2. fiber  Each muscle cell is a fiber  Functions of skeletal muscle: ◦ Produce movement ◦ Maintain posture & position ◦ Support tissues ◦ Guard entrances/exits ◦ Maintain body temp ◦ Store nutrients

3. Organization of Connective Tissues  Epimysium perimysium endomysium  Epimysium vs. perimysium vs. endomysium  Blood vessels & enter perimysium; arterioles supply endomysium  Nerve fibers  Nerve fibers penetrate through to endomysium

5. multinucleate  Muscle fibers are large & multinucleate  Sarcolemma sarcoplasm  Sarcolemma surrounds sarcoplasm  Transverse tubules extend into sarcoplasm to conduct impulses

6.  Myofibril myofilament  Myofibril vs. myofilament  Myofilaments  Myofilaments: ◦ Thin filaments ◦ Thin filaments (actin) ◦ Thick filaments ◦ Thick filaments (myosin)  Myofibrils contract to shorten muscle fiber

8. Sarcomeres sarcomeres  Myofibrils arrange in sarcomeres  A bands  A bands (dark) contain thick & thin filaments ◦ M line ◦ M line connects thick filaments  I bands  I bands (light) contain thin filaments ◦ Z line ◦ Z line marks boundary of sarcomere

9.  Thin filament contains twisted actin strands ◦ Active sites ◦ Active sites bind to myosin ◦ Tropomyosin ◦ Tropomyosin blocks active site at rest  Thick filament contains myosin molecules cross-bridges ◦ Myosin heads form cross-bridges when join thin filaments

11. Sliding Filament & Contraction  Sliding filament theory  Sliding filament theory of contraction: ◦ I band gets smaller ◦ Zone of overlap gets larger ◦ Z lines move closer together ◦ A band width remains constant  Muscle fiber shortens & contracts, pulling muscle

12. neuromuscular junction  Nervous system & muscle fiber connect at neuromuscular junction ◦ Examine Figure 10-11 (pg 292-293)  Excitation-contraction coupling ◦ Release of Ca + causes troponin to open active sites on actin

13.  Contraction cycle ◦ Examine Figure 10-12 (pg 294-295) ◦ Formation & detachment of cross-bridgesRelaxation  Contraction continues until action potential, Ca +, and/or ATP reserves are gone  Muscle fiber returns to original length

14. Tension & Muscle Fibers  Max tension ◦ Large zone of overlap, thin filaments don’t contact center of sarcomere  No tension ◦ Thick filaments contact Z lines, OR no zone of overlap  More cross-bridges = more tension

15.  Twitch  Twitch = stimulus-contraction- relaxation sequence ◦ Latent period contraction period relaxation period ◦ Latent period vs. contraction period vs. relaxation period treppewave summationincomplete tetanus complete tetanus  Repeated stimulations: treppe, wave summation, incomplete tetanus, complete tetanus

16.  Motor uni  Motor unit—all fibers controlled by a motor neuron ◦ Recruitment ◦ Recruitment adds more muscle fibers Muscle Tone  Some motor units remain active & provide muscle tone  Requires energy even at rest

17. creatine phosphate  Muscles use creatine phosphate & ATP for energy Aerobic Metabolism citric acid cycle electron transport chain  Mitochondria use citric acid cycle & electron transport chain to provide 95% of needed ATP

18. Anaerobic Metabolism  Glycolysis  Glycolysis breaks down glucose from glycogen stores ◦ Provides ATP during periods of high muscle activity ◦ Lactic acid ◦ Lactic acid produced  Muscle fatigue: low oxygen, blood pH  Recovery  Recovery—muscle fibers return to pre-exertion condition

19. Types of Skeletal Muscle Fibers  Fast fibers slow fibers intermediate fibers  Fast fibers vs. slow fibers vs. intermediate fibers  Hypertrophy atrophy  Hypertrophy vs. atrophy  Anaerobic endurance aerobic endurance  Anaerobic endurance vs. aerobic endurance

20. intercalated discs  Single nucleus, typically branched, intercalated discs  Completely dependent on aerobic metabolism automaticity pacemaker cells  Have automaticity through pacemaker cells

21.  Found in sheets in many body systems nonstriated  Cells spindle-shaped & nonstriated  Contract over wide range of lengths (plasticity)  Multiunit visceral  Multiunit vs. visceral smooth muscle