S6) Pectoral Region, Axilla and Brachial Plexus

Question 1

What is the pectoral region?

Answer 1

The pectoral region is a region located on the anterior chest wall and contains four muscles that exert a force on the upper limb

Question 2

Identify the 4 muscles in the pectoral region

Answer 2

• Pectoralis major
• Pectoralis minor
• Serratus anterior
• Subclavius

Question 3

State the structure and function of pectoralis major

Answer 3

• Structure: most superficial muscle in the pectoral region, composed of a sternal head and a clavicular head

- Function: adduction, medial rotation, flexion (clavicular head)

Question 4

State the origin and attachments of pectoralis major

Answer 4

• 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

Question 5

Which nerve(s) innervate pectoralis major?

Answer 5

• Lateral pectoral nerve
• Medial pectoral nerve

Question 6

State the structure and function of pectoralis minor

Answer 6

• 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

Question 7

State the origins and attachments of pectoralis minor

Answer 7

• Origins: 3rd-5th ribs
• Attachments: coracoid process of the scapula

Question 8

Which nerve(s) innervates pectoralis minor?

Answer 8

Medial pectoral nerve

Question 9

State the structure and function of serratus anterior

Answer 9

• 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 90^o

Question 10

State the origins and attachments of the serratus anterior

Answer 10

• Origins: lateral aspects of ribs 1-8
• Attachments: costal surface of the medial border of the scapula

Question 11

Which nerve(s) innervate serratus anterior?

Answer 11

Long thoracic nerve

Question 12

State the structure and function of the subclavius

Answer 12

• Structure: small muscle, located directly deep to the clavicle

- Function: anchors and depresses the clavicle

Question 13

State the origins and attachments of subclavius

Answer 13

• Origins: junction of the 1st rib and its costal cartilage
• Attachments: inferior surface of the middle 1/3 of the clavicle

Question 14

Which nerve(s) innervate subclavius?

Answer 14

Nerve to subclavius

Question 15

What is the axilla region?

Answer 15

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

Question 16

What are the 6 borders of the axilla region?

Answer 16

Question 17

Which structures form the apex and base of the axilla region?

Answer 17

• Apex – lateral border of the first rib, superior border of scapula, and the posterior border of the clavicle
• Base – axillary fascia and skin

Question 18

Which structures form the lateral and medial walls of the axilla region?

Answer 18

• Lateral wall – intertubercular groove of the humerus
• Medial wall – serratus anterior and thoracic wall (ribs and intercostal muscles)

Question 19

Which structures form the anterior and posterior walls of the axilla region?

Answer 19

• Anterior wall – pectoralis major, pectoralis minor, subclavius muscles
• Posterior wall – subscapularis, teres major and latissimus dorsi

Question 20

Identify the three main routes by which structures leave the axilla

Answer 20

• Inferiorly and laterally, into the upper limb (main route)
• Through the quadrangular space
• Through the clavipectoral triangle

Question 21

What is the quadrangular space?

Answer 21

The quadrangular space is a gap in the posterior wall of the axilla, allowing access to the posterior arm and shoulder area

Question 22

Identify 2 structures which pass through the quadrangular space

Answer 22

Question 23

What is the clavipectoral triangle?

Answer 23

The clavipectoral triangle is an opening in the anterior wall of the axilla which is bound by the pectoralis major, deltoid, and clavicle

Question 24

Identify 3 structures which pass through the clavipectoral triangle

Answer 24

• Cephalic vein (enter)
• Medial pectoral nerve (exit)
• Lateral pectoral nerve (exit)

Question 25

Identify the 5 clinically important contents of the axilla region

Answer 25

- Axillary artery - Axillary vein - Brachial plexus - Biceps brachii and coracobrachialis - Axillary lymph nodes

Question 26

What is the axillary artery?

Answer 26

The **axillary artery** is the main artery supplying the upper limb

Question 27

What is the axillary vein?

Answer 27

**Axillary vein** is the main vein draining the upper limb, with contributions from the cephalic and basilic veins

Question 28

What do the axillary lymph nodes do and why are they clinically significant?

Answer 28

- 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**

Question 29

What is the brachial plexus?

Answer 29

The **brachial plexus** is a network of nerve fibres that supplies the skin and musculature of the upper limb

Question 30

Describe the formation of the brachial plexus

Answer 30

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

Question 31

Describe the course of the brachial plexus

Answer 31

- It begins in the root of the **neck** (anterior and medial scalene muscles) - It passes through the **axilla region** - It enters the **upper arm**

Question 32

How can the brachial plexus be divided?

Answer 32

The brachial plexus is divided into five parts: **roots, trunks, divisions, cords and branches** (no functional differences)

Question 33

What are the roots of the brachial plexus?

Answer 33

The **roots** refer the beginning of the brachial plexus, formed by the anterior divisions of the spinal nerves C5, C6, C7, C8 and T1

Question 34

What are the trunks of the brachial plexus

Answer 34

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

Question 35

What are the divisions of the brachial plexus?

Answer 35

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)

Question 36

What are the cords of the brachial plexus?

Answer 36

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)

Question 37

What are the 5 major branches of the brachial plexus?

Answer 37

Question 38

Identify the roots of the musculocutaneous nerve

Answer 38

C5, C6, C7

Question 39

Describe the motor and sensory functions of the musculocutaneous nerve

Answer 39

- **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

Question 40

Identify the roots of the axillary nerve

Answer 40

C5 and C6

Question 41

Describe the motor and sensory functions of the axillary nerve

Answer 41

- **Motor functions:** innervates the teres minor and deltoid muscles - **Sensory functions:** innervates the inferior region of the deltoid (regimental badge area)

Question 42

Identify the roots of the median nerve

Answer 42

C6 – T1 (also, contains fibres from C5 in some individuals)

Question 43

Describe the motor and sensory functions of the median nerve

Answer 43

- **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

Question 44

Identify the roots of the radial nerve

Answer 44

C5-C8 and T1

Question 45

Describe the motor and sensory functions of the radial nerve

Answer 45

- **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

Question 46

Identify the roots of the ulnar nerve

Answer 46

C8 and T1

Question 47

Describe the motor and sensory functions of the ulnar nerve

Answer 47

- **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

Question 48

In terms of the branches of the brachial plexus, what are the motor compartments of the upper arm?

Answer 48

Question 49

What is long thoracic nerve palsy?

Answer 49

- **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

Question 50

When does long thoracic nerve palsy commonly occur?

Answer 50

**Long thoracic nerve palsy** commonly occurs when upper limb is stretched violently (traction injuries)

Question 51

What is the clinical significance of axillary lymph nodes?

Answer 51

Approximately 75% of lymph from the breast drains into the **axilla lymph nodes**, so can be biopsied if breast cancer is suspected

Question 52

What is axillary clearance and what are its associated risks?

Answer 52

- **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**

Question 53

What is Erb's Palsy?

Answer 53

**- 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

Question 54

Identify the various nerves affected and muscles paralysed in Erb's palsy

Answer 54

- **Nerves affected:** musculocutaneous, axillary, suprascapular and nerve to subclavius - **Muscles paralysed:** supraspinatus, infraspinatus, subclavius, biceps brachii, brachialis, coracobrachialis, deltoid and teres minor

Question 55

Identify the motor functions weakened and the sensation lost in Erb's palsy

Answer 55

**- Motor functions:** shoulder abduction, lateral rotation, supination, shoulder flexion **- Loss of sensation:** lateral side of arm

Question 56

When does Erb's palsy commonly occur?

Answer 56

**Erb’s palsy** commonly occurs where there is excessive increase in the angle between the neck and shoulder (difficult birth or shoulder trauma)

Question 57

What is Klumpke's Palsy?

Answer 57

- **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

Question 58

Identify the 2 nerves affected by Klumpke's palsy

Answer 58

- Ulnar nerve - Median nerve

Question 59

Identify the muscles paralysed and describe sensation lost in Klumpke's palsy

Answer 59

- **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

Question 60

When does Klumpke's palsy commonly occur?

Answer 60

**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)