Skeletal System 5

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Skeletal System 5...

Skeletal System 5:

The largest bone in the foot is the calcaneus or the heel bone. Think of how much time you spend on your feet. Then think of the structure and size of your feet. Isn't it interesting to think that this relatively small structure can withstand the wear and tear of our day to day activities?

The foot bones are held together by strong ligaments and leg muscles that allow us to have a good deal of flexibility while being strong and providing a stable base.

When our ligaments weaken we refer to this as fallen arches or flat feet.

JOINTS

Joints are the point of contact between two bones. They are classified into 3 main types according to their degree of movement.

DIARTHROSES- movable joints

AMPHIARTHROSES- partially movable joints

SYNARTHROSES- immovable joints

Diarthroses - Most of the joints in our body are diarthroses. They tend to have the same structure. These joints allow for considerable movement sometimes in many directions and sometimes in only one or two directions. These movable joints consist of three main parts: articular cartilage, a bursa or a joint capsule and a synovial or joint cavity.

When 2 movable bones meet at a joint their surfaces do not touch one another. The two articular surfaces are covered with a smooth slippery cap of cartilage called the articular cartilage. This cartilage helps to absorb jolts.

Enclosing the 2 articular surfaces of the bone is a tough, fibrous connective capsule called a joint capsule or an articular capsule. Lining the articular capsule is a synovial membrane which secretes synovial fluid. The synovial fluid reduces the friction of the 2 articulating surfaces.

The structure of the joint capsule makes the joint function. Ligaments grow out of the periosteum and connect the bones together more firmly.

The clefts in connective tissue between muscles,tendons, ligaments and bones contain bursa sacs. If the bursa becomes irritated or injured a condition known as bursitis develops. The synovial fluid can be aspirated from the bursal sacs and examined for diagnostic purposes. Typical examinations may include a culture and sensitivity and a micro exam to check for

WBC’s and RBC’s.

As we advance in age the joints undergo degenerative changes. The synovial fluid is not secreted as quickly and the articular cartilage’s become ossified. This results in bone outgrowths along the joint edges which tend to stiffen joints causing inflammation, pain and a decrease in mobility.

There are several types of diarthroses joints: ball and socket, hinge, pivot and gliding and condyloid joints. Because they differ in structure they also differ in the amount of movement and range of motion.

Ball and socket joints- These joints allow for the greatest freedom of movement. One bone has a ballshaped head which nestles into a concave socket of the second bone. Examples are hip and shoulder joints.

Hinge joints are like hinges on a door. They allow movement in only two directions namely flexion and extension. Examples of a hinge joints are the knees, elbows and the outer joints of the fingers.

Pivot joints are those with an extension rotating in a second, arch shaped bone. The radius and ulna, wrist and ankle joints are all pivot joints. An example of this joint is between the atlas or the first cervical vertebrae which supports the head and the axis or the second cervical vertebrae which allows the head to rotate.

Gliding joints are those in which nearly flat surfaces glide across each other as in the vertebrae or the spine. These joints enable the torso to bend forward, backward, sideways as well as rotate.

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