BRACHIAL PLEXUS

Q.)  10 Yr old boy is diagnosed with an upper brachial plexus injury . He presents with his right upper arm at his side due to loss of abduction. Which of the following muscles are primarily responsible for abduction of the arm at the shoulder?

A. Deltoid and biceps brachii

B. Deltoid and supraspinatus

C. Deltoid and infraspinatus

D. Supraspinatus and infraspinatus

E. Coracobrachialis and supraspinatus

Ans:  B. The deltoid and supraspinatus muscles, which are innervated by the axillary and suprascapular nerves, respectively, are the primary abductors of the arm at the shoulder

Q.)  Injury to the  musculocutaneous nerve results in which of the following findings?

A. Weakness of abduction of the arm at the shoulder

B. Weakness of adduction of the arm at the shoulder

C. Weakness of extension of the forearm at the elbow

D. Weakness of flexion of the forearm at the elbow

E. Weakness of supination of the forearm and hand

Ans:  D. Injury to the musculocutaneous nerve will result in loss or weakness of flexion at the elbow due to paralysis of the biceps brachii and brachialis muscles.

Q.) A 22-year-old man is brought into the emergency department with a knife injury to the axilla. The physician suspects injury to the lower brachial plexus. Which of the following nerves is most likely to be affected?

A. Axillary

B. Musculocutaneous

C. Vagus

D. Radial

E. Ulnar

.

Ans:  E. The C8 and T1 portions of the lower brachial plexus make up the majority of the ulnar nerve.