PSIO 201 5th Edition Lecture 20Outline of Last Lecture Muscle Contraction CouplingOutline of Current Lecture I. Muscle MechanicsII. Latent PeriodIII. Contraction PeriodIV. Temporal SummationV. Spatial SummationVI. Optimal SummationCurrent Lecture1. 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 TensionB) 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 signalsD) 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 SummationE) Motor Units and the Size Principle- The first motor units recruited are small innervate few fibers- As more forces required more fibers are neededF) Isometric vs. Isotonic Contractions1. Isometric – same length – muscle generates tension but does not shorten2. Every constraction begins isometrically3. Isotonic – same tension- after sufficient tension is generated to move the load the muscle changes in lengthTwo types 1) concentric 2) eccentricG) Concentric vs. Eccentric1. when developed tension is sufficient to move the load, the muscle shortenseffort > load 2. as tension decreases and the load exceeds tension, the muscle lengthens load> effortH) Optimal Muscle length – Length tension relationship* Peak Tension is developed at an
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