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The skeletal system

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Introduction

The precise number of bones in the adult human skeleton varies from one person to another, but on average there are 206 bones varying shapes and sizes. The skeleton is divided into two main parts. The central bones of the skull, ribs, spin (vertebral column) and breast bone (sternum) form the axial skeleton. The bones of the arms and legs, along with the shoulder blade (scapula), collar bone (clavicle) and pelvis make up the appendicular skeleton. The cylindrical, linked vertebrae of the spinal column offer strong, bony protection for the spinal cord. Aided by muscles and ligaments, the vertebrae support the skull and hols the body upright. The spin has a flexible structure that permits twisting and bending of the trunk. The wing-shaped shoulder blades (scapulae) that cover the upper part of the ribcage allow great flexibility in the arms and shoulders. Bone shapes The shapes of the bones reflect their functions. Long bones act as leavers to raise and lower; short bones, such as the ankle bones (talus) are useful bridges; flat bones including those found in the skull form protective shells. Small, rounded, sesamoid bones, such as the knee cap (patella), are embedded within tendons. Irregular bones include vertebrae, the pelvis (ilium), and some skull bones, such as the sphenoid. Bones of the hand and foot The skeletal structure of the hand and foot is similar; in both cases there is an interlinking arrangement of small bones. The hand has 14 finger bones (phalanges) ...read more.

Middle

is protected by the 33 vertebrae of the spinal column Intervertebral disks - composed of though, flexible cartilage with a jelly like core, these disks protect the vertebrae from pressure. Facet joint - this linkage point between the vertebrae is formed by the round ended process of one bone fitting into a matching hollow in the process of the bone above Atlas - this is the top most cervical vertebra to which the skull is attached. Curves of the spine A healthy spine has 4 curves that help to make it resilient and maintain balance. The cervical and lumber section curve forwards, while the thoracic and sacral sections curve back wards. Abnormal curves may be due to poor posture, congenital defect, or bone disease. Reagons of the spine Each section of the spine is adapted to a particular function. The cervical vertebrae support the head and the neck, the thoracic vertebrae anchor to the ribs, and the strong, weight baring regions towards the bottom of the spine provide a sable centre of gravity during movement. Although their shapes vary vertebrae typically comprise a bony disk called the body projections called processes to which muscles attach. Cervical vertebra - a typical cervical vertebra has two wing shaped side processes. A whole through each process allows arteries to pass through and carry blood to the brain. Thoracic vertebra - the thoracic vertebrae form part of the protective rib cage in the thorax. ...read more.

Conclusion

If it is fractured, bone is able to regrow, and eventually the line of fracture is bridged with new tissue. The repair mechanism is activated rapidly after injury, although the laying down of new bone may take weeks to complete. Once mended, a broken bone may take some months to regain its full strength. Joint structure A joint, or articulation, is where two bones meet. Joints are classified by their structure or by the way they move. Most joints in the body are synovial joints. These are versatile, lubricated joints, such as the knee, in which the surfaces in contact slide over each other easily. Articular cartilage covers the bone ends, ligaments provide stability, and fibrous capsule encloses the joint. Surrounding muscles produce movement. Fixed and semi-movable joints Not all joints are freely movable. After growth is complete, the bones of the skull become fixed together by fibrous tissue, forming immovable suture joints, in the lower leg, the tibia and fibula are stabilized by ligaments that allow only a small amount of movement. Types of synovial joint Ina synovial joint, the shape of articular cartilage surfaces and the way they fit together determine the range and direction of the joints movement. Hinge and pivort joints move only in one plane for example from side to side or up and down, while ellipsoidal joints are able to move in two planes at right angles to each other. most joints in the body can move in more than two planes, which allows for a wide range of movements. Diana Hudman Access to H.E: Biology ...read more.

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