Chapter 8: The Muscular System

1. Chapter 8: The Muscular System

2. I. Introduction Muscular tissue enables the body and its parts to move: • Contraction-the shortening of muscle fibers; causes movement • Muscle cells shorten by converting chemical energy from nutrient molecules (food) to mechanical energy • As muscle fibers contract they pull on bone to produce movement

3. II. Muscle Tissue • Types of muscle tissue • Skeletal muscle-also called striated or voluntary muscle • Attaches to bone; are threadlike, cylindrical fibers • Appear in bundles; have crosswise stripes (striations) and multiple nuclei • Can be controlled voluntarily

4. http://clcpages.clcillinois.edu/home/bio567/pages/newtissues/Skeletal%20muscle%2001a.jpghttp://clcpages.clcillinois.edu/home/bio567/pages/newtissues/Skeletal%20muscle%2001a.jpg

5. 2. Cardiac muscle makes up most of the heart a. Cells are also cylindrical, but branch and recombine b. Cells have dark bands called intercalated disks and are multinucleate c. The interconnectedness allows the heart to contract as a unit.

6. http://www.cytochemistry.net/microanatomy/muscle/muscle12.jpghttp://www.cytochemistry.net/microanatomy/muscle/muscle12.jpg

7. 3. Smooth or nonstriated muscle also called involuntary or visceral • No striations, single nucleus, cells taper at each end • No voluntary control of contractions • Found in the walls of hollow, visceral structures

8. http://missinglink.ucsf.edu/lm/IDS_101_histo_resource/images/351Blabeled_copy.jpghttp://missinglink.ucsf.edu/lm/IDS_101_histo_resource/images/351Blabeled_copy.jpg

9. B. Function-all muscle cells specialize in contraction http://graphics8.nytimes.com/images/2007/08/01/health/adam/19917.jpg

10. III. Structure of Skeletal Muscle A. Gross anatomy • Each skeletal muscle is an organ composed mainly of skeletal muscle cells and connective tissue. 2. Most skeletal muscles extend from one bone across a joint to another bone. 3. Parts of a skeletal muscle (figure 8-2) • origin-the muscle’s attachment to the more stationary bone • insertion-the point of attachment to the bone that moves when the muscle contracts • Body (belly)-the rest of the muscle; the main part.

11. Origin http://graphics8.nytimes.com/images/2007/08/01/health/adam/19917.jpg Body Insertion

12. 4. Muscles attach to bone by tendons, strong cords of dense fibrous connective tissue • Some are enclosed in synovial lined tubes called tendon sheaths and are lubricated by synovial fluid. 5. Bursae-lie between some tendons and the bones beneath them. Small sacs lined with synovial membrane which secretes synovial fluid that fills the sac.

13. http://www.arc.org.uk/arthinfo/medpubs/6524/images/6524_1.gifhttp://www.arc.org.uk/arthinfo/medpubs/6524/images/6524_1.gif

14. B. Microscopic structure • Skeletal muscle cells are called fibers-they are grouped together in bundles http://www.web-books.com/eLibrary/Medicine/Physiology/Muscular/muscle_structure.jpg

15. 2. Fibers contain: a. Thick myofilaments-contain the protein myosin b. Thin myofilaments-contain the protein actin http://www.exrx.net/Images/ActinMyosin.gif

16. 3. The basic functional unit of muscle is the sarcomere. Sarcomeres are separated from each other by dark bands called z-lines 4. The sliding filament model explains how contraction takes place. a. Thick & thin myofilaments slide past each other, shortening the sarcomere and hence, the entire fiber b. Contraction requires calcium and energy rich ATP molecules

17. http://www.carolguze.com/images/cellorganelles/actin-myosin.jpghttp://www.carolguze.com/images/cellorganelles/actin-myosin.jpg

18. IV. Functions of Skeletal Muscle A. Movement 1. As a muscle contracts it pulls the insertion bone toward the origin bone-movement occurs at the joint in between. 2. Groups of muscles usually contract to produce a single movement a. Prime mover-the muscle whose contraction is mainly responsible for a given movement b . Synergist-helps the prime mover c. Antagonist- actions oppose the action of the prime mover.

19. B. Posture • A specialized type of muscle contraction called tonic contraction enables the body to maintain body position. 2. In tonic contraction only a few of a muscle’s fibers shorten at a time. They hold muscles in position 3. Tonic contractions produce no movement of body parts. 4. Tonic contractions maintain muscle tone called posture. a. Good posture –when body parts are held in a position that favors best function: ↓strain on muscles, tendons, ligaments & bones. b. Poor posture can cause fatigue and even deformity.

20. C. Heat Production • The body must maintain a relatively constant body temperature for survival. • Fever- elevated body temperature b. hypothermia-reduced body temperature 2. Muscle fiber contraction produces most of the heat required to maintain normal body temperature.

21. D. Fatigue • Is caused by repeated muscle stimulation w/o adequate rest • Strength of contraction decreases. If process continues contraction strength continues to ↓ and may stop. • Repeated muscular contraction depletes stored ATP & O2 and exceeds the ability of the blood supply to replenish. • Contraction in the absence of O2 produces lactic acid-leads to muscle soreness. • Oxygen debt-the continues increased metabolism that must occur in a cell to remove the excess lactic acid that accumulates during exercise.

22. V. Role of other Body Systems in Movement • Muscular function depends on the healthy functioning of other parts of the body. 1. Bones and joints must function with them. 2. Respiratory & circulatory function effect muscle function also. 3. Nervous system functioning is very important.

23. B. Examples of how pathologic conditions in other body organ systems can drastically affect movement 1. The muscles may be perfectly normal, but… 2. Nervous system disorders can shut off impulses to muscles causing paralysis. 3. Examples: multiple sclerosis, brain or spinal cord injury, stroke.

24. VI. The Motor Unit A. Stimulation of a muscle by a nerve impulse is required before a muscle can shorten and produce movement. B. A motor neuron is a specialized nerve that transmits an impulse to a muscle, causing contraction. It releases acetylcholine which causes the sarcoplasmic reticulum to release Ca2+ which triggers the actin/myosin slide.

25. C. A neuromuscular junction is the point of contact between a nerve ending and the muscle fiber it innervates. D. A motor unit is a single motor neuron with the muscle fibers it innervates.

26. VII. Muscle Stimulus A. A muscle will only contract if a stimulus reaches a certain level of intensity. A threshold stimulus is the minimal level of stimulus intensity required to cause a muscle fiber to contract. B. Once stimulated by a threshold stimulus a muscle fiber will contract completely-this is called “all or none” response.

27. C. A muscle has many muscle fibers that are controlled by different motor units with different threshold levels. D. This allows a muscle to have contractions of varying force.

28. VIII. Types of Skeletal Muscle Contraction • Twitch contraction-single contraction of muscle fibers by a single threshold stimulus-in lab only. B. Tetanic contraction-series of stimuli bombard the muscle in rapid succession; contractions run together.

29. C. Isotonic contraction-produces movement at a joint, the muscle changes length; most body movements are of this type. D. Isometric contraction-tension within the muscle increases but there is no movement & entire muscle does not shorten.

30. IX. Effects of Exercise on Skeletal Muscles A. Regular, appropriate exercise results in: 1. Improved muscle tone 2. Improved posture 3. More efficient heart & lung functioning 4. Reduces fatigue

31. B. Muscles undergo changes related to the amount of work they normally do 1. Atrophy- muscles shrink in mass due to disuse 2. Hypertrophy-muscles increase in size with regular exercise.

32. C. Strength training is exercise involving contraction against heavy resistance. 1. Increases the# of myofilaments in each muscle fiber; the total mass of muscle increases. 2. The # of muscle fibers does not increase. D. Endurance training is exercise that increases a muscle’s ability to sustain moderate activity over time. It is sometimes called aerobic training. 1. There is usually no increase in muscle mass, but… 2. There is an increase in the # of blood vessels to the muscle.

33. X. Skeletal Muscle Groups (Table 8-1) A. Muscles of the head and neck 1. Facial muscles a. Orbicularis oculi b. Orbicularis oris c. Zygomaticus 2. Muscles of mastication (chewing) a. Masseter b. Temporal 3. Sternocleidomastoid flexes head 4. trapezius -elevates shoulders and extends head

34. B. Muscles that move the upper extremities • Pectoralis major-flexes upper arm • Latissumus dorsi-extends upper arm • Deltoid -abducts upper arm • Biceps brachii-flexes forearm • Triceps brachii-extends forearm

35. C. Muscles of the trunk 1. Abdominal muscles • Rectus abdominus • External oblique • Internal oblique • Transverse abdominus 2. Respiratory muscles • Intercostal muscles • diaphragm

36. D. Muscles that move the lower extremities • iliopsoas-flexes thigh • Gluteus maximus-extends thigh • Adductor muscles-adducts thighs • Hamstring muscles-flexes lower leg • Semimembranosus • Semitendonosus • Biceps femoris

37. 5. Quadriceps femoris group-extends lower leg a. rectus femoris b. vastus muscles 6. Tibialis anterior-dorsiflexes foot 7. gastrocnemius- plantar flexes foot 8. Peroneus group-plantar flexes foot

38. E. Movements produced by skeletal muscle contraction • flexion-decreases the angle between 2 bones at a joint; bending • Extension-increases the angle between bones; straightening. • Abduction-moves a body part away from midline. • Adduction-moves a body part toward midline • Rotation-movement around an axis.

39. 6. Hand positions that result from rotation of the forearm: • supination-palms toward anterior position • Pronation-palms face posteriorally 7. Foot movements a. dorsiflextion-elevation of top of foot b. plantar flexion-”standing on toes” bottom of foot downward

40. XI. Major Muscular Disorders A. Myopathies –muscle disorders that disrupt the normal movement of the body; can be mild or life-threatening

41. B. Muscle injury • Strain-injury from overexertion or trauma involving stretching or tearing of muscle fibers. • myalgia-muscle pain b. inflammation of muscle: myositis or of muscle and tendons fibromyositis http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/19618.jpg

42. http://www.boogiewoogieindia.com/wp-content/uploads/2009/01/ankle-sprain.jpghttp://www.boogiewoogieindia.com/wp-content/uploads/2009/01/ankle-sprain.jpg c. sprain-injury near a joint involving ligament damage

43. 2. cramps-painful muscle spasms http://1.bp.blogspot.com/_Jl0wRt7PfiM/SrszFQOyHRI/AAAAAAAAAe4/V5VwFQ8Iroo/s400/Muscle_Cramp.jpg

44. 3. crush injuries-severe injury; release of muscle fiber contents into blood: myoglobin can cause kidney failure 4. stress induced muscle tension causes: myalgia, “tension headaches”, stiff neck, etc.

45. C. Muscle infections • Several types of bacteria, viruses, & parasites can infect muscles. • Poliomyelitis-a viral infection of the motor nerves. Can be asymptomatic or deadly. Causes paralysis.

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47. D. Muscular Dystrophy 1. A group of genetic disorders characterized by muscle atrophy. 2. Duchenne M.D. is the most common type. • Muscles atrophy and are replaced w/ fat & fibrous tissue; rapid progression of weakness

48. E. Myasthenia Gravis An autoimmune disease; muscle cells are attacked at the neuromuscular junction. Nerve impulses are unable to stimulate muscles. Causes weakness, fatigue; begins with muscles of face and can progress to death from respiratory failure.

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50. Adapted from The Human Body in Health and Disease. Thibodeau, Gary A. & Patton, Kevin T. Mosby, 2005