Muscle Names Outline

Muscle Names Outline - Chapter 11 The Muscular System I...

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Chapter 11: The Muscular System I. Muscle Organization and Function, p. 327 Muscle organization affects the power, range and speed of muscle movement. Muscle cells or fibers are organized in bundles called fascicles . Skeletal muscles are classified according to the way fascicles are organized, and their relationships to tendons. The 4 patterns of fascicle organization are: 1. parallel 2. convergent 3. pennate 4. circular Most skeletal muscles are parallel muscles . Their fibers parallel the long axis of the muscle. ( e.g. biceps brachii) When a parallel muscle contracts, the center or body of the muscle thickens. Parallel muscles contract about 30% in length. Tension in parallel muscle depends on the total number of myofibrils. Therefore, the cross section of the muscle is directly related to tension. One square inch (6.45 sq. cm) of cross section develops about 50 pounds (23 kg) of tension. Convergent muscles have a broad area that converges on an attachment site such as a tendon, aponeurosis or raphe (a thin band of collagen fibers). Convergent muscle fibers pull in several different directions, depending on which portion of the muscle is stimulated. ( e.g. pectoralis muscles) Pennate muscles form an angle with the tendon, so they do not move as far as parallel muscles. But, pennate muscles contain more myofibrils than parallel muscles, and develop more tension. Pennate muscles can be subdivided into: 1. unipennate : all muscle fibers on 1 side of the tendon ( e.g. extensor digitorum) 2. bipennate : muscle fibers on both sides of the tendon ( e.g. rectus femoris) 3. multipennate : tendon branches within the muscle ( e.g. deltoid) Circular muscles or sphincters open and close to guard entrances of the body ( e.g. obicularis oris) Levers , p. 328 To produce motion, skeletal muscles are attached to the skeleton. Like muscle organization, the type of muscle attachment affects the power, range and speed of muscle movement. Mechanically, each bone is a lever (a rigid, moving structure) and each joint is a fulcrum (a fixed point). The muscles provide the applied force (AF) required to overcome resistance (R). The function of a lever is to change: 1. the direction of an applied force 2. the distance and speed of movement produced by an applied force 3. the effective strength of an applied force There are 3 classes of levers, depending on the relationship between the applied force, the fulcrum, and the resistance:
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first-class lever : - e.g. seesaw - the fulcrum is in the center, between the applied force and the resistance - force and resistance are balanced second-class lever : - e.g. wheelbarrow - the resistance is in the center, between the applied force and the fulcrum - a small force can move a large weight third-class lever : - the most common levers in the body - the applied force is in the center, between the resistance and the fulcrum - requires a greater force to move a smaller resistance, but maximizes speed and distance traveled Most skeletal muscles can shorten
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This note was uploaded on 12/29/2011 for the course BIOLOGY 24011 taught by Professor Pan during the Fall '11 term at HCCS.

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Muscle Names Outline - Chapter 11 The Muscular System I...

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