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Unformatted text preview: C - 102Dr. Kennon M. Garrett MUSCLE MECHANICS; SMOOTH MUSCLE Reading: Widmaier et al., Vanders Human Physiology, 12th ed., pp. 263-267, 271-273, 279-285. Behavioral Objectives 1. Define tension, load, isometric contraction and isotonic contraction. 2. Describe how changing the load on a muscle fiber affects the velocity of contraction. 3. Describe how changing the frequency of stimulation affects muscle tension. 4. Describe how changing the initial length of a muscle fiber affects the cross bridge alignment and how this affects muscle tension. 5. Describe how recruitment of motor units affects tension in the whole muscle. 6. Compare the microanatomy of smooth muscle with skeletal muscle. 7. List the steps of excitation-contraction coupling in smooth muscle and how it differs from skeletal muscle. 8. List the sources of Ca2+used for contraction in smooth muscle. I. Twitch contractionsA. Forces 1. Tension - force exerted by muscle on object 2. Load - force exerted by object on muscle B. Types of contractions During a contraction cross-bridge cycling occurs to develop tension. The muscle fiber will shorten only if the tension is greater than the load.1. Isometric- load is equal to or greater than tension, no shortening, constant length of muscle. Tension is measured during isometric contractions 2. Isotonic- tension is greater than load, muscle shortens, constant tension. Lengthis measured during isotonic contractions.(Fig 9-16b) 3. Lengthening contraction load is greater than the tension on an unsupported muscle. The length of the muscle increases even though the muscle is contracting. C - 103Figure 9-16 II. Single-fiber mechanicsA. Contraction time 1. Twitch contraction of a muscle fiber in response to a single action potential 2. Isometric twitch keep length constant and measure tension The latency of contraction is the time between action potential and development of tension. This time is due the time of excitation-contraction coupling....
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- Fall '11