Axilla and Brachial Plexus

Question 0

Important structures in the axilla:

Answer 0

• Axillary artery
• Axillary vein(s)
• Axillary lymph nodes
• Brachial plexus of nerves
• Pectoralis minor muscle
• Biceps brachii muscle
• Coracobrachialis muscle
• Axillary tail of female breast.

Question 1

Axilla “Armpit”

Answer 1

• Floor: axillary fascia and skin of armpit
• Apex: passageway for structures entering or leaving the shoulder and arm; bounded by 1 rib, clavicle and superior portion of scapula.
• Anterior wall: pectoralis major & minor muscles, clavipectoral fascia
• Posterior wall: Subscapularis, teres major, latissimus dorsi, long head of triceps brachii muscle.
• Medial wall: superior rib cage, intercostal and serratus anterior muscles.
• Lateral wall: humerus.

Question 2

Arterial supply of axilla

Answer 2

Brachiocephalic trunk -> subclavian artery -> axillary artery -> brachial artery -> radial/ulnar arteries

Question 3

Venous drainage of axilla

Answer 3

Superficial: cephalic & basilic veins
Dive down to axillary vein
Brachial veins surround brachial artery
-> Axillary v. -> subclavian v.

Question 4

Axillary lymph nodes

Answer 4

20-30 nodes divided into five groups: 
• Central nodes 
• Lateral (brachial, humeral) nodes 
• Posterior (subscapular) nodes 
• Anterior (pectoral) nodes 
• Apical (subclavian) nodes

Question 5

Brachial plexus

Answer 5

Neurovascular bundle in axilla= 
• Axillary artery 
• Axillary vein 
• Cords of brachial plexus 
=> all bound in the axillary sheath  
• Brachial plexus = ventral rami of spinal nerves C5-T1.

Question 6

Posterior triangle of neck

Answer 6

Middle scalene and trapezius
Anterior scalene
Sternocleidomastoid

Question 7

Functions of nerves in the upper limb

Answer 7

• Motor innervation to muscles
• Sensory innervation to skin & deep structures
• Vascular tone by sympathetic vasomotor nerve fibres
• Secretomotor fibres to supply sweat glands

Question 8

Brachial plexus

Answer 8

• 5 roots (ventral rami)
• 3 trunks
• 6 divisions (3 anterior, 3 posterior)
• 3 cords (named for their relationship to the axillary artery)
• 5 large terminal branches (M, A, R, M, U)

Question 9

Named nerves of the Brachial Plexus

Answer 9

Anterior rami of C5-T1
Supplies: Muscles of shoulder (superficial back muscles, anterior thoracic wall muscles)
All muscles of upper extremity.
Upper limb skin.

Question 10

Posterior cord nerves

Answer 10

• Derived from posterior divisions of all 3 trunks.
• (ULTRA)
• Upper subscapular nerve
• Lower subscapular nerve
• Thoracodorsal nerve
• Radial nerve
• Axillary nerve

Question 11

Lateral cord nerves

Answer 11

• Derived from the anterior divisions of the superior and middle trunks.
• (LML)
• Lateral pectoral nerve
• Musculocutaneous nerve
• Lateral root of median nerve

Question 12

Medial cord nerves

Answer 12

• Derived from the anterior division of the inferior trunk.
• (M4U)
• Medial pectoral nerve
• Medial cutaneous nerve of arm
• Medial cutaneous nerve of forearm
• Medial root of the median nerve
• Ulnar nerve

Question 13

Brachial Plexus: Terminal Nerves

Answer 13

• Axillary —innervates the deltoid, teres minor, and skin and joint capsule of the shoulder
• Musculocutaneous —innervates the anterior arm muscles and skin of lateral forearm
• Median —innervates the skin, most flexors and pronators in the forearm, and thenar muscles
• Ulnar —supplies the flexor carpi ulnaris, medial half of flexor digitorum profundus, most intrinsic muscles of the hand, and skin of medial aspect of hand
• Radial —innervates essentially all extensor muscles, supinators, and posterior skin of limb

Question 14

Axillary nerve (C5-C6)

Answer 14

Deltoid muscle
Teres minor muscle
Derived from posterior cord and passes posterior to humerus wrapping transversely across lateral aspect of humerus

Question 15

Musculocutaneous nerve (C5-C6-C7)

Answer 15

Coracobrachialis muscle
Brachialis muscle
Biceps brachii muscle
Derived from medial cord, pierces through
coracobrachialis, travels deep to biceps brachii / superficial to brachialis then passes
superficially to dermis to innervate lateral skin
on forearm

Question 16

Median nerve (C5-C6-C7-C8-T1)

Answer 16

Pronator teres muscle  
Flexor carpi radialis  muscle 
Palmaris longus muscle 
Flexor digitorum superficialis muscle 
Flexor digitorum profundus 
muscles to thumb and index fingers 
Flexor pollicis longus muscle 
Pronator quadratus muscle 
Lumbricals to index and middle fingers 
Thenar muscles of thumb

Question 17

Radial nerve (C5-C6-C7-C8-T1)

Answer 17

Triceps brachii muscle 
Anconeus muscle 
Brachioradialis muscle 
Extensor carpi radialis longus 
Extensor carpi radialis brevis 
Extensor digitorum 
Extensor digiti minimi 
Extensor carpi ulnaris 
Supinator 
Abductor pollicis longus 
Extensor pollicis longus 
Extensor pollicis brevis 
Extensor indicis

Question 18

Ulnar nerve (C7-C8-T1)

Answer 18

Flexor carpi ulnaris muscle 
Ulnar/lateral half of Flexor digitorum profundus muscles 
Palmar interossie 
Morsal interossei 
Adductor pollic muscle 
Palmaris brevis muscle 
Hypothenar muscles 
Lumbricals to ring and little finger 
Passes through cubital tunnel between medial epicondyle of humerus and olecranon then between heads of FCU.