PowerLecture: Chapter 6

1. PowerLecture:Chapter 6 The Muscular System

2. Learning Objectives • Explain the structure of muscles, from the molecular level to the organ systems level. • Explain how biochemical events occur in muscle contractions and how antagonistic muscle action refines movements. • Explain the differences in stimulation required for each type of muscle and how each responds. • Demonstrate how muscle disorders impact the function of both the muscular and skeletal systems.

3. Impacts/Issues Pumping Up Muscles

4. Pumping Up Muscles • Can you bulk up your muscles by using a pill and do so safely? • Androstenedione and THG are available as supplements but are really steroid-like drugs unapproved by the FDA. • Another unapproved performance enhancer is creatine, a substance normally produced by the body during muscle activity.

5. Pumping Up Muscles • The intricate movements of the human body are the result of interactions between the skeleton and muscle.

6. How Would You Vote? To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main menu. • Dietary supplements are largely unregulated. Should they be subject to more stringent testing for effectiveness and safety? • a. Yes, or companies could make any claim about their product. • b. No, so long as the extract does no harm, let the buyer decide what to buy.

7. Section 1 The Body’s Three Kinds of Muscle

8. The Body’s Three Kinds of Muscle • The three kinds of muscle are built and function in different ways. • Skeletal muscle, composed of long thin cells called muscle “fibers,” allows the body to move. • Smooth muscle is found in the walls of hollow organs and tubes; the cells are smaller than those of skeletal muscle and are not striated. • The heart is the only place where cardiac muscle is found.

9. One skeletal muscle fiber Skeletal muscle Fig. 6.1, p.104

10. Smooth muscle fibers Smooth muscle Fig. 6.1, p.104

11. Cardiac muscle fibers Cardiac muscle Fig. 6.1, p.104

12. The Body’s Three Kinds of Muscle • Cardiac muscle and smooth muscle are considered involuntary muscles because we cannot consciously control their contraction; skeletal muscles are voluntary muscles. • Skeletal muscle comprises the body’s muscular system.

13. Fig. 6.2, p.105 © 2001 Brooks/Cole . Thomson ©2005 Brooks/Cole . Thomson © 2007 - Thomson Higher Education TRICEPS BRACHII BICEPS BRACHII PECTORALIS MAJOR DELTOID TRAPIZIUS SERRATUS ANTERIOR EXTERNAL OBLIQUE LATISSIMUS DORSI RECTUS ABDOMINUS GLUTEUS MAXIMUS ADDUCTOR LONGUS BICEPS FEMORIS SARTORIUS QUADRICEPS FEMORIS GASTROCNEMIUS TIBIALIS ANTERIOR

14. flexor digitorum superficialis Fig. 6.20a, p.118

15. zygomaticus major Fig. 6.20b, p.118

16. Section 2 The Structure and Function of Skeletal Muscles

17. The Structure and Function of Skeletal Muscles • A skeletal muscle is built of bundled muscle cells. • Inside each cell are threadlike myofibrils, which are critical to muscle contraction. • The cells are bundled together with connective tissue that extends past the muscle to form tendons, which attach the muscle to bones.

18. Fig. 6.4, p.106 muscle tendon (attached to bone) fluid tendon sheath bone

19. Fig. 6.3, p.106 muscle’s outer sheath (connective tissue) two bundles of muscle cells (each has its own connective tissue sheath) one muscle cell one myofibril

20. The Structure and Function of Skeletal Muscles • Bones and skeletal muscles work like a system of levers. • The human body’s skeletal muscles number more than 600. • The origin end of each muscle is designated as being attached to the bone that moves relatively little; whereas the insertion is attached to the bone that moves the most. • Because most muscle attachments are located close to joints, only a small contraction is needed to produce considerable movement of some body parts (leverage advantage).

21. The Structure and Function of Skeletal Muscles • Many muscles are arranged as pairs or in groups. • Many muscles are arranged as pairs or grouped for related function. • Some work antagonistically (in opposition) so that one reverses the action of the other. • Others work synergistically, the contraction of one stabilizes the contraction of another. • Reciprocal innervation dictates that only one muscle of an antagonistic pair (e.g. biceps and triceps) can be stimulated at a time.

22. Fig. 6.5, p.107 triceps relaxes origin triceps contracts, pulls the forelimb down biceps contracts at the same time, and pulls forelimb up at the same time, biceps relaxes insertion

23. The Structure and Function of Skeletal Muscles • “Fast” and “slow” muscle. • Humans have two general types of skeletal muscles: • “Slow” muscle is red in color due to myoglobin and blood capillaries; its contractions are slower but more sustained. • “Fast” or “white” muscle cells contain fewer mitochondria and less myoglobin but can contract rapidly and powerfully for short periods.

24. Fig. 6.6, p.107

25. The Structure and Function of Skeletal Muscles • When athletes train, one goal is to increase the relative size and contractile strength of fast (sprinters) and slow (distance swimmers) muscle fibers. Figure 6.6b

26. Section 3 How Muscles Contract

27. How Muscles Contract • A muscle contracts when its cells shorten. • Muscles are divided into contractile units called sarcomeres. • Each muscle cell contains myofibrils composed of thin (actin) and thick (myosin) filaments. • Each actin filament is actually two beaded strands of protein twisted together. • Each myosin filament is a protein with a double head (projecting outward) and a long tail (which is bound together with others). • The arrangement of actin and myosin filaments gives skeletal muscles their characteristic striped appearance.

28. Fig. 6.8, p.108 one actin molecule part of a thin filament a Arrangement of actin molecules in the thin filaments part of a myosin molecule part of a thick filament b Arrangement of myosin molecules in the thick filaments

29. Fig. 6.7a, p.108 One myofibril inside cell: a. Skeletal muscle cell, longitudinal section. All bands of its myofibrils are in register and give the cell a striped appearance.

30. sarcomere sarcomere Z band H zone Z band Z band b. Sarcomeres. Many thick and thin filaments overlap in an A band. Only thick filaments extend across the H zone. Only thin filaments extend across I bands to the Z bands. I band A band I band Fig. 6.7b, p.108

31. How Muscles Contract • Muscle cells shorten when actin filaments slide over myosin. • Within each sarcomere there are two sets of actin filaments, which are attached on opposite sides of the sarcomere; myosin filaments lie suspended between the actin filaments.

32. Fig. 6.9, p.109 actin myosin actin a Sarcomere when muscle cell is relaxed b Same sarcomere, contracted

33. myosin actin actin p.116

34. How Muscles Contract • During contraction, the myosin filaments physically slide along and pull the two sets of actin filaments toward each other at the center of the sarcomere; this is called the sliding-filament model of contraction. • When a myosin head is energized, it forms cross-bridges with an adjacent actin filament and tilts in a power stroke toward the sarcomere’s center. • Energy from ATP drives the power stroke as the heads pull the actin filaments along. • After the power stroke the myosin heads detach and prepare for another attachment (power stroke).

35. Fig. 6.9cd, p. 109 myosin head one of many myosin binding sites on actin cross bridge cross bridge

36. Fig. 6.9ef, p. 109

37. ATP ATP Fig. 6.9g, p. 109

38. How Muscles Contract • When a person dies, ATP production stops, myosin heads become stuck to actin, and rigor mortis sets in, making the body stiff.

39. Section 4 How the Nervous System Controls Muscle Contraction

40. How the Nervous System Controls Muscle Contraction • Calcium ions are the key to contraction. • Skeletal muscles contract in response to signals from motor neurons of the nervous system. • Signals arrive at the T tubules of the sarcoplasmic reticulum (SR), which wraps around the myofibrils. • The SR responds by releasing stored calcium ions; calcium binds to the protein troponin, changing the conformation of actin and allowing myosin cross-bridges to form. • Another protein, tropomyosin, is also associated with actin filaments.

41. How the Nervous System Controls Muscle Contraction • When nervous stimulation stops, calcium ions are actively taken up by the sarcoplasmic reticulum and the changes in filament conformation are reversed; the muscle relaxes.

42. Fig. 6.10, p. 110 section from spinal cord © 2007 Thomson Higher Education motor neuron a Signals from the nervous system Endings of motor neuron b sarcoplasmic reticulum(calcium in storage) T tubule plasma membrane of skeletal muscle fiber section from a skeletal muscle one of the myofibrils inside the muscle fiber part of one muscle cell Signals travel along muscle cell’s plasma membrane to sarcoplasmic reticulum around myofibrils. c Z line Z line Signals trigger the release of calcium ions from sarcoplasmic reticulum threading among the myofibrils. d

43. troponin a Actin molecule myosin binding site blocked b Cross-section of (a). Red dots are calcium ions bound to troponin (green). c Calcium ions flow in; troponin binds additional calcium. d Troponin changes shape,moving away from the myosin binding site. myosinhead eThe binding site is now exposed; actin can bind the myosin head. myosinhead cross-bridge f Cross-bridge forms between actin and myosin. Fig. 6.11, p. 111

44. Fig. 6.11a.c, p.111 troponin a Actin molecule myosin binding site blocked b Cross-section of (a). Red dots are calcium ions bound to troponin (green). c Calcium ions flow in; troponin binds additional calcium.

45. Fig. 6.11d.f, p.111 myosinhead dTroponin changes shape,moving away from the myosin binding site. e The binding site is now exposed; actin can bind the myosin head. myosinhead fCross-bridge forms between actin and myosin.

46. How the Nervous System Controls Muscle Contraction • Neurons act on muscle cells at neuromuscular junctions. • At neuromuscular junctions, impulses from the branched endings (axons) of motor neurons pass to the muscle cell membranes. • Between the axons and the muscle cell is a gap called a synapse. • Signals are transmitted across the gap by a neurotransmitter called acetylcholine (ACh). • When the neuron is stimulated, calcium channels open to allow calcium ions to flow inward, causing a release of acetylcholine into the synapse.

47. Vesicles containing ACh molecules Axon ending of motor neuron Synapse Muscle cell Muscle cell receptor for ACh Fig. 6.12, p.111

48. Section 5 How Muscle Cells Get Energy

49. How Muscle Cells Get Energy • ATP supplies the energy for muscle contraction. • Initiation of muscle contraction requires much ATP; this will initially be provided by creatinephosphate, which gives up a phosphate to ADP to make ATP. • Cellular respiration provides most of the ATP needed for muscle contraction after this, even during the first 5-10 minutes of moderate exercise.

50. How Muscle Cells Get Energy • During prolonged muscle action, glycolysis alone produces low amounts of ATP; lactic acid is also produced, which hinders further contraction. • Muscle fatigue is due to the oxygen debt that results when muscles use more ATP than cellular respiration can deliver.