Chapter 6

1. Chapter 6 The Muscular System

2. The essential function of a muscle is to shorten or contract • As a result of this ability, muscles are responsible for almost all body movement and can be viewed as the “machines of the body”

3. Overview of Muscle Tissues

4. Muscle Types - Three • Skeletal • Cardiac • Smooth

5. The 3 Types of Muscle Tissue differ in: • Cell structure • Body location • How they are stimulated to contract

6. The three types of muscle tissue are similar because: • All muscle cells are elongated – called muscle fibers • The ability of muscle to shorten or contract depends on 2 types of myofilaments (part of the cytoskeleton)

7. Skeletal Muscle • Fibers are packaged into skeletal muscles that attach to the skeleton • Cigar-shaped • Multinucleate (many nuclei) • Largest of the muscle fibers

8. Striated muscle (appear striped) • Voluntary muscle (conscious control) • Form smoother contours of the body

9. Key words to think of for skeletal muscle: • Skeletal, striated, voluntary

10. Skeletal muscles are very fragile, but they are capable of exerting tremendous power. • They are able to do this because: thousands of fibers are bundled together with connective tissue – these bundles are then bundled together

11. Tendons • Attach muscle to bone

12. Figure 09.02

13. Functions of the tendons • Anchor muscles • Provide durability and conserve space • Crossover bony projections

14. Smooth Muscle • No striations • Involuntary • Found in the walls of hollow digestive organs • Propels substances along a definite path

15. Spindle shaped • Single nucleus • Arranged in sheets or layers • Muscle contraction is slow and sustained

16. Key words: • Visceral, non-striated, involuntary

17. Cardiac Muscle • Found only the heart • Striated and involuntary

18. Key Words: • Cardiac • Striated • involuntary

19. Muscle Functions • Muscles play four important roles in the body.

20. 1. Produce movement • Moves the body

21. 2. Maintain posture • Allow you to remain in an erect or seated posture despite gravity

22. 3. Stabilize Joints • Muscle tendons are extremely important in reinforcing and stabilizing joints

23. 4. Generating Heat • Heat is a by product of muscle activity • ATP used as power – ¾ escapes as heat

24. Microscopic Anatomy of Skeletal Muscles • Skeletal muscle contains both actin and mysosin filaments • The overlapping pattern of thick and thin filaments is responsible for the light and dark bands seen in skeletal striated muscle

25. The thick filaments are made up of a protein called myosin • The thin filaments are made of a protein called actin. • Sarcomere: contractile unit

26. Skeletal Muscle Activity

27. The 2 special functional properties of muscles: • Irritability – ability to receive and respond to a stimuli • Contractility – ability to shorten with adequate stimuli • Skeletal muscles must be stimulated by nerve impulses to contract.

28. Motor Unit • One neuron (nerve cell) and all the skeletal muscles it stimulates

29. Figure 09.09

30. How a muscle contracts • A nerve impulse reaches the end of the nerve a neurotransmitter is released. • The neurotransmitter that stimulates skeletal muscle is acetylcholine (Ach) • When enough acetylcholine is released, sodium ions (Na+) will rush into the muscle. • This rush of ions creates an electrical current known as the action potential. • The action potential travels over the entire muscle causing it to contract.

31. The events that return a muscle to its resting state: • Diffusion of K+ (potassium) out of the cell • Activation of the Na+/K+ pump

33. The Sliding Filament Theory • Muscle fibers contract when the sarcomere shortens. • The sarcomere shortens when the actin fibers slide past the myosin filaments • Myosin moves the actin.

34. The sliding filament theory refers to the movement of actin in relation to myosin. • ATP supplies the energy for muscle contraction. • Myosin filaments do all the work. The actin filaments just sit there.

37. Figure 09.04

38. Myosin filaments breakdown ATP and have crossbridges that pull the actin filaments toward the center of the sarcomere.

39. Contraction of Skeletal Muscle as a whole

40. Figure 09.06

41. Graded Responses • Different degrees of shortening • Different numbers of muscles contract

42. Graded muscle contractions can be produced in two ways: • By changing the speed of muscle stimulation • By changing the number of muscle cells being stimulated

43. Providing Energy for Muscle Contraction

44. 1. Direct phosphorylation of ADP by creatine phosphate (CP) • CP gives a phosphate to ADP to make ATP • ATP is regenerated in a fraction of a second • CP supplied energy used in 20 seconds

45. 2. Aerobic Respiration – ATP is made by aerobic respiration • 1 glucose – 36 ATP • Fairly slow – needs continuous supply of oxygen Adenosine Triphosphate

46. 3. Anaerobic Respiration and Lactic Acid Formation • No oxygen • 2 ATP per glucose • Lactic acid is made and builds up in muscles • 5X faster than aerobic • 30-40 seconds of strenuous exercise • Problems: needs lots of glucose • Small amount of ATP produced per glucose • Lactic acid

47. 3. Anaerobic Respiration and Lactic Acid Formation • No oxygen • 2 ATP per glucose • Lactic acid is made and builds up in muscles • 5X faster than aerobic • 30-40 seconds of strenuous exercise • Problems: needs lots of glucose • Small amount of ATP produced per glucose • Lactic acid

48. Muscle Fatigue and Oxygen Debt

49. Muscle Fatigue • Occurs when muscles are exercised strenuously

50. Fatigued • When a muscle is unable to contract even though it is being stimulated