Muscular Control of Movement Chapters 17 and 18

1. Muscular Control of MovementChapters 17 and 18 Review of Gross Anatomy: • 430 voluntary muscles in the body. • The muscle is • 75% water, • 20% protein, • and 5% inorganic salts and other substances.

2. Types of Muscles: • 1. Smooth - blood vessels and organs. • 2. Cardiac - heart. • 3. Skeletal - movement muscles.

3. Origins and Insertions • The origin of the muscle is the relatively stable skeletal part to which the muscle attaches. • This is usually more proximal.

4. Origins and Insertions • The insertion of the muscle is the more mobile skeletal part to which the muscle attaches and is more distal.

5. Connective Tissue Components

6. The Structure and Function of Skeletal Muscle • An individual muscle cell is called a muscle fiber. • A muscle fiber is enclosed by a plasma membrane called the sarcolemma.

7. Sarcolemma

8. The Structure and Function of Skeletal Muscle: • The cytoplasm of a muscle fiber is called the sarcoplasm. • The extensive tubule network found in the sarcoplasm includes: • t-tubules - allow communication and transport of substances throughout the muscle fiber • sarcoplasmic reticulum - which stores calcium.

9. Sarcoplasm

10. The Structure and Function of Skeletal Muscle: • Myofibrils are composed of sarcomeres, the smallest functional units of muscle. • A sarcomere is composed of filaments of two proteins, which are responsible for muscle contraction.

11. The Structure and Function of Skeletal Muscle: • Myosin is a thick filament, folded into a globular head at one end. • An actin filament is composed of actin, tropomyosin, and troponin.

14. The Structure and Function of Skeletal Muscle: • One end of each actin filament is attached to a z disk.

15. Sarcomere: • The bands are named according to their optical properties. • The I band (isotropic) - velocity of light is same in all directions. • Contains actin only.

16. Sarcomere: • A band (anisotropic) - light does not scatter equally. • Contains both actin and myosin. • Z disk (zwischen) - German word for between.

18. Sarcomere: • H zone - center of A band. • Contains myosin only.

19. The Sliding Filament Theory: • Muscle action is initiated by a motor nerve impulse.

20. The Sliding Filament Theory: • The action potential travels along the sarcolemma, then through the tubule system, and eventually causes stored calcium to be released from the sarcoplasmic reticulum.

22. The Sliding Filament Theory: • Calcium binds with troponin, and then troponin lifts the tropomyosin molecules off of the active sites on the actin filament, opening these sites for binding with the myosin head.

23. The Sliding Filament Theory: • Once it binds with the actin active site, the myosin head tilts, pulling the actin filament so that the two slide across each other. • The tilting of the myosin head is the power stroke.

26. The Sliding Filament Theory: • Energy is required before muscle action can occur. • The myosin head binds to ATP, and ATPase found on the head splits ATP into ADP and Pi, releasing energy to fuel the contraction.

27. The Sliding Filament Theory: • Muscle action ends when the calcium is actively pumped out of the sarcoplasm back into the sarcoplasmic reticulum for storage. • This process, leading to relaxation, also requires energy supplied by ATP.

28. Skeletal Muscle and Exercise • Most skeletal muscles contain both ST and FT fibers.

30. Skeletal Muscle and Exercise: • The different fiber types have different ATPases. • The ATPase in the FT fibers acts faster, providing energy for muscle action more quickly than the ATPase in ST fibers.

31. Skeletal Muscle and Exercise: • FT fibers have a more highly developed sarcoplasmic reticulum, enhancing the delivery of calcium needed for muscle action.

32. Skeletal Muscle and Exercise: • Motor neurons supplying FT motor units are larger and supply more fibers than do neurons for ST motor units. • Thus FT motor units have more fibers to contract and can produce more force than ST motor units.

33. Skeletal Muscle and Exercise: • The proportions of ST and FT fibers in an individual’s arm and leg muscles are usually quite similar.

34. Skeletal Muscle and Exercise: • ST fibers have high aerobic endurance and are well suited to low-intensity endurance activities.

35. Skeletal Muscle and Exercise: • FT fibers are better for anaerobic activity. • FTa fibers are well utilized in explosive bouts of exercise.

36. Skeletal Muscle and Exercise: • Fiber type is predominantly determined by genetics. • Composition will change over the course of your life as FT fibers atrophy and die.

37. Classification of Muscle Fibers • Characteristic Type I Type IIa TypeIIb • Oxidative capacity High Mod. High Low • Glycolytic capacity Low High Highest • Contractile speed Slow Fast Fast • Fatigue resistant High Moderate Low • Motor unit strength Low High High

38. Characteristics of Muscle Fiber Types • Characteristic ST FTa FTb • Fibers per motor neuron 10-180 300-800 300-800 • Motor neuron size Small Large Large • Nerve conduction velocity Slow Fast Fast • Contraction speed (ms) 110 50 50 • Type of myosin ATPase Slow Fast Fast • Sarcoplasmic Ret. Dev. Low High High

39. Motor Units A motor unit consists of a single motor neuron and all the muscle fibers it supplies

40. Neuro-muscular Interaction • Motor units give all-or-none responses. • For a unit to be recruited into activity, the motor nerve impulse must meet or exceed the threshold. • Threshold of excitation.

41. Neuro-muscular Interaction • When this occurs, all muscle fibers in the motor unit act maximally. • If the threshold is not met, no fibers in that unit act.

42. Neuro-muscular Interaction • More force is produced by activating more motor units, and thus more muscle fibers.

43. Neuro-muscular Interaction • In low-intensity activity, most muscle force is generated by ST fibers. • As the resistance increases, FTa fibers are recruited, and at even higher intensities, the FTb fibers are activated.

44. Ramping of Muscle Fibers

45. Neuro-muscular Interaction • The same pattern of recruitment is followed during events of long duration.

46. Muscle Action: • Muscles involved in a movement can be classified as: • agonists (prime movers) • antagonists (opponents or resistors) • synergists (assistants) • fixator, neutralizer, stabilizer

47. Muscle Action: • The three main types of muscle action are: • concentric, in which the muscle shortens; • static, in which the muscle acts but the joint angle is unchanged; • eccentric, in which the muscle lengthens.

48. Generation of Force • The number of motor units activated. • Force production can be increased by recruiting more motor units. • The type of motor units activated. • The size of the muscle.

49. Generation of Force: • The muscle’s initial length when activated. • Force production can be maximized if the muscle is stretched 20% prior to action. • At this point, the amount of energy stored and the number of linked actin-myosin cross-bridges are optimum.