| A | B |
|---|
| Exoskeleton | A body covering, typically made of chitin, that provides support and protection |
| Invertebrates | Organisms from kingdom Animalia with no backbone |
| Arthropods | Animals with exoskeletons |
| Chitin | A chemical that is both tough and flexible that the exoskeleton is made of. |
| Voluntary muscles | Muscles you can control them by thinking about it. For example, if you want to move your arm to touch something, you think about the motion, and your muscles perform it. |
| Tendon | muscles typically taper as they get near the skeleton, and they end in a tendon, which attaches to the skeleton. |
| Joints | Muscles allow us to move because the skeleton is jointed. |
| Hinge joints | Can be found at the elbow and the knee. They act like the hinges on a door, allowing up and down (or left and right) motion, but that is all. |
| Ball-and-socket joints | These joints ave a ball-shaped head that fits into a bowl-shaped socket. This design allows for a wide range of motion. The ball can roll around in the socket, providing left and right motion along with up and down motion. The hip joints and shoulder joints are good examples of these types of joints. |
| Saddle joint | These joints are more or less in between a hinge joint and a ball-and-socket joint. These joints are composed of two saddle-shaped bones that fit together. The saddles can slide along each other, allowing left to right motion as well as up-and-down motion, but the bones are not as free to move as they are in a ball-and-socket joint. Your ankle joint is a good example of a saddle joint. |
| Washer joint | This joint exists only in your backbone |
| Vertebrae | Your backbone is made up of individual bones called this. Each vertebra (singular of “vertebrae”) is connected to the other with a washer joint made of a cartilage disk. Each joint allows a small range of motion. Together, however, all these types of joints in your backbone allow you to bend and arch your back. |
| Articular cartilage | The bones in a joint are covered with this. This cartilage is tough, but it is also flexible. Similar in feel to hard plastic, it is firm but smooth and resilient. |
| Ligaments | Two bones that are jointed together are held together by strips of tissue called this. |
| Articular capsule | Most joints are surrounded by a “bag” called this. |
