The Skeletal System Study Guide

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Updated on Sep 22, 2011


The skeletal systems of organisms work with the muscles to allow the movement of body parts and the locomotion of the whole organism. They also protect the soft internal organs from injury. The skeletal system also acts as a repository of minerals used in various aspects of metabolism. In vertebrates, the interiors of bones in the skeletal system are responsible for producing blood cells. Skeletal systems appear in arthropods (insects and crustaceans) and vertebrates (birds, fish, reptiles, and mammals). In arthropods, the skeletal system is an exoskeleton, and in vertebrates, the skeletal system is an endoskeleton.

Vertebrates and Invertebrates

Earlier, when classifying animals, it was mentioned that we separate multicelled animals into two overall, large groups. Those two groups are the vertebrates (those animals with backbones) and the invertebrates (those without backbones).Many invertebrates have no internal skeleton, but they have what is called an exoskeleton, which is a hard outer coating. Insects, crabs, and lobsters all have exoskeletons. Muscles can attach to the exoskeleton, which acts as protective body armor. The disadvantage to an exoskeleton is that it limits the organism's growth. Many invertebrates have worked around this problem by molting (or shedding) their exoskeletons at various stages in their life cycles so that they can grow their bodies and then grow a new exoskeleton.

In vertebrate animals, the skeleton is internal (an endoskeleton) and has evolved structures called vertebrae, which are hard, bony projections surrounding the spinal cord. This vertebral column is commonly known as the backbone. Although the exoskeleton of invertebrates is dead, excreted tissue (such as hair and nails), the endoskeleton of vertebrates is composed of living tissue that is known as the skeletal system. The cells that make up the skeletal system are called osteocytes, and they associate together to form connective tissue. This connective tissue, along with cartilage tissue (another type of connective tissue), comprises the skeletal system. Because the skeletal system is alive, it can grow with the organism and molting is not necessary.

The Skeletal System

The skeleton is the chief structural system, which, along with the skin, provides form and shape to the body. In human beings, the skeletal system has 206 bones, most of which are in the hands and feet. The bones of the skeletal system are rigid, but the whole system is flexible because of the joints where bones are joined.

This system of bones is highly coordinated with the muscular system. The nervous system is responsible for the coordination necessary for such actions as painting fine detail in a picture or participating in an Olympic decathlon. The skeletal system is a wonderful example of how specialized tissues, collected together into several different organ systems, are further organized into cooperative groups of interacting systems. The muscular and skeletal systems are so closely linked that they are often referred to as one large system called the musculoskeletal system.

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