Help defend free speech and free scientific inquiry in the U.S. Sign the Academic Freedom Petition.

Skeletal system

From CreationWiki, the encyclopedia of creation science

(Redirected from Skeleton)

Human skeleton showing the axial (blue highlight) and appendicular bones.

The skeletal system is a support and protection structure for animals. There are two main types of skeletal systems. The endoskeleton is an interal support system of the type possessed by humans and other vertebrates, which is made of bone. The exoskeleton is an external system that was designed for many invertebrates such as the crustaceans and insects. The composition of exoskeletons vary widely, but known constituents include calcium salts, protein, carbohydrates (chitin) and silicate.

Main Functions:

It provides support for the overall body.
It offers a place for muscle and tendons to attach.
It provides a great amount of protection for the vital organs inside of the creature.
It adds leverage for increased range of motion.
Bones continuously produce blood cells and store calcium.

1 Endoskeleton
2 Exoskeleton
3 Related References
4 Gallery
5 See Also

Endoskeleton

In vertebrates, the endoskeleton is sturdy internal frame that is centered on a prominent spine (vertebral column). Most skeletal systems consists of bones, cartilage, ligaments and tendons and accounts for a significant portion of the body weight (about 20 percent in humans). The living bones use oxygen and give off waste products in metabolism. They contain active tissues that consume nutrients, require a blood supply and change shape or remodel in response to variations in mechanical stress.[1]

Main Groups

Bones can be grouped in two divisions: axial skeleton and appendicular skeleton. The axial skeleton forms the vertical axis of the body. They include the bones of the head, vertebral column, ribs and breastbone or sternum. The appendicular skeleton includes the free appendages and their attachments to the axial skeleton. The free appendages are the upper and lower extremities, or limbs, and their attachments which are called girdles.[2]

Bone Types

Diagram of the spongy and compact layers of the bone

There are three different types of bone in the skeletal system. These are the outer layer of the bone, the compact middle layer, and the spongy third layer.

Periosteum

The periosteum is hard and smooth. It provides protection to the rest of the layers of the bone. It is almost like the "skin" of the bones. The periosteum provides a site for the attachment of muscles, and also contains nerves, blood vessels, and lymphatic vessels.[3]

Compact

The compact bone is extremely dense and surrounds the spongy bone. The compact bone also contains many Haversian canals, which also contain nerves and blood vessels. This layer of bone gives the skeleton its strength and allows it to support your bodies mass.[4]

Spongy

The spongy bone is where all of the blood cells are created from the bone marrow. Spongy bone contains two different types of bone marrow: red and yellow marrow. The red bone marrow produces red and white blood cells and platelets. The yellow bone marrow, however, is used to store fats.[5]

Joints

There are four different primary joints located throughout the body. These are the hinge, the ball and socket, the picot, and the glide joints. The each serve different purposes, and are located in areas best suited for those purposes.

Hinge

The hinge joint is basically a hinge. It can move up and down or from side to side, but within a 180^o range. A very common example of this is a person's elbow or knee. Hinge joints usually have a lot of stress placed on them, and the knee is a very common example of this. Knee surgery is more common than any other surgery performed on a joint, because they are used rigorously each day. They are the joints that move you up, down, forward, and they have to carry all of your weight. This stresses the knee joint so much that it is not uncommon for even an average person to damage them in some way.

Ball and Socket

The shoulder is an example of a ball and socket joint

The ball and socket joint allows for increased range of movement. The best examples of this type of joint are the shoulder and hip joints. Even though the shoulder is considered a ball and socket joint, the hip is considered the most "true" ball and socket joint because the ball is almost completely enclosed by the socket. The shoulder is more like a ball resting inside of a shallow dip, rather than being fully encompassed. This does, however, offer increased mobility and range, at the cost of being easier to pop out of joint or being injured. Shoulder problems are very common because of this joint structure. In fact, 13.7 people in the United States had treatment for shoulder-related problems in 2003.[6]

Pivot

Human vertebral column

The pivot joint allows for the most movement out of all of the joints. The most common example of this joint is the neck, which can look from side to side, up and down, and almost any way at all. This joint is used primarily to be able to see your surroundings without turning your whole body. This helps when you are driving or carrying large objects, but other than that, there is little else that it can do.

Glide

The glide joint is similar to the ball and socket joint in terms of the range of movement, but there is no actual ball and socket. An excellent example of this is a person's wrist, which has extreme mobility but no bulky ball and socket like the shoulder. Glide joints are also very delicate, and can be easily damaged. They are also very weak, and cannot apply very much force by themselves. For example, try lifting a 30 lb weight with your whole arm, and then try lifting the same weight using just your wrist. Gliding joints are useful, but lack a lot of support that allows other joints to apply more force.

Broken Bones

Your bones are tough stuff - but even tough stuff can break. Like a wooden pencil, bones will bend under strain. Most fractures occur in the upper extremities: the wrist, the forearm, and above the elbow. Also if the pressure is too much, or too sudden, bones can snap. You can break a bone by falling off a skateboard or crashing down from the monkey bars.

Bones can fracture in a number of different ways. A fracture may be a straight break across the bone (transverse fracture), slanting (oblique fracture) or winding (spiral fracture). The break may run along the shaft of the bone (longitudinal fracture), or the bone may be shattered into pieces (comminuted fracture). Young bone is softer and more able to bend than adult bone, so childrens bones often fracture on one side but bend on the other - known as a greenstick fracture.[7]

There are many different types of fracture, the most common of which is a simple fracture, when a bone breaks cleanly. If you put out your arms when you fall, you could end up with an impacted fracture, where the ends of two bones are forced into one another. A sharp sudden twist of a bone in a game of football could result in a jagged spiral fracture. Road accidents often cause comminuted fractures, where a bone breaks into fragments, or compression fractures, where a bone is crushed.[8]