In vertebrate anatomy, the axial skeleton includes the skull, rib cage, and vertebral column. These structures comprise the head and trunk of the organism, the most vital parts of the body. The rest of the skeleton, the extremities and their points of attachment, is known as the appendicular skeleton. Together, these two skeletal systems make up an organism's complete skeleton, providing structure and support the organism and interacting with systems such as the muscles to allow an organism to move.
The structures of the axial skeleton are critical to an organism's function. The 28 bones of the skull provide a layer of protection for the brain, and also create housing for the ears, eyes, nose, and mouth, so that the organism can interact with the surrounding environment. These bones also change over time, starting out separated so that the head can grow to accommodate the brain, and slowly fusing together over time to provide more protection as the organism matures. Connecting to the skull, the vertebral column carries messages down the body, with a number of connecting nerves networking the extremities with the vertebral column and the brain.
The rib cage, which includes the ribs, sternum, and vertebral points of attachment, acts to protect the internal organs, while also flexing and moving with the body so that an organism can breathe, eat, and engage in other activities. Damage to any component of the axial skeleton can be dangerous for an organism, as it exposes vital organs to damage, and it can also cause severe pain.
Structures in the appendicular skeleton are also important, as they allow the organism to navigate the natural environment, but they are not as critical as those in the axial skeleton. Living without an arm or leg, for example, is possible, while someone missing part of the skull or ribcage would face serious obstacles. Malformations in the axial skeleton can also be a cause for concern, as they may interfere with an organism's develop as it matures.
Samples of the axial skeleton are sometimes prepared for study by medical students and those interested in biology. These samples are easier to manage than an entire skeleton, and they reveal important information about the critical structures of the skeleton. Medical students also usually explore the axial skeleton and the connected muscular and nervous systems during the phase of their educations in which they perform dissections and other anatomical explorations to learn more about the body.