S6) Pectoral Region, Axilla and Brachial Plexus Flashcards
What is the pectoral region?
The pectoral region is a region located on the anterior chest wall and contains four muscles that exert a force on the upper limb
Identify the 4 muscles in the pectoral region
- Pectoralis major
- Pectoralis minor
- Serratus anterior
- Subclavius
State the structure and function of pectoralis major
- Structure: most superficial muscle in the pectoral region, composed of a sternal head and a clavicular head
- Function: adduction, medial rotation, flexion (clavicular head)
State the origin and attachments of pectoralis major
- Origins:
I. Clavicular head – anterior surface of medial clavicle
II. Sternocostal head – anterior surface of sternum, superior six costal cartilages and aponeurosis of external oblique muscle
- Attachments: intertubercular sulcus of the humerus
Which nerve(s) innervate pectoralis major?
- Lateral pectoral nerve
- Medial pectoral nerve
State the structure and function of pectoralis minor
- Structure: lies deep to pectoralis major, forms part of the anterior wall of the axilla region
- Function: stabilises the scapula by drawing it anteroinferiorly against the thoracic wall
State the origins and attachments of pectoralis minor
- Origins: 3rd-5th ribs
- Attachments: coracoid process of the scapula
Which nerve(s) innervates pectoralis minor?
Medial pectoral nerve
State the structure and function of serratus anterior
- Structure: located laterally in the chest wall, forming the medial border of the axilla region
- Function: rotates the scapula, allowing the arm to be raised over 90o
State the origins and attachments of the serratus anterior
- Origins: lateral aspects of ribs 1-8
- Attachments: costal surface of the medial border of the scapula
Which nerve(s) innervate serratus anterior?
Long thoracic nerve
State the structure and function of the subclavius
- Structure: small muscle, located directly deep to the clavicle
- Function: anchors and depresses the clavicle
State the origins and attachments of subclavius
- Origins: junction of the 1st rib and its costal cartilage
- Attachments: inferior surface of the middle 1/3 of the clavicle
Which nerve(s) innervate subclavius?
Nerve to subclavius
What is the axilla region?
The axilla region is an area that lies underneath the shoulder joint, at the junction of the upper limb and the thorax, acting as a passageway for neurovascular and muscular structures
What are the 6 borders of the axilla region?
Which structures form the apex and base of the axilla region?
- Apex – lateral border of the first rib, superior border of scapula, and the posterior border of the clavicle
- Base – axillary fascia and skin
Which structures form the lateral and medial walls of the axilla region?
- Lateral wall – intertubercular groove of the humerus
- Medial wall – serratus anterior and thoracic wall (ribs and intercostal muscles)
Which structures form the anterior and posterior walls of the axilla region?
- Anterior wall – pectoralis major, pectoralis minor, subclavius muscles
- Posterior wall – subscapularis, teres major and latissimus dorsi
Identify the three main routes by which structures leave the axilla
- Inferiorly and laterally, into the upper limb (main route)
- Through the quadrangular space
- Through the clavipectoral triangle
What is the quadrangular space?
The quadrangular space is a gap in the posterior wall of the axilla, allowing access to the posterior arm and shoulder area
Identify 2 structures which pass through the quadrangular space
What is the clavipectoral triangle?
The clavipectoral triangle is an opening in the anterior wall of the axilla which is bound by the pectoralis major, deltoid, and clavicle
Identify 3 structures which pass through the clavipectoral triangle
- Cephalic vein (enter)
- Medial pectoral nerve (exit)
- Lateral pectoral nerve (exit)
Identify the 5 clinically important contents of the axilla region
- Axillary artery
- Axillary vein
- Brachial plexus
- Biceps brachii and coracobrachialis
- Axillary lymph nodes
What is the axillary artery?
The axillary artery is the main artery supplying the upper limb
What is the axillary vein?
Axillary vein is the main vein draining the upper limb, with contributions from the cephalic and basilic veins
What do the axillary lymph nodes do and why are they clinically significant?
- The axillary lymph nodes filter lymph that has drained from the upper limb and pectoral region
- In women, axillary lymph node enlargement is a non-specific indicator of breast cancer
What is the brachial plexus?
The brachial plexus is a network of nerve fibres that supplies the skin and musculature of the upper limb
Describe the formation of the brachial plexus
The plexus is formed by the anterior rami (divisions) of the cervical spinal nerves C5, C6, C7 and C8, and the first thoracic spinal nerve, T1
Describe the course of the brachial plexus
- It begins in the root of the neck (anterior and medial scalene muscles)
- It passes through the axilla region
- It enters the upper arm
How can the brachial plexus be divided?
The brachial plexus is divided into five parts: roots, trunks, divisions, cords and branches (no functional differences)
What are the roots of the brachial plexus?
The roots refer the beginning of the brachial plexus, formed by the anterior divisions of the spinal nerves C5, C6, C7, C8 and T1
What are the trunks of the brachial plexus
At the base of the neck, the roots converge to form three trunks:
- Superior trunk – a combination of C5 and C6 roots
- Middle trunk – a continuation of C7
- Inferior trunk – a combination of C8 and T1 roots
What are the divisions of the brachial plexus?
Within the posterior triangle of the neck, each trunk divides into two branches:
- The anterior division (3 nerve fibres)
- The posterior division (3 nerve fibres)
What are the cords of the brachial plexus?
Once the anterior and posterior divisions enter the axilla, they combine to form three cords:
- The lateral cord (anterior divisions of superior & middle trunk)
- The posterior cord (posterior divisions of all trunks)
- The medial cord (anterior division of inferior trunk)
What are the 5 major branches of the brachial plexus?
Identify the roots of the musculocutaneous nerve
C5, C6, C7
Describe the motor and sensory functions of the musculocutaneous nerve
- Motor functions: innervates the brachialis, biceps brachii and coracobrachialis muscles
- Sensory functions: innervates the lateral half of the anterior forearm, and a small lateral portion of the posterior forearm
Identify the roots of the axillary nerve
C5 and C6
Describe the motor and sensory functions of the axillary nerve
- Motor functions: innervates the teres minor and deltoid muscles
- Sensory functions: innervates the inferior region of the deltoid (regimental badge area)
Identify the roots of the median nerve
C6 – T1 (also, contains fibres from C5 in some individuals)
Describe the motor and sensory functions of the median nerve
- Motor functions: innervates most of the flexor muscles in the forearm, the thenar muscles and the two lateral lumbricals for the index & middle fingers
- Sensory functions: innervates the lateral part of the palm, the lateral 3 ½ fingers on the palmar surface
Identify the roots of the radial nerve
C5-C8 and T1
Describe the motor and sensory functions of the radial nerve
- Motor functions: innervates the triceps brachii, and the extensor muscles in the posterior compartment of the forearm
- Sensory functions: innervates the posterior aspect of the arm and forearm, and the posterior, lateral aspect of the hand
Identify the roots of the ulnar nerve
C8 and T1
Describe the motor and sensory functions of the ulnar nerve
- Motor functions: innervates the muscles of the hand (apart from the thenar muscles and two lateral lumbricals), flexor carpi ulnaris and medial half of flexor digitorum profundus
- Sensory functions: innervates the anterior and posterior surfaces of the medial 1 ½ fingers, and the associated palm area
In terms of the branches of the brachial plexus, what are the motor compartments of the upper arm?
What is long thoracic nerve palsy?
- Long thoracic nerve palsy is a condition characterized by pain and loss of shoulder movement due to damage/injury of the long thoracic nerve
- It presents with winged scapula as the serratus anterior is paralysed and the scapula is no longer held against the ribcage so protrudes out the back
When does long thoracic nerve palsy commonly occur?
Long thoracic nerve palsy commonly occurs when upper limb is stretched violently (traction injuries)
What is the clinical significance of axillary lymph nodes?
Approximately 75% of lymph from the breast drains into the axilla lymph nodes, so can be biopsied if breast cancer is suspected
What is axillary clearance and what are its associated risks?
- Axillary clearance is a procedure wherein the axillary nodes are removed to prevent breast cancer from spreading
- During this procedure, the long thoracic nerve may become damaged, resulting in winged scapula
What is Erb’s Palsy?
- Erb’s palsy is a condition resulting in the paralysis of the arm caused by injury to the upper brachial plexus (C5-C6)
- It presents with waiter’s tip: affected limb hangs limply, medially rotated by pectoralis major and pronated due to the loss of biceps brachii
Identify the various nerves affected and muscles paralysed in Erb’s palsy
- Nerves affected: musculocutaneous, axillary, suprascapular and nerve to subclavius
- Muscles paralysed: supraspinatus, infraspinatus, subclavius, biceps brachii, brachialis, coracobrachialis, deltoid and teres minor
Identify the motor functions weakened and the sensation lost in Erb’s palsy
- Motor functions: shoulder abduction, lateral rotation, supination, shoulder flexion
- Loss of sensation: lateral side of arm
When does Erb’s palsy commonly occur?
Erb’s palsy commonly occurs where there is excessive increase in the angle between the neck and shoulder (difficult birth or shoulder trauma)
What is Klumpke’s Palsy?
- Klumpke’s palsy is a condition resulting in the paralysis of the muscles of the forearm and hand caused by injury to the lower brachial plexus
- The hand presents with a clawed appearance as the MCP joints are hyperextended and the IP joints are flexed
Identify the 2 nerves affected by Klumpke’s palsy
- Ulnar nerve
- Median nerve
Identify the muscles paralysed and describe sensation lost in Klumpke’s palsy
- Muscles paralysed: small muscles of the hand (flexor muscles in the forearm are supplied by the ulna and median nerves, but are innervated by different roots)
- Loss of sensation: medial side of arm
When does Klumpke’s palsy commonly occur?
Klumpke’s palsy commonly results from excessive abduction of the arm e.g person catching a branch as they fall from a tree (lower incidence than Erb’s palsy)
