Microscopic Anatomy of a Muscle Fiber Copyright 2009

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

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

Microscopic Anatomy of Myofilament Figure 6. 3 c 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 Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings

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

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

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

Microscopic Anatomy of Skeletal Muscle Figure 6. 3 b Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings