The flexor carpi ulnaris is a muscle that adducts and flexes the hand at the wrist. The muscle attaches to both the humerus and the base of the 5th metacarpal. Based on the movement that this muscle performs, which attachment is the origin?

• A. Humerus.
• B. Wrist.
• C. 5th metacarpal.
• D. It's impossible to say from the information given.

Answer: (A)

Verified step by step guidance

1. Understand the terms: The 'origin' of a muscle is the attachment site that doesn't move during contraction, while the 'insertion' is the attachment site that moves.
2. Identify the movement: The flexor carpi ulnaris muscle adducts and flexes the hand at the wrist. This means it pulls the hand towards the body and bends the wrist.
3. Consider the attachments: The muscle attaches to the humerus (upper arm bone) and the base of the 5th metacarpal (bone in the hand).
4. Determine which attachment moves: During wrist flexion and adduction, the hand (and thus the 5th metacarpal) moves, while the humerus remains stationary.
5. Conclude the origin: Since the humerus is the attachment that does not move during the muscle's action, it is the origin of the flexor carpi ulnaris.