Anatomy dissection notes 9

Question 1

What is the axilla ?

Answer 1

• It is the pyramidal space inferior to the shoulder joint and just superior to the armpit
• It is an important “gateway” for structures entering or leaving the upper limb e.g. arteries, veins, nerves and lymphatics.

Question 2

What are the different borders and shape of the axilla (don’t want the muscles yet)?

Answer 2

It has a pyramidal type structure so has:

• Apex
• Lateral and medial walls
• Anterior and posterior walls

Question 3

What are the anterior and posterior borders of the axilla (specifically looking for the muscles here)?

Answer 3

• Anterior wall - Pectoralis major and the underlying pectoralis minor and the subclavius muscles.
• Posterior wall – Formed by the subscapularis, teres major and latissimus dorsi.

Question 4

What is the function of the pectoralis major ?

Answer 4

One of the main muscles of climbing and also an excessory muscle of respiration

Question 5

Where can pulsations of the subclavian artery be felt ?

Answer 5

As it crosses the first rib

Question 6

When does the subclavian artery become the axillary artery ?

Answer 6

At the lateral border of the first rib

Question 7

What are the main contents within the axilla ?

Answer 7

• Axillary artery
• Axillary vein
• Brachial plexus
• Axillary lymph nodes

Question 8

What spinal nerves (anterior rami) make up the brachail plexus ?

Answer 8

C5-T1

Question 9

Describe the changes in the brachial plexus going from proximal to distal

Answer 9

Goes from Roots ===> Trunks ===> Divisions ===> Cords ===> Named nerves

Think - Really Tired, Don’t Care Now

Question 10

How does the brachail plexus go from the root values to trunks ?

Answer 10

The anterior rami (C5-T1) mix to form superior, middle and inferior trunks

Question 11

What nerve root values make up the different trunks of the brachial plexus ?

Answer 11

• Superior trunk = C5&6
• Middle trunk = C7
• Inferior trunk = C8 & T1

Question 12

In terms of divisions what does each trunk give off and why is this relevant ?

Answer 12

Each trunk gives off an anterior and posterior division - relevant as these divisions branch of and join to form the cords

Question 13

What are the different cords of the brachial plexus and how are they named?

Answer 13

• They are named according to there relationship to the axillary artery
• You have the medial, lateral and posterior cords

Question 14

What divisions forms the different cords ?

Answer 14

• Medial cord = a direct continuation of the anterior division of the inferior trunk
• Lateral cord = formed from the anterior divisions of the superior and middle trunks
• Posterior cord = formed from the posterior divisions of all three trunks

Question 15

The cords then branch into the named nerves what are the different named nerves formed?

Answer 15

1. Ulnar
2. Musculocutaneous
3. Axillary
4. Radial
5. Median

Question 16

How are each of the named nerves formed ?

Answer 16

• The ulnar nerve continues directly from the medial cord
• The musculocutaneous nerve continues directly from the lateral cord
• The posterior cord divides into the axillary nerve and radial nerve
• The medial and lateral cords both contribute the formation of the median nerve

Question 17

What is the most lateral and what is the most medial of the named nerves in the brachial plexus ?

Answer 17

• Most lateral is the musculocutaneous nerve
• Most medial is the ulnar nerve

Question 18

What does the musculocutaneous nerve innervate ?

Answer 18

• Coracobrachialis muscle
• Biceps brachii
• Brachialis muscle

Question 19

Describe the route of the axillary and radial nerves and when they are vulnerable to injury due to there routes

Answer 19

• Both axillary and radial pass into the posterior compartment of the arm
• Axillary nerve lies superior to the radial
• Axillary nerve wraps around the surgical neck of the humerus - making it vulnerable in shoulder dislocations and fractures to the neck of the humerus
• Radial nerve wraps around the mid-shaft of the humerus - making it vulnerable to injury in mid-shaft fractures

Question 20

What is the characteristic appearance of the median nerve ?