Chapter 12a Muscles 2013 Pearson Education Inc About This Chapter Skeletal muscle Mechanics of body movement Smooth muscle Cardiac muscle 2013 Pearson Education Inc Figure 12 1a 4 of 6 Skeletal muscle fibers are large multinucleate cells that appear striped or striated under the microscope Nucleus Muscle fiber cell Striations Figure 12 1b 5 of 6 Cardiac muscle fibers are also striated but they are smaller branched and uninucleate Cells are joined in series by junctions called intercalated disks Nucleus Muscle fiber Intercalated disk Striations Figure 12 1c 6 of 6 Smooth muscle fibers are small and lack striations Nucleus Muscle fiber Skeletal Muscle Usually attached to bones by tendons Origin closest to the trunk or to more stationary bone Insertion more distal or more mobile attachment Flexor brings bones together Extensor moves bones away Antagonistic muscle groups flexor extensor pairs Satellite cells differentiate into muscle 2013 Pearson Education Inc Figure 12 2a 1 of 2 Triceps muscle relaxes Biceps muscle contracts flexor Flexion moves bones closer together Figure 12 2b 2 of 2 Triceps muscle contracts extensor Biceps muscle relaxes Extension moves bones away from each other Figure 12 3a 1 ANATOMY SUMMARY Skeletal Muscles Skeletal muscle Tendon Nerve and blood vessels Connective tissue Muscle fascicle bundle of fibers Connective tissue Nucleus Muscle fiber Figure 12 3a 2 ANATOMY SUMMARY Skeletal Muscles SKELETAL MUSCLE composed of Muscle fascicles composed of individual Muscle fibers cells which contain Connective tissue Blood vessels Nerves Sarcoplasm Multiple nuclei Sarcolemma T tubules T tubules are functionally linked to Sarcoplasmic reticulum Myofibrils composed of Mitochondria Glycogen granules Troponin Actin Tropomyosin Myosin Titin Nebulin Thin filaments Thick filaments T tubules are a continuation of the sarcolemma organized into Sarcomere Table 12 1 Muscle Terminology Figure 12 3c f ANATOMY SUMMARY Skeletal Muscles A band Sarcomere Z disk Z disk ANATOMY SUMMARY Myofibril M line I band H zone Titin Z disk M line Myosin crossbridges Z disk Thick filaments M line Thin filaments Myosin heads Myosin tail Hinge region Myosin molecule Titin Troponin Nebulin Tropomyosin G actin molecule Actin chain Figure 12 3b ANATOMY SUMMARY Skeletal Muscles ANATOMY SUMMARY Sarcoplasmic reticulum Nucleus T tubules Sarcolemma Mitochondria Thick filament Thin filament Myofibril Figure 12 4 T TUBULES T tubules are extensions of the cell membrane sarcolemma that associate with the ends terminal cisternae of the sarcoplasmic reticulum T tubule brings action potentials into interior of muscle fiber Sarcoplasmic reticulum stores Ca2 Sarcolemma Triad Thick filament Thin filament Terminal cisterna Figure 12 3e ANATOMY SUMMARY Skeletal Muscles ANATOMY SUMMARY Thick filaments M line Myosin heads Myosin tail Hinge region Myosin molecule Figure 12 3f ANATOMY SUMMARY Skeletal Muscles ANATOMY SUMMARY Thin filaments Titin Troponin Nebulin Tropomyosin G actin molecule Actin chain Figure 12 3d ANATOMY SUMMARY Skeletal Muscles ANATOMY SUMMARY Titin Z disk M line Myosin crossbridges Z disk Figure 12 3c ANATOMY SUMMARY Skeletal Muscles ANATOMY SUMMARY A band Sarcomere Z disk Z disk Myofibril M line I band H zone Figure 12 5 1 ESSENTIALS The Sarcomere Organization of a Sarcomere The Z disk not shown in part c has accessory proteins that link the thin filaments together similar to the accessory proteins shown for the M line Myosin heads are omitted for simplicity I band I band Sarcomere A band H zone i k s d Z e n i l M i k s d Z KEY Actin Myosin I band Actin only H zone Myosin only M line A band Myosin linked with accessory outer edge Actin and myosin proteins overlap Figure 12 6 TITIN AND NEBULIN Titin and nebulin are giant accessory proteins Titin spans the distance from one Z disk to the neighboring M line Nebulin lying along the thin filaments attaches to a Z disk but does not extend to the M line Nebulin helps Z disk align actin Z disk Actin M line Titin provides elasticity and stabilizes myosin Myosin Muscle Contraction Muscle tension force created by muscle Load weight or force opposing contraction Contraction creation of tension in muscle Relaxation release of tension Sliding filament theory 2013 Pearson Education Inc Figure 12 7 SUMMARY MAP OF MUSCLE CONTRACTION Events at neuromuscular junction Excitation contraction coupling Ca2 signal Contraction relaxation cycle This icon represents a map of the events in muscle contraction Look for this icon throughout this chapter as these events are explored in greater detail Muscle twitch Sliding filament theory Events at the Neuromuscular Junction A P FlixTM Events at the Neuromuscular Junction 2013 Pearson Education Inc Figure 12 5 2 ESSENTIALS The Sarcomere The Sarcomere Shortens During Contraction As contraction takes place actin and myosin do not change length but instead slide past one another I band A band Muscle Relaxed Sarcomere shortens with contraction Muscle Contracted H zone and I band both shorten while A band remains constant Half of I band H zone Half of I band Myosin Actin Z line I H I Skeletal Muscle Tissue Interactive Physiology Animation Anatomy Review Skeletal Muscle Tissue 2013 Pearson Education Inc Figure 12 8a 1 of 7 Relaxed state Myosin head cocked Tropomyosin partially blocks binding site on actin Myosin is weakly bound to actin Troponin G actin Tropomyosin Myosin head TN ADP Pi Figure 12 8b 2 of 7 Initiation of contraction A calcium signal initiates contraction Cytosolic Ca2 Tropomyosin shifts exposing binding site on actin Actin moves TN Power stroke ADP Pi Ca2 levels increase in cytosol Ca2 binds to troponin TN Troponin Ca2 complex pulls tropomyosin away from actin s myosin binding site Myosin binds strongly to actin and completes power stroke Actin filament moves Figure 12 8b 2 of 7 Cytosolic Ca2 Slide 1 Ca2 levels increase in cytosol TN ADP Pi 2013 Pearson Education Inc Slide 2 Ca2 levels increase in cytosol Ca2 binds to troponin TN Figure 12 8b 2 of 7 Cytosolic Ca2 TN ADP Pi 2013 Pearson Education Inc Figure 12 8b 2 of 7 Slide 3 Cytosolic Ca2 Tropomyosin shifts exposing binding site on actin TN ADP Pi Ca2 levels increase in cytosol Ca2 binds to troponin TN Troponin Ca2 complex pulls tropomyosin away from actin s myosin binding site 2013 Pearson Education Inc Tropomyosin shifts exposing binding site on actin Slide 4 Ca2 levels increase in cytosol Ca2 binds to troponin TN Troponin Ca2 complex pulls tropomyosin away from actin s