Imagine that you are designing a two-segment robot arm that has the sole function of bending and straightening at a single joint. When designing the robot joint, which joint in the human body would you try to copy? What features would your robot joint share with the biological joint? Would mobility or stability be your priority?

1. Hinge Joint

2. presence of a joint cavity

3. This gives the bones of a synovial joint the ability to move smoothly against each other, allowing for increased joint mobility.

Explanation:

1. This type of joint allows only for bending and straightening motions along a single axis, and thus hinge joints are functionally classified as uniaxial joints. A good example is the elbow joint, with the articulation between the trochlea of the humerus and the trochlear notch of the ulna.

2-3. A key structural characteristic for a synovial joint that is not seen at fibrous or cartilaginous joints is the presence of a joint cavity. This fluid-filled space is the site at which the articulating surfaces of the bones contact each other. At synovial joints, the articular surfaces of bones are covered with smooth articular cartilage. This gives the bones of a synovial joint the ability to move smoothly against each other, allowing for increased joint mobility.