[007] Axilla and brachial plexus

Question 1

what does long thoracic nerve innervate?

Answer 1

serratus anterior

Question 2

what may damage to long thoracic nerve cause?

Answer 2

“winging” of scapula

Because the long thoracic nerve passes down the lateral thoracic wall on the external surface of the serratus anterior muscle, just deep to skin and subcutaneous fascia, it is vulnerable to damage. Loss of function of this muscle causes the medial border, and particularly the inferior angle, of the scapula to elevate away from the thoracic wall, resulting in characteristic “winging” of the scapula, on pushing forward with the arm. Furthermore, normal elevation at the arm is no longer possible.

Question 3

where does the brachial plexus arise from

Answer 3

ventral rami of C5-T1

Question 4

what are the “levels” of brachial plexus
hint: starting from roots

Answer 4

5 roots (C5, C6, C7, C8, T1)
3 trunks ( superior, medial, inferior)
6 divisions ( into anterior and posterior)
3 cords ( lateral, posterior, medial)
4 terminal nerves (musculocutaneous nerve, median nerve, radial nerve, ulnar nerve)

Question 5

what form of innervation do branches of roots and trunks provide?
hint: is it motor, sensory, both or one only

Answer 5

motor innervation only

Question 6

how many branches are there from roots

Answer 6

3

Question 7

what are the branches from roots (ventral rami)
and what do they innervate

Answer 7

dorsal scapular nerve (C5)
- rhomboid major and minor muscles, part of levator scapulae w C3-C4

long thoracic nerve (C5-C7)
- serratus anterior

contribution to phrenic nerve (C5)

Question 8

what are the branches from trunks

Answer 8

branches only come off from superior trunk

1. suprascapular nerve
   - supraspinatus, infraspinatus muscle
2. nerve to subclavius

Question 9

how are the cords named

Answer 9

lateral, medial, posterior
relative to 2nd part of axillary artery

Question 10

what is the branch from lateral cord

Answer 10

lateral pectoral nerve (C5-C7)
- pectoralis major

Question 11

what are the branches from medial cord

Answer 11

C8-T1
1. medial pectoral nerve
- pectoralis major and minor

2. medial brachial cutaneous nerve
   - also contribution from T2
3. medial antebrachial cutaneous nerve

Question 12

what are the branches of posterior cord

Answer 12

1. axillary nerve (C5-C6)
   - deltoid, teres minor
   - skin over upper lateral part of arm
2. superior subscapular nerve (C5-C6)
   - subscapularis
3. thoracodorsal nerve (C6-C8)
   - latissimus dorsi
4. inferior subscapular nerve (C5-C6)
   - subscapularis
   - teres major

Question 13

what are the terminal nerves of the brachial plexus from the anterior divisions

Answer 13

1. musculocutaneous nerve (C5-C7)
   - motor to all muscles in the anterior compartment of the arm, sensor
2. median nerve (C5, C6-T1)
   - motor to most muscles in the anterior copartment of forearm, thenar muscles and two lumbricals, sensory
3. ulnar nerve (C7, C8-T1)
   - motor to most intrinsic mucles of the hand and some muscles in the anterior compartment of forearm, sensory

Question 14

what are the terminal branches of brachial plexus from posterior divisions

Answer 14

radial nerve (C5-T1)
- motor to all muscles o posterior compartment of arm and forearm, sensory

Question 15

what are the terminal branches of brachial plexus from posterior divisions

Answer 15

radial nerve (C5-T1)
- motor to all muscles o posterior compartment of arm and forearm, sensory

Question 16

what does pinching the index finger test for?

Answer 16

median (peripheral nerve)
and C7 spinal nerve level ( dermatome)

Question 17

for C5-T1 spinal cord levels, name their respective areas of minimal overlap

Answer 17

C5: upper lateral arm
C6: pad of thumb (I)
C7: pad of index finger (II)
C8: pad of little finger (V)
T1: medial elbow

Question 18

what is Erb’s Palsy (Erb-Duchenne Palsy)

Answer 18

• Damage to roots C5 and C6
• traumatic lateral neck bending
• involves suprascapular, axillary, dorsal scapular, musculocutaneous, radial (some)
• supraspinatus and infraspinatus, deltoid, teres minor, biceps, brachialis
• adducted and medially rotated arm, extended elbow, pronated forearm, “waiter’s tip” position of fingers

Question 19

Klumpke’s Palsy

Answer 19

damage to root of C8 and T1
- traumatic hyperabduction of arm
- paralyses most intrinsic hand muscles
- claw hand presentation, no 4th and 5th interphalangeal extension

Question 20

radial nerve injury

Answer 20

damage to posterior cord or radial nerve
- fracture of humerus, Saturday night palsy, improper use of crutches
- loss of extensors (triceps, brachioradialis, supinator and etensors of wrist and fingers) – wrist drop
- loss of sensation on posterior forearm, elbow and dorsum of hand

Question 21

injury to median nerve

Answer 21

damage to median nerve
- loss of finger and wrist flexors, thenar muscles and 1st and 2nd lumbricals
- cannot flex distal interphalangeal joints on digits 2 and 3 –> benediction hand or Pope’s blessing when attempting to make a fist

Question 22

when you have a dislocation of the glenohumeral joint, which nerve are you most worried about?

Answer 22

axillary nerve