AXILLA & BRACHIAL PLEXUS

Question 1

In what two ways is the upper limb connected to the trunk?

Answer 1

Sternoclavicular Joint (bony connection) and Back Muscles (muscular connection). Muscles that help attach the limb to the axial skeleton are: latissimus dorsi, trapezius, levator scapula, rhomboids

Question 2

Describe the walls of the Axilla.

Answer 2

Anterior wall - pectoralis major and minor
Posterior wall - subscapularis, teres major, latissimus dorsi
Lateral wall - humerus
Medial wall - serratus anterior

Question 3

What nerve innervates the pectoralis minor? What of the major?

Answer 3

Pec minor innervated by medial pectoral nerve. Pec major innervated by both medial and lateral pectoral nerves.

Question 4

Describe the general myotome layout of the upper limb.

Answer 4

C5/6 is in the shoulder, C6/7 in the arm, C7/8 in the forearm, C8/T1 in the hand.

Question 5

Describe the dermatome layout of the upper limb.

Answer 5

Down the lateral side of the limb and back up the medial side, the spinal nerve roots flow from most superior to inferior of the brachial plexus. For instance, the C6 dermatome runs along the lateral side of the limb up to the thumb (radial side of the hand).

Question 6

Define segmental innervation.

Answer 6

Allows for the intermingling of fibers in the brachial plexus. Receiving input from several spinal roots to provide output at multiple levels.
“Not every segment shown in the terminal nerve innervates EVERY muscle that’s innervated by that terminal nerve.”

Question 7

Why are there divisions of the brachial plexus?

Answer 7

Muscles are divided into posterior and anterior groups therefore nerves must be divided likewise. Flexors on the anterior and Extensors on the posterior compartments of the limb.

Question 8

How does the position of plexus lesions affect the upper limb?

Answer 8

Post-plexus lesions (below the clavicle) cause sensory LOSS and paralysis of muscle innervated by specific nerves. Pre-plexus lesions (above the clavicle) lead to sensory DEFICIT of affected dermatomes and muscle weakness

Question 9

Describe Thoracic Outlet Syndrome.

Answer 9

The presence of an extra-cervical rib or a C8/T1 lesion compresses the LOWER segments. This can lead to pain radiating down the medial side of the arm, forearm and hand. Prolonged effects also include wasted right thenar eminence and loss of radial pulse when limb is pulled down.

Question 10

What muscle does the Lateral Pectoral nerve innervate? What of the Medial Pectoral nerve?

Answer 10

Lateral pectoral innervates the Pectoralis major (L for large); whereas the medial pectoral nerve innervates both the pec minor and pec major

Question 11

Describe the general myotome regions of the upper limb.

Answer 11

The myotomes travel in a gradient from more proximal limb corresponding to the lower spinal trunk of the brachial plexus, to the more distal being closer to T1. C5-C6 innervates the shoulder, C6-7 = arm, C7-8 = forearm, C8-T1 = hand

Question 12

What does the dorsal scapular nerve innervate?

Answer 12

(C5) Rhomboids and levator scapulae

Question 13

What does the suprascapular nerve innervate?

Answer 13

(C5-C6) Infraspinatus and Supraspinatus

Question 14

What muscle does the Thoracodorsal nerve innervate? What artery supplies it?

Answer 14

(C5-C7) Latissimus Dorsi also supplied by thoracodorsal artery

Question 15

What does the Long Thoracic nerve innervate? What is the blood supply to this muscle?

Answer 15

(C5-C7) Serratus anterior is also supplied by the lateral thoracic artery from the second region of the axillary artery.

Question 16

What are the spinal roots for each of the terminal branches of the brachial plexus?

Answer 16

Musculocutaneous nerve = C5-C7
Axillary nerve = C5-C6
Radial nerve = C5-C8
Median nerve = C6-T1
Ulnar nerve = C8-T1