If the radial nerve is severed at the origin of the triceps brachii, what motion is not allowed?

Question

If the radial nerve is severed at the origin of the triceps brachii, what motion is not allowed?

a). extension

b). flexion

c). pronation

d). supination

e). rotation

I chose e) but I'm still not entirely sure. I know the triceps facilitate elbow extension but if you lose them the posterior deltoid can help with that motion. Flexion is still allowed since those muscles are not affected by the radial nerve. Pronation is facilitated by the flexors of the hand which again are not associated with the radial nerve. The supinator is on the posterior side of the forearm and innervated by radial nerve. So the only option would be rotation but that for some reason doesn't make any sense.

Answer 1

You are correct in your assessment. If the radial nerve is severed at the origin of the triceps brachii, the motion that is not allowed is:

d) supination

Your reasoning is accurate; the radial nerve innervates the supinator muscle, which plays a crucial role in the supination of the forearm.

Please let me know your thoughts,

Best wishes

Answer 2

The correct answer would be a) extension. The deltoid muscle does not cross the elbow joint, therefore plays no role in elbow movement. The triceps is the only muscle that does elbow extension and is innervated by the radial nerve. Rotation is a movement at the shoulder, therefore is not an option. The other options are motions involving muscles innervated by different nerves.