Muscle Tissue Cont. Physiology Chapter 10

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 Pages/Muscle/Muscle.htm#SKELETAL

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)

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

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

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

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 p. 317

Skeletal Muscle Contraction = Sliding Filament Theory

The Contraction Cycle Animation

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

To help you memorize muscles, check out: omy/ omy/ University of Minnesota, WebAnatomy With your laptop, check out: e/mustut.htm e/mustut.htm