Axillary Region & Brachial Plexus

Functional Anatomy 2

axilla

• a region of transition

• pyramid shaped area between the pectoral region and the brachium

• provides a channel by which the axillary a/v and brachial plexus pass through to get to the upper extremity

apex

between the clavicle, 1st rib and scapula

base

axillary skin fold, armpit

anterior wall

pectoralis major and pectoralis minor muscles

lateral wall

humerus

medial wall

serratus anterior muscle

posterior wall

subscapularis, teres major, latissimus dorsi muscles

contents of axilla

• axillary artery

• axillary vein

• brachial plexus

• lymphatics

• lots of variability in this region

suprascapular notch/foramen borders

inferior: suprascapular notch

superior: superior transverse scapular ligament (suprascapular ligament)

• converts the notch into a foramen

suprascapular notch/foramen contents

suprascapular n.

• through the foramen, inferior to the ligament

• to supraspinatus and infraspinatus muscles

suprascapular a.

• superior to the ligament

quadrangular space borders

superior: inferior margin teres minor/subscapularis

inferior: superior margin teres major

lateral: surgical neck of humerus

medial: lateral margin long-head triceps brachii

quadrangular space contents

• axillary nerve (to deltoid and teres minor muscles)

• posterior humeral circumflex a.

triangular space borders

superior: inferior margin teres minor/subscapularis

inferior: superior margin teres major

lateral: medial margin long-head triceps brachii

triangular space contents

circumflex scapular a.

triangular interval borders

superior: inferior margin teres major

medial: lateral margin of long-head triceps brachii

lateral: shaft of humerus

triangular interval contents

radial n. (to posterior brachium and posterior antebrachium)

deep brachial a. (profunda brachii a.)

quadrangular space

• teres minor, teres major, humerus, triceps brachii

• axillary nerve, posterior humeral circumflex artery

triangular space

• teres minor, teres major, triceps brachii

• circumflex scapular artery

triangular interval

• teres major, triceps brachii, humerus

• radial nerve, deep brachial artery

blood supply upper extremity

heart (left ventricle)

aorta (aortic arch)

brachiocephalic trunk/artery

subclavian artery

axillary artery

brachial artery

subclavian artery

begins:

• R: division of brachiocephalic trunk into R subclavian a. and R common carotid a.

• L: third branch of aortic arch

three parts:

1. origin to medial edge anterior scalene

• vertebral a.

• internal thoracic a.

• thyrocervical trunk → suprascapular a.

2. posterior to anterior scalene

• no branches

3. lateral edge anterior scalene to lateral edge 1st rib

• dorsal scapular a.

ends:

• lateral edge of 1st rib (both)

axillary artery

divided into 3 parts by pectoralis minor muscle

• part 1: lateral border of 1st rib to superior/medial border of pectoralis minor muscle

• part 2: deep to pectoralis minor muscle

• part 3: between inferior/lateral border of pectoralis minor muscle and inferior border of teres major muscle

axillary artery 1st part

1 branch, superior thoracic artery

axillary artery 2nd part

2 branches

• thoracoacromial trunk (with branches)

  • acromial, clavicular, pectoral, deltoid

• lateral thoracic artery

axillary artery 3rd part

3 branches

• subscapular artery (with branches)

  • circumflex scapular a.

  • thoracodorsal a.

• anterior circumflex humeral a.

• posterior circumflex humeral a.

anterior humeral circumflex artery

• smaller than posterior humeral circumflex artery

• passes anterior to the surgical neck of the humerus

• anastomoses with the posterior humeral circumflex artery

posterior humeral circumflex artery

• larger than anterior humeral circumflex artery

• travels through quadrangular space with the axillary nerve

• anastomoses with anterior humeral circumflex artery

scapular anastamoses

from subclavian artery

• suprascapular artery → superior to transverse scapular ligament

• dorsal scapular artery → medial border of scapula

from axillary artery (subscapular branch)

• circumflex scapular artery → lateral border of scapula

veins

generally matched with arteries

• axillary, subclavian

superficial upper extremity veins

basilic, cephalic, median cubital, dorsal venous network (arch)

basilic vein

travels medial to biceps brachii, joins with brachial to form axillary

cephalic vein

travels lateral to biceps brachii, between anterior deltoid and pectoralis major, drains into axillary

median cubital vein

oblique segment of vein that connects basilic and cephalic veins at anterior elbow

dorsal venous network (arch)

joining of cephalic and basilic veins on dorsal hand

brachial plexus

all muscles of the upper extremity are supplied by nerves from the

variability

_______ in specific organization and branching of the nerves

C5-T1

ventral rami of spinal segments

• roots pass between the middle and anterior scalene

brachial plexus trunks

roots/rami come together, superior to clavicle

• upper trunk: C5 and C6

• middle trunk: C7

• lower trunk: C8-T1

brachial plexus divisions

• separation of each trunk into anterior and posterior “divisions”

• divisions are posterior to the clavicle

• no named nerves/branches come off the divisions directly

brachial plexus cords

• anterior divisions from the upper and middle trunks come together to form the lateral cord

• anterior division from the lower trunk forms the medial cord

• all three posterior divisions come together to form the posterior cord

• named by their location in relation to the axillary artery

brachial plexus (terminal) branches

5 terminal branches (nerves) from the cords

• lateral cord

  • musculocutaneous n.

  • lateral root of median n.

• posterior cord

  • axillary n.

  • radial n.

• medial cord

  • ulnar n.

  • medial root of median n.

• other nerves branch from other parts of the plexus

musculocutaneous nerve

C5, C6, C7

• from lateral cord

• pierces coracobrachialis muscle

• travels deep to biceps brachii, superficial to brachialis muscle

• emerges superficially at distal lateral biceps as lateral antebrachial cutaneous n.

median nerve

C6-T1

• travels medial/deep to biceps brachii, medial to distal tendon of biceps brachii

• medial and lateral cord

• innervates anterior compartment of the forearm except 2 muscles

  • flexor carpi ulnaris and medial half of flexor digitorum profundus

• innervates 5 intrinsic muscles of the hand

ulnar nerve

C8-T1

• medial cord

• travels medial to biceps brachii, posterior to medial epicondyle of humerus

• innervates the other two muscles of the anterior forearm

  • flexor carpi ulnaris and medial half of flexor digitorum profundus

• innervates hypothenar muscles of the hand, adductor pollicis, lumbricals 3 and 4, dorsal/palmar interossei

axillary nerve

C5-C6

• posterior cord

• travels to posterior arm through the quadrangular space, wraps around surgical neck of humerus with the posterior humeral circumflex artery

• innervates deltoid and teres minor muscles, cutaneous to upper lateral brachium

radial nerve

C5-T1

• posterior cord (largest branch!)

• travels to posterior arm through the triangular interval with the deep brachial artery, continues along posterior humerus in the radial groove (deep to triceps brachii)

• innervates (including its more distal branches) all muscles of the posterior brachium and posterior antebrachium (extensors)

supraclavicular branches of brachial plexus

dorsal scapular nerve, suprascapular nerve, nerve to subclavius, long thoracic nerve

dorsal scapular nerve

• off C5 nerve root

• travels posterior to levator scapulae and rhomboids

suprascapular nerve

• off superior trunk (C5-C6)

• travels posteriorly through the suprascapular foramen to supraspinatus and infraspinatus

• travels with suprascapular artery

nerve to subclavius

off superior trunk (C5-C6)

long thoracic nerve

C5-C7 roots

• descends inferior along the lateral thorax to serratus anterior muscle

infraclavicular branches of brachial plexus

lateral cord, medial cord, posterior cord

lateral pectoral nerve

C5-C7

• travels superior to pectoralis minor with the pectoral branch of the thoracoacromial artery, then to pectoralis major

medial brachial cutaneous nerve

C8-T1

• innervate the medial skin of the arm

medial antebrachial cutaneous nerve

C8-T1

• innervate the medial skin of the arm

medial pectoral n.

C8-T1

• travels through pectoralis minor to innervate pectoralis minor and pectoralis major

upper subscapular nerve

C5

• innervates subscapularis muscle

lower subscapular nerve

C6

• innervates subscapularis and teres major

thoracodorsal nerve

C6-C8

• travels interiorly to innervate latissimus dorsi muscle

upper extremity cutaneous innervation map

upper extremity dermatome innervation map