Question

In a case of Erb's palsy, where roots C5 and C6 of the brachial plexus are avulsed (torn out) which muscle is paralyzed?

A. Latissimus dorsi
B. Pectoralis minor
C. Supraspinatus
D. Trapezius
E. Triceps brachii

Answer 1

The supraspinatus muscle is paralyzed in a case of Erb's palsy with avulsed roots C5 and C6, and is responsible for abducting the arm at the shoulder joint. The triceps brachii is the muscle that extends the forearm.

Step-by-step explanation:

In a case of Erb's palsy where the roots C5 and C6 of the brachial plexus are avulsed, the muscle that is paralyzed is the supraspinatus muscle. The supraspinatus muscle is responsible for abducting the arm at the shoulder joint. It is one of the rotator cuff muscles which help stabilize the shoulder. When C5 and C6 roots are damaged, this muscle, along with others innervated by these nerves, can be affected leading to paralysis of the muscle.

To answer another related question, the muscle that extends the forearm is the triceps brachii. It is the primary extensor of the forearm at the elbow joint. The lateral and medial heads of the triceps originate from the humerus, while the long head originates from the scapula, and all three converge on the olecranon process of the ulna.