Here's why:
* Muscular system: Muscles provide the force needed for movement. When a muscle contracts, it pulls on a bone, causing it to move. In the case of bending the arm, muscles like the biceps brachii contract, pulling on the radius bone and causing the arm to bend at the elbow joint.
* Skeletal system: The bones provide the framework and structure for the body. The elbow joint, formed by the humerus, radius, and ulna bones, allows for the bending and straightening of the arm. The bones act as levers, allowing the muscles to exert force and create movement.
While other systems like the nervous system (sending signals to the muscles) and circulatory system (supplying oxygen and nutrients to the muscles) are essential, the muscular and skeletal systems are the direct actors in arm bending.
