Axilla, Brachial Plexus

Question 1

What is the medial boundary of the axilla?

Answer 1

Serratus anterior.

Question 2

What is the posterior boundary of the axilla?

Answer 2

Subscapular muscles.

Question 3

What is the anterior boundary of the axilla?

Answer 3

Pectoral muscles.

Question 4

What forms the apex of the axilla?

Answer 4

The junction between clavicle, scapula, and first rib.

Question 5

What are the three main contents of the axilla?

Answer 5

Axillary vessels
Axillary lymphatics
Brachial plexus

Question 6

Name the five groups of axillary lymph nodes.

Answer 6

Lateral
Subscapular
Pectoral
Central
Apical

Question 7

What is the subclavian line?

Answer 7

It refers to the pathway and location where subclavian vessels and brachial plexus structures travel through the apex of the axilla (important for central line access or thoracic outlet syndrome).

Question 8

What does the brachial plexus supply?

Answer 8

Motor and sensory innervation to the upper limb.

Question 9

What does the radial nerve supply?

Answer 9

Dorsal compartments (extensors of upper limb).

Question 10

What does the musculocutaneous nerve supply?

Answer 10

Flexors of the upper arm (ventral compartment).

Question 11

What does the median nerve supply?

Answer 11

Flexors of forearm and hand – radial side (ventral compartment).

Question 12

What does the ulnar nerve supply?

Answer 12

Flexors of forearm and hand – ulnar side (ventral compartment).

Question 13

What nerves contribute to the cutaneous sensation of the hand?

Answer 13

• Median nerve: Lateral palm, thumb, index, middle, and half of ring finger
• Ulnar nerve: Medial palm, little finger, and half of ring finger
• Radial nerve: Dorsum of hand (thumb to half of ring finger – NOT fingertips)

Question 14

What does a specific brachial plexus lesion result in?

Answer 14

Predictable patterns of motor and sensory loss depending on affected nerve(s).

Question 15

What are dermatomes?

Answer 15

Skin areas supplied by sensory fibers of a single spinal nerve.

Question 16

What dermatome corresponds to the thumb?

Answer 16

C6.

Question 17

What dermatome corresponds to the middle finger?

Answer 17

C7.

Question 18

What dermatome corresponds to the little finger and medial forearm?

Answer 18

C8 and T1.

Question 19

What are myotomes?

Answer 19

Muscle groups innervated by motor fibers from a single spinal nerve.

Question 20

What is the myotome for shoulder abduction?

Answer 20

C5.

Question 21

What is the myotome for elbow flexion?

Answer 21

C5–C6.

Question 22

What is the myotome for elbow extension?

Answer 22

C7.

Question 23

What is the myotome for finger flexion and extension?

Answer 23

C8 (flexion), C7 (extension).

Question 24

What is the myotome for finger abduction/adduction?

Answer 24

T1.

Question 25

What causes Erb’s palsy?

Answer 25

Upper brachial plexus injury (C5–C6).

Question 26

What are the symptoms of Erb’s palsy?

Answer 26

Arm hangs by the side (adducted) Medially rotated shoulder Extended elbow "Waiter's tip" position

Question 27

Which myotomes and dermatomes are affected in Erb’s palsy?

Answer 27

C5–C6.

Question 28

What causes Klumpke’s paresis?

Answer 28

Lower brachial plexus injury (C8–T1).

Question 29

What are the symptoms of Klumpke’s paresis? 3

Answer 29

Weakness of intrinsic hand muscles Claw hand Possible Horner's syndrome (if T1 sympathetic fibers involved)

Question 30

How do you test T1?

Answer 30

- Sensation over medial side of the forearm - Finger adduction/abduction (small hand muscles)

Question 31

What is the key sensory deficit in radial nerve injury?

Answer 31

Loss of sensation over the dorsal web space between thumb and index finger.

Question 32

What is the key motor deficit in radial nerve injury?

Answer 32

Weakness of wrist and finger extensors.

Question 33

What classic clinical sign is seen in radial nerve injury?

Answer 33

Wrist drop – inability to extend the wrist and fingers.

Question 34

What sensory areas are affected in ulnar nerve injury?

Answer 34

Medial aspect of palm, little finger, and medial half of the ring finger.

Question 35

What motor deficit leads to the 'ulnar claw'?

Answer 35

Inability to extend the 4th and 5th digits due to interossei and lumbrical weakness.

Question 36

What is the 'ulnar paradox'?

Answer 36

The closer the nerve lesion is to the hand, the worse the claw appears — because proximal lesions paralyze more muscles that counteract the claw.

Question 37

What sensory loss occurs in median nerve injury?

Answer 37

Palmar surface from the thumb to the lateral half of the ring finger.

Question 38

What is the motor deficit when attempting to make a fist in median nerve injury?

Answer 38

Inability to flex 2nd and 3rd digits – resulting in the ‘Hand of Benediction’.