Lecture 5: Axilla and Brachial plexus

Question 1

What shape is the axilla and what boundaries does it have

Answer 1

It is a truncated pyramid so it has a square base, triangular apex and 3 walls: posterior, anterior and medial

Question 2

What forms the base and apex of the axilla

Answer 2

Base of the axilla is the axillary fascia just under the armpit. It has lat dorsi as post border, pec major as ant border, serratus anterior as med border and the medial aspect of the humerus as the lateral border.

and the apex of the axilla has a triangular face with clavicle (ant), Sup border of scap (post) and 1st Rib (med) forming the sides of the triangle

Question 3

What muscles, bones and ligaments make up the ant wall of the axilla

Answer 3

Pec major + minor mostly, but also clavicle and subclavius, and costacoracoid ligament above that as well as suspensory ligament of axilla below that.

Question 4

What muscles, bones and ligaments make up the post wall of the axilla

Answer 4

Mostly subscapularis, teres major and lat dorsi muscles

Question 5

What are the contents of the axilla

Answer 5

Cords and branches of the brachial plexus and axillary artery (which go between mid and ant scalene muscle) and axillary vein (in front of ant. scalene).
Also fat and lymph nodes+lymphatics

Question 6

Describe the organisation of the brachial plexus from roots to terminal/ peripheral nerves in relation to clavicle position

Answer 6

BEFORE THE CLAVICLE
1. Brachial plexus originates from anterior rami of spinal nerves C5 to T1. These are the spinal ROOTS.
2. C5 and 6 pair together to form the superior trunk, c7 continues to form middle trunk. C8 and T1 pair together to make the inferior trunk.
AT THE CLAVICLE
3. Each trunk splits into a posterior and anterior branch called DIVISIONS
BELOW THE CLAVICLE
4. The divisions join together to form CORDS named in relation to axillary artery.
- posterior divisions from all trunks make posterior cord,
- ant divisions from middle and superior trunk make lateral cord
- ant division of inferior trunk makes medial cord
5. Five main terminal/ peripheral nerves exit from these cords with each cord splitting into two but lateral and medial cord joining back together to make 5. (listed sup to inf)
-Musculocutaneous (lat)
-Axillary (post)
-Median (lat+ medl)
-Radial (post)
-Ulnar (medl)

Question 7

At all stages of the brachial plexus. list the main off shoot/ branches

Answer 7

Roots: Long thoracic nerve from C5. C6 and C7 as well as 2 branches from C5
Trunks : 1 from sup
Divisions: none
Cords: 1 from lat, 3 from post and 3 from medl

Question 8

What are the two sensory only nerves from the medial cord and where do they give cutaneous innervation

Answer 8

Medial cutaneous nerve to the posterior arm and Medial cutaneous nerve to the posterior forearm.

Question 9

What is the 3 different nerve supplies to the anterior muscles of the arm + forearm

Answer 9

1. The musculocutaneous nerve supplies the muscles of the anterior of the arm and then becomes the lateral cutaneous nerve of the forearm which is sensory for the lateral side of the forearm
2. Median nerve supplies 3/4 of the anterior muscles of the forearm as well as the thumb and first two fingers
3. Ulnar nerve supplies the last medial 1/4 of the anterior of the forearm as well as the last two fingers of the palm.

Question 10

What action does the anterior muscles of the arm mainly do and what two cords mainly innervate this side vs posterior side

Answer 10

ANTERIOR : Mainly flexors. the nerves are all from the lateral or medial cord.
POSTERIOR: Mainly extensors. the nerves from posterior cord

Question 11

What is the 3 different nerve supplies to the posterior face of the arm + forearm

Answer 11

1. Axillary nerve supplies muscles teres minor and deltoid and is the superior lateral cutaneous nerve of the arm.
2. Radial nerve supplies all the other posterior muscles of the arm + forearm, none in hand. It also most of the sensory info for the back of the arm and forearm except for …
3. Medial cutaneous. n arm and M.C.n forearm. which do a little bubble close to the medial side.
4. Lat. Cut . n. forearm from musculocutaneous nerve as well as fingertips from the median and ulnar nerve

Question 12

Describe the arterial supply to the axilla - what is the main highway artery and what is the number of branches before reaching the end. (what are the two names of this main highway)

Answer 12

The main highway starts off as the subclavian artery which becomes brachial artery after teres major
It has one branch between the first rib and the superior border of the pec minor.
2 branches between the superior and inferior border of pec minor
3 branches between the inferior border of pec minor and teres major

Question 13

What are the anastomoses posterior scapula and what do they mean

Answer 13

They are arteries that provide an alternative pathway for blood flow around the posterior of the scapula in the event of occlusion.
These are the transverse cervical a. , suprascapular a. and the circumflex scapular a.

Question 14

What are the 5 lymph nodes of the axilla and what drains into them.

Answer 14

Base:
(lat ant) Humeral/ brachial nodes that drain the free limb
(post) subscapular nodes
(med ant) pectoral nodes drain 75% of the breast (commonly checked for metastatic cancers)

All 3 nodes drain to the central nodes in the centre of the axilla.

These then go the apical nodes on the medial border of the axilla.
Apical nodes also receive lymphatics associated with the cephalic vein.