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Human skeleton

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

The Human Skeleton is a skeletal system composed of a strong framework of bones that supports the human body, protects internal structures, and allows for movement by providing points of attachment for muscles. It also serves lesser known functions, such as a storing important ions, forming new blood cells, and it was recently discovered that bone cells release in important hormone that helps regulate blood sugar and fat deposition.

The human skeletal system is an endoskeleton (internal) that uniquely designed for upright stance and bipedal movement. It consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage.

Contents

Development

Early on in the mother's womb the fetus has a cartilaginous skeleton. The cartilaginous skeleton provides the bases for the long bones to form. This process happens through out gestation and continues into the years after birth. When a baby is born it has 270 bones, but as it grows some of the small bones fuse together. So as an adult a person will have 206 bones, this can vary from person to person.[1]

Organization

Axial skeleton

The skeletal system is divided into two sections; the axial skeleton and the appendicular skeleton. The division of these bones goes along the longitudinal axis, the axial skeleton, is were the appendicular skeleton is attached.[1] The longitudinal axis is an imaginary line running down the center of the body, that is perpendicular to the transverse plane around which rotations in the transverse plane occur.[1]

Axial skeleton

Main Article: Axial skeleton

The axial skeleton contains 80 bones. These bones are found in the head and trunk of a persons body. The bones are divided into five parts the skull, the ossicals(in the inner ear), the hyoid bone (in the throat), the chest (ribs and sternum), and the vertebral column.[2]

The axial skeleton is responsible for the up-right position of the body. The axial skeleton transfers the weight of the head, the chest and the upper extremities down to the lower extremities at the hip joint. Most of the weight is in the spinal column. Which is why we have the erector spinae muscles and a large amount of ligaments attached to it. This is also what causes the "S" shape of the human spine. The 240 muscles of the erector spinae allow small movements in the thoracic cage(chest) for breathing and simple and complex facial movements.[1]

Vertebral column

Main Article: Vertebral column

The human backbone has a natural curve in the lumbar region of the lower back, called Lordosis, while gorillas have a backwards curve so that they are said to have a kyphotic spine. The British researcher Richard Porter noted that this arch is just right to strengthen the spine in the human upright position, and allows humans to lift much more weight than if it were reversed.[3] Some evolution oriented physicians theorized that the arch was a left over from times when ancestors of humans walked on all fours, and tried to "correct" the curve of the spine with exercise. This worked very poorly and was abandoned as being unhelpful for the patients. It was found that exercises that restored the lordosis was most helpful in eliminating back pain.[4]

Rib cage

Ribs are very important to us because they protect important organs like the heart and lungs, as well as provide anchors for important muscles.

Both men and women have twelve pairs of ribs. Someone once said that since God made Eve from Adam's rib, then Adam should have one rib less. This argument doesn't make sense since if a father loses a finger, his sons will still be born with all ten fingers. There is no reason that men should have any less ribs than were originally genetically programmed for men. The article on erroneous arguments speaks to this point, and we should never use as an argument in favor of creation that men have one less rib than women, because it isn't true.

What is interesting is that the human rib has the property of regrowing itself in certain circumstances. In the regenerating ribs] article we can see that ribs can often grow back completely if the bone is carefully removed leaving its surrounding membrane intact. Thus ribs are often used to supply bones for bone grafts in other parts of the body because it keeps growing back. Thus, Adam did not even need to walk around without a rib.[5]

Appendicular skeleton

Appendicular skeleton

Main Article: Appendicular skeleton

The appendicular skeleton contains 126 bones. This part of the skeleton helps with motion, protecting the digesting organs, excretion, and reproduction. The appendicular skeleton is divided into six major parts, they are the pectoral girdle, the arm, the hand, the pelvic girdle, the leg, and the foot.[6] There are 300 muscles attached to the appendicular skeleton. Together with the axial skeleton they make up the human skeleton.[1]

Foot

Our feet have an automatic transmission built in as part of their design. During running, the bones in our feet automatically engage during the moment the foot strikes the ground. This way the bones in our feet make lever arms which are the kept to a low gear ratio when the foot strikes, and shifts automatically to a higher gear ratio as your weight moves over the toe. This allows the calf muscle to work at a lower velocity and thus provide more power to move the body forward. It is difficult to imagine how such a precise mechanism just appeared over time.[7].

Function

Support

The skeleton is the frame work of the human body and helps it maintain its shape. All the muscles and tissues are able to attach to the skeleton as a base.[2]

Protection

The skeleton protects all the vital organs in the body.

  • The eyes, brain, middle, and inner ear are protected by the skull.
  • The lungs, heart, and major blood vessels are protected by the rib cage, sternum, and spine.
  • The shoulder is protected by the clavicle and the scapula.
  • The digestive system, the excretory system, reproductive system, and the hip are protects the ilium and the spine.
  • The knee and elbow are protected by the patella and the ulna.
  • The wrist and ankles are protected by the carpals and tarsals.[1]

Movement

The skeleton is permitted to move by the joints between the bones. Some permit a wide range of movement others are more restricted. The movement is allowed by skeletal muscles that attach to the bone in various places. Muscles, joints, and bones are what allow the skeletal system to move.[1]

There are six types of joints that help the skeleton move: The ball and socket joint allows the joint to move in all direction. It gives the widest range of motion. Examples of the ball and socket are the hip and the shoulder. The condyloid joint allows the joint to move in angular movements but not rotation. Examples of this joint are between the bones of the palm and the hand and between the bones of the foot and the toes. There is only one saddle joint in the body and it's in the thumb. It also allows for a wide rang of motion. The pivot joint allows rotation. An example would be the axis and and the atlas of the neck. The hinge joint allows the joint to only flexion and extension. This occurs in the elbow joint. The gliding joint allows the joint to slide or twist without any circular movement. This happens in the carpals in the wrist and the tarsals in the ankle. [3]

Storage

The bones in the skeletal system can store minerals like calcium and phosphorus. When the supply of these minerals runs low the body will get it from the bones. [4]

Blood Cell Production

The red bone marrow, found in the skeleton, is were haematopoiesis happens. Haematopoiesis is the making of blood cellular components.[1]

Endocrine Regulation

The bone cells release osteocalcin, a hormone that helps regulate blood sugar and fat deposition.[1]

Diseases and Disorders

There are several different disorders and diseases that can effect the skeletal system. The more common ones are fractures, arthritis, tendonitis, poliomyelitis, and scoliosis.

Fractures

There are many types of fractures that can affect the human skeleton in different ways. A transverse fracture is were the bone has broken at a right angle. A greenstick fracture is were the bone is bent. This kind of fracture is an incomplete fracture. An oblique fracture is when the bone breaks at a slope down the bone. A comminuted fracture is when the bone has shattered into several pieces. An impacted fracture is when the bones ends have been driven into each other by force. [5]

Arthritis

Main Article: Arthritis

Arthritis is pain, stiffness, and swelling of the joints. There are over 100 joint diseases that are referred to as arthritis. [6]

Tendinitis

Tendinitis, often called rheumatism, is pain or stiffness of the muscles and joints in the body. [7]

Poliomyelitis

Main Article: Poliomyelitis

Poliomyelitis is more commonly known as polio. Polio is caused by a virus that attacks the nerve cells of the brain and spinal cord, this causes paralysis. [8]

Scoliosis

Main Article: Scoliosis

Scoliosis is side-to-side curve of the spine. It is about two times more common in girls then it is in boys. It can be seen in kids over ten years of age. It is hereditary, so if someones parents have scoliosis then their children are most likely to have it.[9]

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Skeletal System

References

Function

  • De Graaff, Van . "The Skeletal System". 12/24/08 [10]
  • De Graaff, Van. "Joints". 12/24/08 [11]

Organization

  • "longitudinal axis". Answers.com. 12-24-08 [12]

Diseases and Disorders

Development

External links

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