Skeleton

A skeleton is the structural frame that supports the body of most animals. It helps animals stand, move, and protect their internal parts. There are different kinds of skeletons. One type is the exoskeleton, a hard shell on the outside of the body, like the shell of a crab or a beetle. Another type is the endoskeleton, which is inside the body and made of bones or cartilage, like the bones in your own body. Some animals, like jellyfish, have a hydroskeleton, a flexible support system that relies on the pressure of body fluids.

Vertebrates, such as humans, fish, birds, and mammals, have an endoskeleton that includes a central vertebral column. This column, made mostly of bones and some cartilages, helps support and protect the body. Invertebrates, animals without a backbone, have many different kinds of skeletons. For example, insects and crabs have hard exoskeletons, while some sea creatures have internal shells or rods that support their bodies. Even sponges have tiny rods called spicules that help give them shape.

Etymology

The word "skeleton" comes from an Ancient Greek word, skeletós, which means "dried up." An older form of the word is "sceleton."

Classification

Skeletons are the structural frames that support the bodies of most animals. There are three main types: exoskeletons, endoskeletons, and hydrostatic skeletons. Exoskeletons are hard outer shells that protect animals like insects and shellfish. They must be shed when the animal grows larger. Endoskeletons are internal frames made of bone or cartilage, found in animals like humans and fish. These skeletons help support the body and give muscles something to attach to. Hydrostatic skeletons are flexible structures supported by fluid pressure, used by animals like jellyfish and earthworms to help them move and keep their shape.

Vertebrate skeletons

Vertebrate skeletons are internal frames made mostly of bone, with some parts made of cartilage. Bones give shape to the body, help it move, and protect important organs. They are made of minerals and special tissues, and they even help make blood cells.

Birds have special lightweight bones to help them fly, while fish may have bones or just cartilage. In humans, the skeleton supports the body, protects organs, and helps us move. It includes big bones like the femur in the leg and tiny bones in the ear. The human skeleton has around 206 bones when fully grown, but this number can vary.

Invertebrate skeletons

Invertebrates do not have backbones or bone skeletons. Animals like arthropods, including insects, crustaceans, and arachnids, have exoskeletons made of a material called chitin. These exoskeletons protect and support their bodies and are shed when they grow larger.

Other invertebrates, such as echinoderms like starfish and sea urchins, have internal skeletons made of special plates. Some molluscs, like snails and clams, have shells that act as external skeletons. Sponges have tiny, microscopic structures called spicules that make up their skeletons.

Cartilage

Main article: Cartilage

Cartilage is a special type of connective tissue that helps support the body. It is made of cells called chondrocytes and a substance that includes collagen fibers, proteoglycans, and water. There are different kinds of cartilage, such as elastic cartilage, hyaline cartilage, and fibrocartilage. Unlike other tissues, cartilage does not have blood vessels, so it heals and grows more slowly.