic: Runs along the pre-axial border of the upper limb
Basilic: Runs along the post-axial border of the upper limb
Origination and ascension of cephalic vein.
Dorsal venous network of the hand. Ascends anterolateral aspect of upper limb and anteriorly to elbow.
At the shoulder the cephalic vein travels between the deltoid and pectoralis major muscles and enters the axilla via the clavipectoral triangle. In the axilla the cephalic vein will drain into the first part of the axillary vein.
Origination and ascension of basilic vein.
Dorsal venous network of the hand an ascends medial aspect of upper limb.
At the Inferior border of teres major the basilic vein will move deep into the arm and pair with brachial veins from deep venous system to form axillary vein.
