1. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of a Muscle Fiber

2. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of a Muscle Fiber  Sarcolemma—specialized plasma membrane  Sarcoplasm- cytoplasm of muscle cells; contains large amounts of stored glycogen and an oxygen-binding protein, myoglobin  Sarcoplasmic reticulum— specialized smooth endoplasmic reticulum Stores and releases calcium Surrounds the myofibril

3. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of a Muscle Fiber  Myofibrils- long organelles inside muscle cell extending the entire length of the cell; hundreds to thousands in each fiber/cell (80% of cell volume)

4. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of the Myofibril  Sarcomere— repeating unit along the myofibril contractile unit of a muscle fiber made of myofilaments

5. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of the Sarcomere  Myofilaments  2 Types in a sarcomere 1.Actin filaments Thin filaments  Composed of the protein actin  Anchored to the Z disc (which is a membrane)

6. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of the Sarcomere 2. Myosin filaments Thick filaments =  Composed of the protein myosin  Has ATPase  Myosin filaments have heads (extensions, or cross bridges)  Myosin and actin overlap somewhat

7. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of Myofilament Figure 6.3c

8. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of Skeletal Muscle  Myofilaments are aligned to give distinct bands  I band = light band  Contains only actin (thin) filaments  A band = dark band  Contains the entire length of the mysosin (thick) filaments

9. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings

10. Microscopic Anatomy of the Sarcomere striations - repeating series of dark and light bands A bands- dark bands -H zone- lighter stripe in midsection of an A band; visible when muscle is relaxed -M line- dark line bisecting each H zone I bands- light bands - Z line- dark line bisecting each I band

11. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscle relaxed- H zone easy to see

12. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of Skeletal Muscle Figure 6.3b