The skeletal system works in conjunction with the muscular system to help a person move. Without the skeleton, humans and other animals would simply be a blob of tissue without any protection.
Humans have endoskeletons, which are skeletal systems that are located inside their bodies. The skeleton offers protection to the internal organs and the brain while helping the body keep its muscles, fat and skin upright. Muscles connect to the skeleton and contract and relax as the body moves.
The skeletal system is made of calcified bone and cartilage, and in the bone, red and white blood cells are made. The hard, calcified bones in the system also work with the circulatory system.
Unlike humans and other mammals, some animals such as crustaceans and insects have an exoskeleton, which is a skeleton outside the body. These skeletons are not made of bone, but rather hard calcified plates.
Besides bones and cartilage, the skeletal system consists of tendons and ligaments. Although teeth are considered to be part of the skeletal system, they are not bones. Teeth are made of dentin and enamel. Different bones that make up the skeletal system have different names. For example, the skull is called the cranium and the bones that protect the spinal cord are called vertebrae.