if the radial nerve is damaged supination is weakened but not eliminated, what muscle reinforces supination?

Question

if the radial nerve is damaged supination is weakened but not eliminated, what muscle reinforces supination?

a). biceps brachii

b). brachialis

c). aconeus

d). coracobrachialis

e). other __________

I think there was another choice for e but I cant remember so I put a blank there

Answer 1

The main muscles that contribute to forearm supination are the aptly named supinator muscle and the biceps brachii. The supinator muscle originates at the lateral epicondyle of the humerus and the supinator crest of the proximal ulna. It inserts onto the lateral, posterior, and anterior portions of the proximal 1/3 of the radius. It functions to supinate the forearm (as the name implies) and is solely innervated by the radial nerve. If the radial nerve is no longer functional, the supinator can no longer contribute to supination.

The biceps brachii has two heads ("bi" in biceps meaning two): the short head which originates from the coracoid and the long head which originates from the supraglenoid tubercle. These heads join and insert onto the biceps tuberosity of the proximal radius. The biceps functions to both flex the elbow AND supinate the forearm (it's actually a stronger supinator than elbow flexor). The biceps brachii is innervated by the musculocutaneous nerve and therefore will take over the job of supination if the radial nerve is damaged.

As a side tip, if you ever forget the difference between forearm supination and pronation, think supination is how you hold a can of soup (palm facing up)!

Answer 2

The muscle that reinforces supination when the radial nerve is damaged is:

a) biceps brachii

Answer 3

The only muscle that supinates the forearm & is innervated by the radial nerve is the supinator muscle. Of the above multiple choices, both biceps brachii and the brachialis cross the elbow joint, and thus contribute to supination. This 2 muscles would be more involved with supination in the case of a radial nerve injury. I'm guessing choice e) would be both an and b, therefore e would be the correct answer. Also note that brachialis only supinates from a pronated position.