Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Muscle Contraction

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of Skeletal Muscle  Sarcomere  Contractile unit of a muscle fiber Figure 6.3b

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of Skeletal Muscle  Sarcomere  Thick filaments = myosin  Thin filaments = actin  Has ATPase enzymes Figure 6.3c

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Stimulation by nerve impulses Skeletal muscle must be stimulated by nerve impulses to contract MOTOR UNIT = 1 neuron + skeletal muscle cells it stimulates AXON = extension of neuron  Branches into AXON TERMINALS

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Stimulation by nerve impulses Axon terminals form junctions (NEUROMUSCULAR JUNCTIONS) with the sarcolemma of different muscle cell Nerve and muscle cell membrane never touch, although very close Gap called SYNAPTIC CLEFT that is filled with interstitial fluid

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Contraction 1.Nerve impulse reaches axon terminals 2.Neurotransmitter Ach stimulates skeletal cells 3.ACETYLCHOLINE (Ach) diffuses across synaptic cleft and attaches to protein receptors on the cell membrane 4.Sarcolemma (ie: like cell membrane) increases permeability 5.Na+ goes in….K+ goes out of the cell  >Na+ than K+ inside  Imbalance creates an electrical current = ACTION POTENTIAL 6.Action potential spreads from 1 end of cell to other = CONRACTION (ie: single nerve = 1 contraction)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Post-Contraction 1.K+ moves out of cell 2.Na+/K+ pump on membrane moves Na+ and K+ back to normal 3.ACh is broken down

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of Skeletal Muscle  Myosin filaments have heads (extensions, or cross bridges)  Myosin, actin overlap Figure 6.3d

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of Skeletal Muscle  At rest, there is a bare zone that lacks actin filaments Figure 6.3d

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 1.Myosin head attaches to binding sites of thin filaments when muscle fibers are activated by nervous system…requires Ca 2+  TROPININ on actin has binding site for Ca 2+  TROPOMYOSIN on actin covers myosin head binding site on actin 2.Each myosin cross bridge attaches and detaches during a contraction  muscle cell shortens 3.Myosin heads rotate creating a “power stroke” (ie: the sliding) 4.ATP releases myosin from actin 5.Contraction continues if ATP is available and Ca 2+ in sarcoplasm is high  If not…muscle relaxes 6.**ATP is responsible for moving Ca 2+ back to original place (sarcoplasmic reticulum) Figure 6.7 SLIDING FLIAMENT THEORY

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings