Muscles

1. Muscles

2. Smooth muscle • Found in the walls of hollow organs and the blood vessels • Lack striations • Contain less myosin • Cannot generate as much tension as striated muscle • Can contract over a great range of lengths

3. No T tubule system • No well developed sarcoplasmic reticulum • Contractions are relatively slow

4. Cardiac muscle • Heart muscle • Striated • Electrical properties • Membranes differ • Intercalated discs- junction between cardiac muscle cells • These gap junctions provide direct electrical coupling among cells • Cardiac muscle cells can generate action potentials on their own w/out any input from NS

5. Skeletal muscle • Can only contract (to flex) • Extend passively ( to extend) • Attached to bones • Multi-nucleated muscle fibers (cells) • Fiber- bundle of myofibrils

6. myofibrils • Made up of filaments (myofilaments) • Thick filaments- myosin • Thin- 2 strands of actin and strand one of a regulatory protein • Look like dark and light bands under a microscope

7. Z lines • Borders of sarcomere • Lined up with next myofilaments • Thin filaments are attached to the Z lines • Thick filaments are centered in sarcomere

8. I bands • Area where only thin filaments are found

9. Sarcomere • Unit of thick and thin filaments • Basic unit of muscle

10. A band • Length of thick filaments

11. H zone • Center of A band where only thick filaments are found

14. Contraction • The length of each sarcomere is reduced • the distance between one Z line to the next is shorter • A bands do not change in length, but the I bands shorten • H zone disappears

15. Sliding filament model • Neither thin nor thick filaments change in length; they slide pass each other longitudinally • Therefore the degree of overlap increases • Based on the inter action of myosin and actin

16. Myosin has a “head “ and a “tail” region • Like golf clubs lined up • The head region can bind to ATP • When energized- the myosin takes on a “high energy” configuration • Binds to a site on the actin forming a CROSS-BRIDGE • Stored energy is released • Myosin changes back to a low energy configuration

17. The relaxation changes the angle of attachment of the head to the tail • bends inward • pulls thin filament toward the center of the sarcomere • Bond is broken when a new ATP molecule binds to the myosin head • Process is repeated with the head forming cross-bridge to actin farther down the molecule

18. @350 heads of the myosin filament form and reform @ 5 cross-bridges/ sec. • Only enough ATP is stored for a few contractions • Glycogen is stored in between myofilaments • Most energy is from creatine phosphate- the phosphagen of vertebrates, which can supply a phosphate group to ADP to make ATP

25. http://media.pearsoncmg.com/bc/bc_campbell_biology_6/cipl/ins/49/HTML/source/71.htmlhttp://media.pearsoncmg.com/bc/bc_campbell_biology_6/cipl/ins/49/HTML/source/71.html

26. Control of Muscle Contraction • Skeletal muscle is stimulated by motor neurons • At rest the myosin binding site is blocked by tropomyosin (regulatory protein) • Troponin complex is a set of regulatory proteins that control the position of tropomyosin on the actin

28. Ca ++ bind to troponin, changing the shape of the complex, exposing myosin-binding sites on the actin • Ca++ conc. in cytoplasm is regulated by sarcoplasmic reticulum ( a special type of ER)

29. SR actively transports Ca++ from the cytoplasm to the interior of the SR • An action potential of neuron releases Ca++ • Contraction stops when sarcoplasmic reticulum pumps Ca++ back into storage.

30. Graded contractions of whole muscles • Muscles can contract completely or a little • @ the cellular level, any stimulus that depolarizes the plasma membrane of a single muscle fiber triggers an all-or-none contraction • Therefore a graded contraction is produced when the frequency of the action potential is varied in the motor neurons controlling the muscle

39. Motor unit • Recruitment • Fast muscle fibers • Slow muscle fibers