1. Sensory and Motor Mechanisms Skeletons Interactions between Myosin and Actin Calcium Ions and Regulatory Proteins Control Muscle Contraction

2. Skeletons Function: support, protection, and movement Hydrostatic skeletons-fluid held under pressure, cnidarians, flatworms, nematods, annelids Exoskeletons-hard encasement deposited on the surface of the animal, arthropods Endoskeletons-hard supporting elements buried within the soft tissues of an animal, vertebrates, echinoderms, sponges

3. Structure and Function of Vertebrate Skeletal Muscle Bundle of long fibers running the length of the muscle Each fiber is a single cell with many nuclei, consists of bundles of myofibrils Myofibrils made of thin filaments (two strands of actin) Thick filaments made of myosin

5. Functional Unit-Sarcomere Complex of actin and myosin myofibrils Actin with tropomyosin wrapped around it (tropmyosin is a regulatory protein) Myosin-stationary protein that contains myosin bridges Troponin-protein on tropomysin, binding site for Ca 2+ ions

6. 34.14 The Sliding Filament Model of Muscle Contraction Slide number: 13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sarcomere I bandA bandI band H zone Z line Actin filaments Myosin filaments Contracting Relaxed Fully contracted

9. Sliding Filament Model Myosin myofibrils “pull” actin myofibrils across themselves by the action of myosin bridges and the the interactions of ATP and Calcium ions

10. Muscle Contraction Action potential from axonal knob releases acetylcholine into the T tubule Neurotransmitter binds to the muscle cell Sarcoplamic reticulum releases Ca 2+ Ca 2+ binds to troponin, moving the tropomyosin off of the myosin binding sites

12. Contraction of Muscle ATP is hydrolyzed, joining myosin bridges to the actin Bridges contract, pulling the actin Bridges release, cycle can repeat if ATP present Ca 2+ removed, troponin again blocks the binding sites.

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