1. Chapter 12 Muscles

2. About this Chapter • Muscle types • What muscles do • How muscles contract • Contraction to locomotion • Roles of smooth muscles

3. Muscles • Contract! • Generate motion • Generate force • Generate heat • Support

4. Muscular System Functions • Body movement (Locomotion) • Maintenance of posture • Respiration • Diaphragm and intercostal contractions • Communication (Verbal and Facial) • Constriction of organs and vessels • Peristalsis of intestinal tract • Vasoconstriction of b.v. and other structures (pupils) • Heart beat • Production of body heat (Thermogenesis)

5. Properties of Muscle • Excitability: capacity of muscle to respond to a stimulus • Contractility: ability of a muscle to shorten and generate pulling force • Extensibility: muscle can be stretched back to its original length • Elasticity: ability of muscle to recoil to original resting length after stretched

6. Muscle Types • Cardiac – heart • Smooth – internal organs • Skeletal – "voluntary" • Attach to bone • Move appendages • Support body • Antagonistic pairs • Flexors • Extensors

7. Categories of skeletal muscle actions • CategoriesActions • Extensor Increases the angle at a joint • Flexor Decreases the angle at a joint • Abductor Moves limb away from midline of body • Adductor Moves limb toward midline of body • Levator Moves insertion upward • Depressor Moves insertion downward • Rotator Rotates a bone along its axis • Sphincter Constricts an opening

8. Types of Muscle • Skeletal • Attached to bones • Makes up 40% of body weight • Responsible for locomotion, facial expressions, posture, respiratory movements, other types of body movement • Voluntary in action; controlled by somatic motor neurons • Smooth • In the walls of hollow organs, blood vessels, eye, glands, uterus, skin • Some functions: propel urine, mix food in digestive tract, dilating/constricting pupils, regulating blood flow, • In some locations, autorhythmic • Controlled involuntarily by endocrine and autonomic nervous systems • Cardiac • Heart: major source of movement of blood • Autorhythmic • Controlled involuntarily by endocrine and autonomic nervous systems

9. Connective Tissue Sheaths • Connective Tissue of a Muscle • Epimysium. Dense regular c.t. surrounding entire muscle • Separates muscle from surrounding tissues and organs • Connected to the deep fascia • Perimysium. Collagen and elastic fibers surrounding a group of muscle fibers called a fascicle • Contains b.v and nerves • Endomysium. Loose connective tissue that surrounds individual muscle fibers • Also contains b.v., nerves, and satellite cells (embryonic stem cells function in repair of muscle tissue • Collagen fibers of all 3 layers come together at each end of muscle to form a tendon or aponeurosis.

10. Muscle Types Figure 12-1: Three types of muscles

11. Muscle Tissue Types

12. Skeletal Muscle Anatomy • About 40% body mass • Muscle fibers – cells • Fascicle – bundle • Motor unit • Muscle • sheath • Attach to tendons (which attach to bone)

13. Nerve and Blood Vessel Supply • Motor neurons • stimulate muscle fibers to contract • Neuron axons branch so that each muscle fiber (muscle cell) is innervated • Form a neuromuscular junction (= myoneural junction) • Capillary beds surround muscle fibers • Muscles require large amounts of energy • Extensive vascular network delivers necessary oxygen and nutrients and carries away metabolic waste produced by muscle fibers

14. Skeletal Muscle Anatomy Figure 12-3a-1: ANATOMY SUMMARY: Skeletal Muscle

15. Skeletal Muscle Anatomy Figure 12-3a-2: ANATOMY SUMMARY: Skeletal Muscle

16. Muscle Fiber Structure • Multiple nuclei • Sarcolemma • T-tubules • Sarcoplasmic reticulum • Sarcoplasm • Mitochondria • Glycogen & ions • Myofibrils

17. Muscle Fiber Structure Figure 12-3b: ANATOMY SUMMARY: Skeletal Muscle

18. Muscle Fiber Structure Figure 12-4: T-tubules and the sarcoplasmic reticulum

19. Myofibrils: Site of Contraction • Actin – "thin fibers" • Tropomysin • Troponin • Myosin – "thick fibers" • Titin – elastic anchor • Nebulin – non-elastic

20. Myofibrils: Site of Contraction Figure 12-3c-f: ANATOMY SUMMARY: Skeletal Muscle

21. Sarcomere: Organization of Fibers • Z disks • I band • A band • H Zone • M line • Titin • Nebulin Figure 12-5: The two- and three-dimensional organization of a sarcomere

22. Sarcomere: Organization of Fibers Figure 12-6: Titin and nebulin

23. Skeletal Muscle Contraction: Mechanism Figure 12-11a: Excitation-contraction coupling

24. Skeletal Muscle Contraction: Mechanism Figure 12-11b: Excitation-contraction coupling

25. Energy for Contraction: ATP & Phosphocreatine • Aerobic Respiration • Oxygen • Glucose • Fatty acids • 30-32 ATPs • Anaerobic Respiration • Fast but • 2 ATP/glucose • Phosphocreatine ATPs

26. Energy for Contraction: ATP & Phosphocreatine Figure 12-13: Phosphocreatine

28. Fiber Contraction Speed: Fast Twitch • Rate • 2-3 times faster • SR uptake of Ca2+ • ATP splitting • Anaerobic/Fatigue easily • Power lifting • Fast/delicate • Sprint

29. Fiber Contraction Speed: Fast Twitch Figure 12-15: Fast-twitch glycolytic and slow-twitch muscle fibers

30. Fiber Contraction Speed: Oxidative Fast & Slow • Oxidative Fast Twitch • Intermediate speed • Anaerobic & aerobic • Slow Twitch: Aerobic, less fatigue • More mitochondria • More capillaries • Myoglobin • Endurance activities • Postural muscles

31. Coordinating the Fibers: Force of Contraction • Excitation and Twitch • Length–Tension: more crossbridges: more tension Figure 12-16: Length-tension relationships in contracting skeletal muscle

32. Coordinating the Fibers: Summation to Tetanus Figure 12-17: Summation of contractions

33. Smooth Muscle • Fusiform cells • One nucleus per cell • Nonstriated • Involuntary • Slow, wave-like contractions

34. Smooth Muscle • Cells are not striated • Fibers smaller than those in skeletal muscle • Spindle-shaped; single, central nucleus • More actin than myosin • No sarcomeres • Not arranged as symmetrically as in skeletal muscle, thus NO striations. • Caveolae: indentations in sarcolemma; • May act like T tubules • Dense bodies instead of Z disks • Have noncontractile intermediate filaments

35. Smooth Muscle • Grouped into sheets in walls of hollow organs • Longitudinal layer – muscle fibers run parallel to organ’s long axis • Circular layer – muscle fibers run around circumference of the organ • Both layers participate in peristalsis

36. Smooth Muscle • Is innervated by autonomic nervous system (ANS) • Visceral or unitary (single unit) smooth muscle • Only a few muscle fibers innervated in each group • Impulse spreads through gap junctions • Whole sheet contracts as a unit • Often autorhythmic • Multiunit: • Cells or groups of cells act as independent units • Arrector pili of skin and iris of eye

37. Smooth Muscle Cell

38. Smooth Muscle Contraction: Mechanism

39. Smooth Muscle Relaxation: Mechanism

41. Contractile fibers are arranged in oblique bundles rather than in parallel sarcomeres

44. Myosin of Smooth Muscle • Different isoform than that found in skeletal muscle • Smooth muscle myosin ATPase activity is much slower, contraction is longer • Myosin light chain in the myosin head regulates contraction and relaxation

45. Smooth Muscle • Relatively little sarcoplasmic reticulum • Lacks T-tubules • Chemically linked to the cell membrane, rather than mechanically linked • Ca +2 storage is supplemented by caveolae , small vesicles that cluster close to the cell membrane. Voltage/ligand gated Ca +2 channels

46. Single-Unit Muscle

47. Gap junctions Pacemaker cells with spontaneous depolarizations Innervation to few cells Tone = level of contraction without stimulation Increases/decreases in tension Graded Contractions No recruitment Vary intracellular calcium Stretch Reflex Relaxation in response to sudden or prolonged stretch Properties of Single-Unit Smooth Muscle

48. Multi-Unit Muscle

49. Comparisons Among Skeletal, Smooth, and Cardiac Muscle