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| Movements |
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| Movements of bones occur only at the joints. The movements are brought about by contractions of skeletal muscles inserted onto the articulating bones by firm cords of white fibrous tissue called tendons. Cords of yellow elastic tissue, termed ligaments, stabilise the joints by holding the articulating bones together. |
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| The movements taking place at the skeletal joints may be divided into three principle groups. |
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| i. Gliding movements in which two flat surfaces move on each other as occurs in the movements between the carpal and tarsal bones. |
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| ii. Angular movements, which is described according to the direction in which the movement takes place, example flexion- a bending , extension- a stretching or straightening out takes place around an axis which is transversely placed. Adduction is that movement which is towards the medial aspect of the body, and abduction, which is in a direction away from the medial aspect of the body and takes place round an axis running from front to back. |
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| iii. Rotation movements are those in which one bone moves around or within another bone as in the pivot joints. |
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| Example: The rotation of radius on ulna. |
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| Circumduction is the term used to describe a combination of rotation and angular movements. |
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| Example: The carrying of the arm forward, upward, backward and down ward movements. |
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| Role of Muscles and Bones in Movement |
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| The muscles in the body provide the means of all movements. When stimulated by a nerve, the muscle contracts to become shorter and thicker and thus it pulls the bone at the movable end. Most actions in our body like standing, walking, running, playing etc. require combined action of several muscles. Movements of different parts of the body are usually made easier due to leverage actions in the skeleton. Functioning of all the three types of levers can be observed in the human skeleton. |
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| (a) (b) (c) |
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| Roles of bones and muscles in movement: (a) joint between first vertebra and skull on the principle of first class lever (b) Human body resting on toe as second class lever (c) Elbow joint of forearm as third class lever |
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| 1) Levers of first order |
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| In these, the fulcrum is in the centre with weight and power on either side. For example, the joint between the first vertebra (atlas) and occipital bone of skull exhibits first class lever, in which the joint is the fulcrum, contraction of back muscle in the effort and facial part of the skull on raised head acts as the weight or resistance. |
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| 2) Levers of the second order |
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| In this the weight is in the middle between the power and the fulcrum. For example human body resting on toes. Here the toe forms the fulcrum and contracting calf muscle provides effort. |
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| 3) Levers of the third order |
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| Here the power is in the middle and the weight and fulcrum on either side. For example the flexing of the elbow of forearm. Here the elbow joint acts as fulcrum, and the distal part of hand provide resistance. |
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| The contracting biceps muscles exert the effort in between fulcrum and resistance. |
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