Biological Systems MCAT Practice Exam

What type of joint is characterized by being immovable, with two bones fused together?

1. Diarthroses

2. Amphiarthroses

3. Synarthroses

4. Synovial joints

The correct answer is: Synarthroses

The type of joint that is characterized by being immovable and involves two bones fused together is known as synarthroses. This type of joint is designed to provide strength and stability, often seen in areas where protection is needed. A classic example of synarthroses is the sutures of the skull, where the bones of the skull are tightly bound together, providing both structural integrity and protection for the brain. In contrast, other categories of joints have different characteristics. Diarthroses, for instance, are freely movable joints, such as the knee and elbow, which allow a wide range of motion. Amphiarthroses refer to joints that allow for slight movement, such as those found in the spine, providing more flexibility than synarthroses without the full range of movement seen in diarthroses. Synovial joints, while also categorized under diarthroses, specifically involve a joint cavity filled with synovial fluid, further facilitating movement. All these distinctions highlight why synarthroses uniquely represent immovable joints where bone fusion occurs, reinforcing its classification as the correct answer.