Axilla, brachial plexus and anterior arm muscles

Question 1

What makes up the anterior wall of the axilla?

Answer 1

Pectoralis major and pectoralis minor

Question 2

What makes up the posterior wall of the axilla?

Answer 2

Subscapularis, teres major and latissimus dorsi muscles

Question 3

What makes up the lateral wall of the axilla?

Answer 3

Upper end of the humerus with the biceps brachii and the coracobrachialis muscles.

Question 4

What makes up the medial wall of the axilla?

Answer 4

The serratus anterior muscle covering the ribs and intercostal spaces.

Question 5

What makes up the apex of the axilla?

Answer 5

Formed by the first rib medially with the clavicle in front and the scapula behind. It is the channel of communication between the posterior triangle of the neck and the axilla.

Question 6

What makes up the base of the axilla?

Answer 6

Skin and fascia extending between the chest wall and the arm.

Question 7

What is contained within the axilla?

Answer 7

Fat and lymph nodes
Axillary artery which is the major artery supplying the upper limb
Axillary vein; the major venous drainage of the arm
Brachial plexus – the nerve plexus supplying the limb

Question 8

What is the axillary sheath?

Answer 8

The axillary sheath is a fascial sheath that is a prolongation of the fascia covering the muscles in the posterior triangle of the neck (the prevertebral fascia).

Question 9

What are the axillary lymph nodes?

Answer 9

The lymph nodes in the axilla drain lymph from the upper limb, chest wall (both front and back) and the abdominal wall as far as the umbilicus. Cancers can spread to other parts of the body through lymph channels and the axillary lymph nodes are commonly involved in cancerous spread particularly from the breast.

Question 10

Where are the branches of the axillary artery?

Answer 10

There is one branch of the axillary artery above pectoralis minor, two behind and three below.

Question 11

How is the brachial plexus relative to the axillary artery?

Answer 11

Deep to the pectoralis minor muscle lies the axillary artery and the cords of the brachial plexus which run along the artery. The cords are split up into lateral, medial and posterior according to their position in relation to the axillary artery.

Question 12

What are all the arteries of the arm and forearm?

Answer 12

Begins as the subclavian artery, branching directly from the aorta (left side) or from the brachiocephalic trunk (right side).
At the lateral border of the first rib, the subclavian artery enters the axilla – and is renamed the axillary artery.
At the lower border of the teres major muscle, the axillary artery is renamed the brachial artery.
The brachial artery proper descends down the arm. As it moves through the cubital fossa, underneath the bicipital aponeurosis, the brachial artery terminates by bifurcating into the radial and ulnar arteries.

Question 13

What is the brachial plexus?

Answer 13

A network of nerves that supply the skin and musculature of the upper limb. Begins in the root of the neck, passes through the axilla and runs through the entire upper extremity.
Made up of the anterior rami of spinal nerves C5, C6, C7, C8 and T1.

Question 14

What are the roots of the brachial plexus?

Answer 14

Anterior rami of spinal nerves C5, C6, C7, C8 and T1. At each vertebral level, paired spinal nerves arise and leave the spinal cord via the intervertebral foramina.

Question 15

What are the trunks of the brachial plexus?

Answer 15

The roots converge to form 3 trunks. Superior trunk is made up of C5 and C6. Middle trunk is a continuation of C7. Inferior trunk is made up of C8 and T1.

Question 16

What are the divisions of the brachial plexus?

Answer 16

Each trunk divides into two branches within the posterior triangle of the neck. One division moves anteriorly (3 nerve fibres) and the other posteriorly (3 nerve fibres).

Question 17

What are the cords of the brachial plexus?

Answer 17

They combine together to form three cords, named by their position relative to the axillary artery.
The lateral cord is made up of the anterior divisions of the superior and middle trunks.
The posterior cord is made up of the posterior divisions of the superior, middle and inferior trunks. The medial cord is made up of just the anterior division of the inferior trunk.

Question 18

What are the five branches of the brachial plexus?

Answer 18

Musculocutaneous nerve (C5-C7) - innervates biceps brachii, brachialis, coracobrachialis.

Axillary nerve (C5-C6) - innervates deltoid, teres minor and skin over the inferior portion of the deltoid

Median nerve (C6-T1) - innervates the flexors of the forearm but not flexor carpi ulnaris or the medial half of flexor digitorum profundus
LLOAF - lateral lumbricals, opponens pollicis, abductor pollicis brevis, flexor pollicis brevis.

Radial nerve (C5-T1) - innervates triceps brachii, brachioradialis, the extensors of the forearm, cutaneous innervation to the skin of the upper limb

Ulnar nerve (C8-T1) - innervates flexor carpi ulnaris, medial half of flexor digitorum profundus, hypothenar muscles, medial two lumbricals, adductor pollicis, palmar and dorsal interossei, palmaris brevis

Question 19

What is the cutaneous innervation of the hand?

Answer 19

Median nerve - Cutaneous innervation of palmar thumb, 2, 3 and half of 4 as well as dorsum tips of thumb, 2, 3 and half of 4.
Radial nerve - cutanaeous innervation of lateral palmar thumb and dorsum thumb, 2, 3 and half of 4 (minus tips).
Ulnar nerve - Cutaneous innervation of palmar and dorsum half of 4 and 5.

Question 20

What is the cubital fossa?

Answer 20

The cubital fossa lies in front of the elbow. Superficial veins here are often used for intravenous injections and taking blood samples. The bicipital aponeurosis separates the superficial veins (variable in their patterns) from the brachial artery and the median nerve.

Question 21

What is the lateral border of the cubital fossa?

Answer 21

Medial border of the brachioradialis

Question 22

What is the medial border of the cubital fossa?

Answer 22

Lateral border of the pronator teres

Question 23

What is superior border of the cubital fossa?

Answer 23

Imaginary line between the epicondyles

Question 24

What is the floor of the cubital fossa?

Answer 24

Proximally by the brachialis, distally by the supinator

Question 25

What is the roof of the cubital fossa?

Answer 25

Skin and fascia, and is reinforced by the bicipital aponeurosis

Question 26

What is the contents of the cubital fossa?

Answer 26

Radial nerve passing underneath the brachioradialis
Biceps brachii attaching to the radial tuberosity
Brachial artery, which bifurcates at the apex of the cubital fossa into the radial and ulnar arteries
Median nerve, leaves the cubital fossa between the heads of the pronator teres.

Question 27

What are the major features of the biceps brachii?

Answer 27

Two-headed muscle
Long head originates from the supraglenoid tubercle of the scapula.
Short head originates from the coracoid process of the scapula.
Insert distally into the radial tuberosity via the bicipital aponeurosis.
Acts to supinate the forearm and flex the arm at the elbow and the shoulder.
Innervated by the musculocutaneous nerve.

Question 28

What are the major features of the Coracobrachilis?

Answer 28

Lies deep to the biceps brachii.
Originates from the coracoid process of the scapula.
Passes through the axilla.
Attaches onto the medial surface of the humeral shaft.
Acts to flex the arm at the shoulder, and weak adduction.
Innervated by the musculocutaneous nerve.

Question 29

What are the major features of the Brachialis?

Answer 29

Lies deep to the biceps brachii. Forms the floor of the cubital fossa.
Originates from the medial and lateral surfaces of the humeral shaft.
Inserts onto the ulnar tuberosity.
Acts to flex at the elbow.
Innervated by the musculocutaneous nerve.

Question 30

What are the major features of the triceps brachii?

Answer 30

Made up of three heads, with the medial head being deep to the other two.
Long head originates from the infraglenoid tubercle of the scapula.
Lateral head originates from the humerus, superior to the radial groove.
Medial head originates from the humerus, inferior to the radial groove.
Insert onto the olecranon of the ulna.
Acts to extend at the elbow.
Innervated by the radial nerve.

Question 31

What is Erb’s palsy?

Answer 31

If the upper one or two roots of the brachial plexus are damaged then there will be a specific pattern of motor paralysis. The external rotators of the shoulder are paralysed so the humerus is internally rotated and the extensors of the wrist are paralysed. The wrist is held flexed. AKA ‘waiter’s tip’ palsy.

Question 32

What is Klumpke palsy?

Answer 32

The lower one or two roots of the brachial plexus are damaged. All the small muscles of the hand are paralysed and if the C8 is also involved some of the forearm muscles are affected.

Question 33

What is Horner’s syndrome?

Answer 33

The T1 nerve root forms the lower root of the brachial plexus; it also carries fibres of the sympathetic nervous system which are destined to supply the face. Damage to these sympathetic fibres will result in drooping of the eyelid (ptosis), lack of sweating on the face (anhidrosis) and a constricted pupil (miosis).

Question 34

Where do the roots of the brachial plexus arise from?

Answer 34

From the anterior rami of C5 to T1.

These nerves emerge from the relevant intervertebral foramina in the neck.

Question 35

Where do the cords of the brachial plexus form?

Answer 35

The formation of the cords is found under Pectoralis minor.

Question 36

When are nerves vulnerable?

Answer 36

1. They are superficial.
2. They lie on bone.
3. They pass behind structures i.e. ligaments or run between 2 heads of a muscle.

Question 37

What nerve damage can be caused by a mid-shaft fracture of the humerus?

Answer 37

The Radial nerve lies on the back of the humerus.
A mid shaft fracture could damage the radial nerve.
Extension of the elbow may still be possible as the radial nerve comes into triceps high but extension of the wrist will not be possible. Only the flexor compartment is still functioning, hence wrist drop.

Question 38

What nerve damage can occur as a result of a patient cutting their wrists?

Answer 38

The Ulnar nerve lies over the Flexor retinaculum, at the wrist and therefore is more superficial when compared to the median nerve which runs under the retinaculum. In attempts at cutting the wrists the more superficial ulnar is more vulnerable to being cut.

Question 39

Which muscles do the peripheral nerves run between?

Answer 39

As each of the peripheral nerves enters the forearm they run between 2 heads of a muscle.
Median - 2 heads of pronator teres
Ulnar - 2 heads of FCU
Radial- 2 heads of supinator
If the muscles become inflamed-compression injuries result.

Question 40

Why might a tumour in the apex of the lung affect the hand?

Answer 40

A tumour growing in the apex of the lung may present with problems in the hand. The tumour has invaded the lower trunk of the brachial plexus. The lower trunk would go on to give you the Ulnar nerve which is mainly involved with the small muscles of the hand.