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Babies are born with 300 bones in their body; however, because some of the bones fuse together as we grow, an adult has only about 206 bones in the appendicular skeleton.
The human skeleton is called an endoskeleton because it is internal and surrounded by skin and muscles.
Our bones are jointed for flexibility and ease of movement — and they are rigid for structural strength.
There are actually two skeletons, the appendicular and the axial:
The appendicular skeleton is formed by the pectoral girdles (shoulders), the upper limbs, the pelvis, and the lower limbs. They make movement possible and they protect the major organs of digestion, excretion and reproduction.
The axial skeleton has 80 bones. It includes the vertebral column, the rib cage, and the skull. We are able to stand upright because of the axial skeleton, which transmits the weight from the upper body down to the lower body at the hip joints.
Functions of the Skeleton
The skeleton serves six major functions:
Support: The skeleton supports the body, maintains its shape, and provides a framework for the muscles and internal organs.
Movement: The joints — about 360 of them — allow many movements and articulations of our body. 2
Protection: The skeleton helps protect our internal organs from being damaged, although there is clearly a limit to its ability to protect.
Blood cell production: Blood cells are developed in the bone marrow.
Storage of Some Minerals: Bone can store calcium. As well, it is involved in both calcium and iron metabolism.
Endocrine regulation: Bone cells release a hormone which contributes to the regulation of blood sugar and fat deposition.
Without our skeleton, we would be very different creatures — just a blob on the floor without that support and protection.
The skull is not just one bone, but twenty-two. Eight large flat bones, joined by immovable joints, make up the cranium. The many smaller bones of the face hold the eyes in place as well as attach to many muscles that move the head, eyes, and jaw.
The skull protects the brain, fixes the distance between the eyes to allow stereoscopic vision, and fixes the position of the ears to help the brain use auditory cues to judge direction and distance of sounds. In some animals, of course, the skull also has a defensive function: the frontal bone is where horns are mounted.
The spine (or vertebral column) extends from the skull to the pelvis; it supports the weight of the body while also protecting the spinal cord and nerves. It is formed by thirty-three individual vertebrae and is divided into five sections:
- 7 cervical vertebrae (immediately below the skull);
- 12 thoracic vertebrae (the middle segment);
- 5 lumbar vertebrae (the lower back where the spine curves inward);
- 5 sacral vertebrae (at the inferior end of the spine); and,
- 4 coccyx (including the tailbone) vertebrae.
The vertebrae of the sacrum and coccyx fuse in adulthood. The total length of the spinal column in an adult is approximately 70-72 cm.
The Chest and Ribs
The chest is composed of the thoracic vertebrae, ribs and sternum. The ribs and sternum form the chest cavity and protect internal organs, particularly the heart and lungs. In addition, major muscles which assist in breathing attach to the rib cage.
There are twelve pairs of ribs divided into three categories:
- Ribs 1-7 (true ribs) attach directly to the sternum by cartilage;
- Ribs 8-10 (false ribs) join into one common cartilage before attaching to the sternum; and,
- Ribs 11-12 (false or floating ribs) do not attach to the sternum.
The Shoulder Girdle
The shoulder girdle consists of the clavicle (collar bone) and the scapula. It attaches the upper limbs to the axial skeleton and provides attachment sites for several muscles that move the upper limbs.
Another name for the shoulder girdle is the pectoral girdle. There is no other joint between the scapula and the rib cage; however, the muscular connection between the two allows great mobility. The arm is not usually involved in weight bearing, so its stability has been sacrificed for greater mobility.
Bones of the Upper Limbs
Not all creatures have arms; dogs and cats, for instance, do not. But we humans do have arms and they allow us to do many different tasks and movements.
There are thirty bones in the arm and hand.
The upper arm is formed by the humerus and articulates with the scapula and the bones in forearm.
Two bones — the radius and ulna — form the forearm.
The hand is composed of many small bones: the carpals, metacarpals and phalanges. What we can do with our hands allows us to do many things that other creatures cannot do.
A thumb that can be placed opposite the fingers of the same hand is known as an opposable thumb; it allows the digits to grasp and handle objects.
The Pelvic Girdle
The pelvic girdle articulates with the femur and sacrum (one half of the pelvis). Each pelvic bone has three fused components: ilius, ischium, and pubis. The bones of the pelvic girdle are more massive than the upper body bones due to their weight bearing responsibilities.
The pelvic region of the trunk includes several structures:
- the bony pelvis, which is the part of the skeleton embedded in the pelvic region of the trunk; this is subdivided into: (1) two hip bones which connect the spine to the lower limbs, and (2) the pelvic region of the spine (sacrum, and coccyx);
- the pelvic cavity with the pelvic brim above and the pelvic floor below;
- the pelvic floor which is below the pelvic cavity;
- the perineum which is below the pelvic floor.
As mentioned above, the pelvic girdle supports the entire upper body. It is little wonder that the hip joint sometimes has problems after years of supporting us.
Bones of the Lower Limbs
The bones of the lower limbs carry the entire weight of the body and include the femur (thigh), tibia and fibula (lower leg), and the bones of the ankle and foot.
The longest and strongest bone in your body, the femur (thighbone), is about 1/4 of your height.
The foot includes seven tarsal bones, five metatarsals, and fourteen phalanges. The most prominent are the talus or ankle bone that articulates with the tibia and the calcaneous to form the heel bone. Together the talus and calcaneous transmit most of the weight of the body to the ground. The metatarsal bones form the sole of the foot while the phalanges form the toes.
The bones of the foot form three arches that give the foot strength and flexibility. The arches assist in distributing the weight to the heel and toes of the foot.
When we are actively participating in running and jumping, the lower limbs are subject to very high forces. Consequently, the lower limb bones are the strongest and biggest in the body.
Joints exist whenever two or more bones of the body meet. Although structurally the weakest part of the skeleton, joints allow us much greater movement in a variety of ways.
Consider the many joints we have: shoulders, neck, knees, hips, wrists, elbows, ankles, as well as small joints in both toes and fingers.
As we age, it is often at the joints that we have the most changes — usually osteoarthritis develops, and if there have been injuries in our youth, they can bother us more in older age. Modern-day medicine has developed ways to replace joints — most particularly the knees and hips, but shoulders are sometimes being done now too.
For more detail about joints, see the list at the end of this article for articles about the various joints.
The Content of Bones
Bone contains specialized cells and a cement-like material known as matrix which is made of protein and calcium. Bone must be both flexible and strong so that it can move, bear weight, and produce force. Collagen supplies the flexibility while the matrix provides strength and hardness.
Approximately 99% of the calcium in the body is found in bone tissue. It is essential to bone health and overall body function.
With too little calcium in the blood, the nervous system becomes overly excited which can lead to muscle tremors, spasms and tetanus (inability to relax).
On the other hand, excessive calcium in the blood can lead to depression of the nervous system, muscle weakness, delayed reflexes and even a heart attack.
Maintaining an acceptable calcium level in the blood depends on:
- dietary intake of calcium;
- kidney function; and,
- bone tissue release or storage of calcium.
As well, hormones regulate the balance between storing and/or releasing calcium.
Although bone may appear to be solid and unchanging, it is actually a living, dynamic part of your body. This is why it’s important to eat a well balanced diet, which includes foods rich in calcium, and also add weight bearing exercises in your workouts to build and maintain bone density.
For a more detailed discussion of some of these topics, check out these articles:
- Exercise and Osteoporosis
- Back Problems
- Bones of the Hands and Feet
- The Hip Joint
- Hip Replacement
- Joints and Exercise
- The Knee Joint
- Knee Replacement: The Basics
- The Ribs
- The Shoulder Joint
- The Spine
- Three Arm Bones: the humerus, the radius, and the ulna
- Three Leg Bones: The femur, the tibia, and the fibula
- The Wrist and the Ankle
Thanks to Wikipedia for much of the information and most of the graphics for this article.
I am a BCRPA-certified fitness instructor in Vancouver, BC. I teach four classes at the West End Community Centre in Vancouver, BC, mostly designed for the older adult. The Inevitable Disclaimer: Everything published here expresses only my opinion, based on my training and research. What you do with the information is entirely your own responsibility. I am not liable for any injury you suffer that seems to be related to anything you read here. Always consult your doctor before beginning an exercise program. For other articles, return to the table of contents.
These three dots behave exactly like a footnote. Click on them and you will get more information about the topic. ↩
Consider how many joints we have: fingers and toes, elbows, shoulders, wrists, ankles, knees, hips, neck. Then think about the things we could not do if any particular joint was not working. ↩