Chapter 5: The Muscular System Section 2 Lesson 5.2 Skeletal Muscle Actions Skeletal Muscle • the motor unit • skeletal fiber types • muscular strength, power, and endurance © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. The Motor Unit • group of muscle fibers under the control of one motor neuron © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Generating Action Potentials • acetylcholine crosses the synaptic cleft at the neuromuscular junction • depolarization takes place on muscle fiber • action potential begins © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Contraction of the Sarcomeres • sarcomeres shorten by actin filaments sliding along myosin filaments – INCLUDE THESE 2 LABELED DRAWINGS IN YOUR NOTES! © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Maximum Tension and Return to Relaxation • action potential always causes entire motor unit muscle fibers to contract • all-or-none law © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Review and Assessment True or False? 1. An action potential causes one half of the fibers in the motor unit to contract. 2. Acetylcholine crosses the synaptic cleft at the neuromuscular junction. 3. The sarcomeres lengthen by myosin filaments sliding over actin filaments. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Skeletal Muscle Fiber Types • slow-twitch • fast-twitch – type IIa – intermediate between slow and fast – type IIb – fastest (1/7 the time of slow twitch) © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Skeletal Muscle Fiber Architecture • parallel fiber arrangements – fusiform – bundled – triangular • pennate fiber arrangements – unipennate – bipennate – multipennate © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Muscular Strength • rotary force that muscles can produce at a joint – the maximum weight you can lift is a measurement of muscular strength © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Muscle Power • force x velocity – how fast you can sprint is a measurement of muscle power © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Muscle Endurance • muscle tension/time – how far you can run is a measurement of muscle endurance © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Review and Assessment Match these words with 1–5 below: muscle endurance, muscular strength, muscle power, Type I, Type IIb. 1. force x velocity 2. muscle tension/time 3. rotary force that muscles can produce at a joint 4. slow twitch, slow fatigue 5. fast twitch, fast fatigue © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.