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md0006 - BASIC HUMAN ANATOMY.pdf - Raems.com

md0006 - BASIC HUMAN ANATOMY.pdf - Raems.com

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a. Trunk Musculature. The trunk musculature is arranged in two<br />

ways--longitudinal muscles and oblique muscles. Together, they:<br />

(1) Maintain trunk posture.<br />

(2) Move the parts of the trunk.<br />

(3) Adjust the internal pressures of the trunk to perform certain functions<br />

such as breathing.<br />

b. Limb Musculature. The limb musculature is arranged around the joints to<br />

produce the appropriate motions of the limbs. Elementary mechanics are described in<br />

the next section to help you to understand typical arrangements of limb musculature.<br />

Section II. SOME ELEMENTARY SKELETO-MUSCULAR MECHANICS<br />

5-5. GENERAL<br />

Muscles and bones together work like machines within the laws of physics and<br />

chemistry. Lever and pulley systems are examples of simple machines found<br />

<strong>com</strong>monly in the human body.<br />

5-6. LEVER SYSTEMS<br />

See figure 5-3 for an illustration of the three classes of levers.<br />

a. First Class. In a first class lever, the weight to be moved is at one end of the<br />

lever, the applied force is at the other end, and the fulcrum (the pivot or turning point) is<br />

between the two.<br />

b. Second Class. In a second class lever, the weight to be moved is between<br />

the applied force and the fulcrum. This type of lever enables a weight to be moved with<br />

less force than would be required without a lever. (Many feel that there are no second<br />

class levers in the human body.)<br />

c. Third Class. In a third class lever, the weight to be moved is at one end of<br />

the lever, the fulcrum is at the other end, and the applied force is between the weight<br />

and the fulcrum. This type of lever provides speed, but a greater amount of force is<br />

required for a given weight. This is the most <strong>com</strong>mon type of lever in the human body.<br />

MD0006 5-6

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