An exoskeleton is a braced framework that protects an organism from the outside. An endoskeleton is an internal braced framework. Vertebrate endoskeletons provide support, a lever system, protection, blood cell production, and mineral storage. The properties and organization of the musculoskeletal system vary to accommodate the environment of the animal. The primary components of the skeletal system are cartilage and bone.
Cartilage provides a mold for bone development.
It also forms pads and surface coverings between bones. Coordinated movements result from specific combinations of contracted and relaxed muscle cells. The major muscle cell types are smooth, cardiac, and skeletal. Invertebrates use complex combinations of smooth and striated muscle. Fly wings can beat a thousand times a second.