PSIO 201 5th Edition Lecture 20 Outline of Last Lecture Muscle Contraction Coupling Outline of Current Lecture I Muscle Mechanics II Latent Period III Contraction Period IV Temporal Summation V Spatial Summation VI Optimal Summation Current Lecture 1 The Muscle Twitch contraction arising from a single electrical stimulus an action potential 3 Periods 1 The Latent Period no tension change 2 The Contraction increasing tension 3 Relaxation decreasing tension A The Latent Period lasts 2 msec or less Action potential sweeps over the sarcolemma Calcium ions released from the sarcoplasmic reticulum No Change in Tension B Contraction Period Lasts 10 100 msec or less Calcium binds to Troponin Myosin binding sites on actin are exposed Crossbridges form and swivel Peak tension Develops C Muscle Mechanics Tetanus tetanic contraction Summation over time of individual twitches Twitch Wave summation unfused tetanus Fused tetanus Tensions Temporal summation how body creates tension by nervous system signals D Tension Production and the Motor Unit Motor Unit a motor neuron and all the muscle fibers it innervates Muscles typically contain many motor units By activating recruiting increasing numbers of motor units tension can be increased Spatial Summation E Motor Units and the Size Principle The first motor units recruited are small innervate few fibers As more forces required more fibers are needed F 1 2 3 Isometric vs Isotonic Contractions Isometric same length muscle generates tension but does not shorten Every constraction begins isometrically Isotonic same tension after sufficient tension is generated to move the load the muscle changes in length Two types 1 concentric 2 eccentric G Concentric vs Eccentric 1 when developed tension is sufficient to move the load the muscle shortens effort load 2 as tension decreases and the load exceeds tension the muscle lengthens load effort H Optimal Muscle length Length tension relationship Peak Tension is developed at an intermediate
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