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Our bodies are built upon a frame called the skeleton. The skeleton is made up of several bones. Bones that can move connect with other bones at joints. From now on we shall generally imply movement bones when we use the word bones. Joints allow connected bones to move with respect to each other. The movement is a rotation about the joint. Different joint types allow differing freedom to the movement both in terms of distance and directions. Some joints allow movement in only one plane, some allow more.
Bones between two joints (usual a single bone but sometimes more, e.g. forearm) form the basis of a body segment. Each body segment is supported by its bone(s) and moves as the bone rotates around the connecting two joints. When describing a collection of body segments the terms distal and proximal are sometimes used. These two words describe the position of a body segment with regards to a reference point (often the centre of the body). Proximal is towards the the reference whilst distal is away from the reference point. For example, when the reference point is the centre of the body, the abdominal region is proximal whilst the hands and feet are distal. Also, with the same reference point, the forearm is proximal to the hand, or put another way, the hand is distal to the forearm.
Joints are supported with ties called ligaments. Ligaments help prevent movements that the joint is not designed for. Cartilage is used in joints as a shock absorber. Synovial fluid is the lubricant around the whole the whole system that substantially reduces friction.
The motor of the system is the skeletal muscle. These connect to the bones via tendons and generate the force to create movement in the system. Skeletal muscles are used to:
In the next section we look at how muscles generate and affect movement.
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