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Chapter 6

Chapter 6. The Muscular System. 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”. Overview of Muscle Tissues. Muscle Types - Three. Skeletal

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Chapter 6

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  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

  32. 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.

  33. 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.

  34. Figure 09.04

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

  36. Contraction of Skeletal Muscle as a whole

  37. Figure 09.06

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

  39. 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

  40. Providing Energy for Muscle Contraction

  41. 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

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

  43. 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

  44. 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

  45. Muscle Fatigue and Oxygen Debt

  46. Muscle Fatigue • Occurs when muscles are exercised strenuously

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

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