This paper aims to look at the anatomy and physiology of the Skeletal system. This area of study can be looked in a several distinct parts. The structure and development of bones; The structure and classification of Synovial joints; and the structure of the spinal column. Each of these aspects of skeletal physiology also have implications in the prescription of exercise, and some examples of this will be also discussed.
There are 5 main bone types in the human skeleton. Long bones, short
bones, flat bones, irregular bones and sesamoid bones. A sixth type
known as “Wormian” bones is also found, which are found during growth of
the skull in children, these will not be discussed.
These varieties in size and shape are all due to the different functions these bones carry out. However, they all follow a similar structure, a variation on a theme. They must all be strong enough to support us, and light-weight enough so we can move. This is achieved by having the hardest area of bone, called compact bone, on the outside, forming a rigid cylinder called the Diaphysis, and looser, spongy tissue, known as cancellous bone inside the head. Between the cancellous bone and the interior of the shaft, or Medullar cavity, are plates. These Epiphyseal plates are part of the development process of the bone, and are discussed in more detail later.
Within the medullar cavity is yellow bone marrow. This is where vital minerals, and calcium are stored. Red marrow is found within the cancellous bone at each end, and this manufactures red blood cells. On the very outside of the bone is found the periosteum. This is a protective layer round the bones, that provides the attachment for ligaments and tendons. At the point of contact with other bones is found Articular cartilage. This provides a frictionless, cushioning coating to prevent the bones from wearing each other away. Failure of the cartilage is what causes arthritis.
In the foetus, the skeleton is first laid down as cartilage, but as development continues, it is replaced by bone in a process known as ossification. This is a complex process involving the gradual removal of cartilage by cells from outside which invade it; other cells of a different kind then follow and lay down the bone which eventually replaces the cartilage that has been removed.
In an X-ray of a bone, it is possible to see where cartilage is still present (At the Epiphyseal plates), these are the places where growth in length is still taking place, and it is possible to estimate a child’s age from the size of these regions.
Because children have a greater percentage of cartilage in their bones
than adults, their bone structure is significantly more flexible than adults.
This means that, in the event of a fracture, the bone will bend and splinter,
rather than snap. In the case of exercise and sport, the bones must
not be over loaded, or else longitudinal growth may be reduced, resulting
in pain, and stunted growth in later life. Weight training should
not be carried out by children until their development has slowed.
It is not the age, or size of the child that is important, rather than
their developmental stage.
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At any point in the body, where two bones meet, there will be a joint
of sorts. The most common joint is the Synovial joint. These
joints are freely moving, and allow efficient transfer of muscular force
from one muscle to bone and to bone.
There are a number of different types of Synovial joint, these are
typically...
The ends of the bones in Synovial joints are shaped to fit each other in such a way as to limit their movement in the directions required. Range and direction of movement is aided and controlled by ligaments, that attach the bones together. On the surface of the bone is the Articular cartilage, which aids movement, and reduces wear on the bone face. Surrounding the whole joint is the “Joint Capsule”. This contributes to the control and stability of the joint, along with the ligaments. It is attached to the periosteum, tough and stretch resistant. Within this capsule is the Synovial membrane from which the joint gets its name. this secretes Synovial fluid into the joint, which aids in reducing friction. Between tendons and bone, in certain joints, little pads known as bursae can be found. These offer a “bridge” for the tendon to move over, reducing friction and wear between the tendon and the bone itself.
As was mentioned in the description of the structure of the joint, the
shape of fit of the bones and the tendons restrict mobility of the joint
to within required constraints. There are a number of other factors
that also affect the range of motion, or ROM, of a joint. The most
obvious restrictions are structural, bony protrusions around the joint,
like where the point of the elbow fouls the humerous, limiting its movement.
The joint structure itself, with the ligaments, joint capsule and face
of bones.
Temperature plays a major role in ROM. Quite simply, the warmer
the joint is, the greater its ROM will be, this places great emphasis on
doing a proper warm-up before exercise. Stretching is important to
athletes. This is because as muscles become more and more trained,
they tend to shorten slightly, thus restricting mobility. However,
good muscle structure also add to the stability of many joints, like the
knee. As we age, our body’s ability to function decreases.
this includes flexibility. Older people don’t have the same strength
as the young.
The Skeleton can be split into two distinct areas, the appendecular skeleton and the axial skeleton. The appendicular skeleton comprises the limbs, and the axial comprises the ribs, and spinal column. The Spinal column is what will be discussed here.
The spine is made up of a curved stack of 33 irregular bones, known as vertebrae. This stack can be divided into 5 regions which are, from the top, cervical (7 vertebrae), thoracic (12 vertebrae), Lumbar (5 vertebrae), sacral (5 fused vertebrae) and coccygeal (4 fused vertebrae). Two adjacent vertebrae, and all the soft tissue between them make up one “Motion segment”. The vertebrae are irregular in shape, with the spinal cord running down the “neural arch” or the vertebrae. Between each vertebrae is a intervertebral disc. This is a fibrocartilaginous disc, that cushions the two bones.
The spine is curved to enable it to absorb shock more easily, however, improper loading can exaggerate this curve in certain regions, resulting in conditions such as... Lordosis, where the lumbar region is excessively curved, Kyphosis, where the thoracic region is exaggerated, or scoliosis, which is a lateral curve in the spine, the one plane that should be straight.
Preventing injury of the spine is simple, yet thousands of people injure their back every year through bad practices. By carrying loads too far from their trunk, the levering action of the bones places great load on the lower back, resulting in, lower back pain. This can be diagnosed as being many things, each of which requiring extensive explanation. Incorrect posture puts uneven extra loads on the back muscles, this can cause distortion of the spine. This can lead to, in later life, joint and muscle and joint disorders, that can cause much pain.
The Skeleton has 2 main functions, to protect, support and provide a means of motion. In doing so, these parts of our bodies require many features, some of which have been discussed herein. It becomes apparent from study that the skeletal system of our bodies is vital not just for support or movement, but for our comfort and growth. Good practice now is probably the best insurance we can have against joint injury and “Aches and pains” in later life
Course texts. Falkirk College 1997/8
Biology for Today., Neal & Neal, 1983
Physiology of sport and Exercise, Wilmore and Costill, 1994