1. Muscle Tissue Cont. Physiology Chapter 10

3. Contraction of Skeletal Muscle = The Sliding Filament Mechanism thin and thick filaments slide past each other to shorten each sarcomere and thus each myofibril the cumulative effect is to shorten the muscle http://www.lab.anhb.uwa.edu.au/mb140/Core Pages/Muscle/Muscle.htm#SKELETAL

4. Skeletal Muscle Innervation The Neuromuscular Junction: where neurons communicate with the muscle fibers point of communication is a small gap = synapse the chemical that travels across the synapse = neurotransmitter (acetylcholine - ACh)

5. Steps of Skeletal Muscle Contraction 1. Neurotransmitter ACh is released from the neuron; binds to its receptor on the sarcolemma, and causes the sodium channels to open

6. Steps of Skeletal Muscle Contraction 2. As Na + ions flow in, an action potential begins action potential = the spread of depolarization 3. ACh removed by enzyme acetylcholinesterase

7. Steps of Skeletal Muscle Contraction 4. Action potential causes release of Ca ++ ions 5. Ca ++ binds to troponin, causing tropomyosin to move out of its blocking position 6. Contraction: myosin forms cross bridges to actin, muscle shortens, ATP is used

8. Steps of Skeletal Muscle Contraction 7. Ca ++ ions are reabsorbed 8. Myosin binds to new ATP 9. Troponin-tropomyosin complex returns to normal position 10. Contraction ends; muscle returns to its resting length STUDY FIG. 10.11 p. 317

10. Skeletal Muscle Contraction = Sliding Filament Theory

11. The Contraction Cycle Animation http://www.sci.sdsu.edu/movies/actin_myosin_gif.html

12. Rigor Mortis When death occurs, Ca ++ ions leak and cause some contraction of the muscles = stiffness Without ATP, cross-bridges cannot detach Lasts ~24 hours, then lysosomal enzymes break down myofilaments

13. To help you memorize muscles, check out: http://msjensen.education.umn.edu/webanat omy/http://msjensen.education.umn.edu/webanat omy/ University of Minnesota, WebAnatomy With your laptop, check out: www.gwc.maricopa.edu/class/bio201/muscl e/mustut.htm www.gwc.maricopa.edu/class/bio201/muscl e/mustut.htm