1. Chapter 9 The Muscular System

2. Skeletal Muscle Structure Tendon – connect muscle to bone Fascia – outermost covering; covers entire muscle & continuous w/tendon; separates muscle from adjacent muscles Aponeuroses- connect muscle to muscle

3. Skeletal Muscle Structure Coverings: Epimysium – covers entire muscle (under fascia) Perimysium – covers muscle bundle (fascicle) Endomysium – covers each fiber (cell) Sarcolemma – cell membrane

4. Skeletal Muscle Structure – Cont. Sarcoplasmic reticulum (SR) channels for transport Myofibrils – threads that compose muscle fibers; contain protein filaments: 1. actin – thin 2. myosin – thick Skeletal Muscle Structure

6. Muscle Fiber (muscle cell) Cisternae of SR – enlarged portions Transverse tubules (T-tubules) – important in muscle contraction Sarcoplasm – cytoplasm

7. Breakdown of Skeletal Muscle

8. Parts of a Sarcomere (functional unit of a muscle)

9. Parts of a Sarcomere Z lines – end points M line – middle I band – on either side of Z line; actin filaments only H zone – on either side of M line; myosin filaments only A band – overlapping actin & myosin filaments

10. Parts of a Sarcomere

11. Neuromuscular Junction – junction b/t motor neuron & muscle Motor neuron – carries impulse from brain or spinal cord to muscle Motor end plate – end of muscle fiber; many nuclei & mitochon- dria located here

12. Neuromuscular Junction Neurotransmitters (ntm) chemicals that help carry impulses Motor unit – 1 motor neuron & fibers that it stimulates Synaptic vesicles – store neurotransmitter; most common – acetylcholine (ACh)

14. Electron Micrograph Neuromuscular Junction

15. Neuromuscular Junction Animation

16. 4 Proteins in Muscle Cells:

18. Troponin & Tropomyosin 4 proteins are found in muscle cells: actin, myosin, troponin & tropomyosin troponin – appear as globules; provide a binding site for Ca+² tropomyosin – appear as ribbons; cover the myosin cross-bridge binding sites in a relaxed muscle

19. Sliding Filament Theory (How Muscles Contract) Muscle fiber stimulated by release of ACh from synaptic vesicles of neuron ACh causes impulse to travel to muscle cell membrane Transverse tubules (T-tubules) carry impulse deep into muscle fibers Sarcoplasmic reticulum releases Ca ions (Ca²+) Ca²+ bind to troponin, tropomyosin moves, exposing binding sites on actin filaments

20. Cross Bridge Animation cross bridge animation

21. Sliding Filament Theory (How Muscles Contract ) Linkages form b/t actin & myosin Actin filaments move inward, shortening the sarcomere Muscle fiber relaxes when Ca²+ are transported back to S.R. The enzyme cholinesterase (or AChesterase) decomposes ACh

22. Sliding Filament Theory Relaxed muscle – binding sites on actin are covered by tropomyosin

23. Sliding Filament Theory Ca²+ binds to troponin Tropomyosin slides out of the way Myosin binds to actin & pulls inward Sarcomeres shorten & muscle contracts

24. Sliding Filament Animation sliding filament animation

25. Sliding Filament Theory

26. Energy for Muscle Contraction ATP (adenosine triphosphate) provides the energy for muscle contraction When ATP is converted to ADP (adenosine diphosphate) by losing the last phosphate, energy is released.

27. Energy for Muscle Contraction Cells depend on cellular respiration of glucose to synthesize ATP An additional source is creatine phosphate

28. Energy for Muscle Contraction Creatine phosphate stores excess energy Can be used to convert ADP back into ATP Anaerobic respiration (in the absence of O 2 ) provides few ATP’s, while aerobic resp. (in the presence of O 2 ) provides many ATP’s

29. Creatine Phosphate High amts. of ATP - ATP is used to Low amts. of ATP – CP is used synthesize CP, which stores energy to resynthesize ATP. for later use.

30. Importance of Myoglobin l.a. carried by blood to liver; liver can convert l.a. to glucose, but requires ATP (ATP being used for muscle contraction) myoglobin – stores O 2 in muscle cells; gives muscle its red color

31. Aerobic vs. Anaerobic Respiration

32. Carried by blood to liver; liver can convert l.a. to glucose, but requires ATP (ATP being used for muscle contraction) Imp. b/c blood supply during muscle contr. may decrease As l.a. accumulates, O 2 debt occurs

33. Strenuous exercise leads to O 2 deficiency & lactic acid buildup ATP provides energy for muscle contraction Amt. of O 2 needed to convert accumulated l.a. to glucose & restore ATP levels = O 2 debt L.A. accumulation leads to muscle fatigue b/c pH of muscle cell is lowered & muscle cannot contract Oxygen Debt

34. Muscle cramp – fatigued muscle has lack of ATP needed to move Ca+² back into S.R.; cross bridges not broken Rigor mortis – takes up to 72 hrs. to occur; sarcolemma becomes more permeable to Ca+² & ATP levels insufficient Muscle Cramp

35. Myogram Pattern or graph of a muscle contraction A single contraction is called a muscle twitch 3 parts: Latent (lag) phase – brief pd. of delay b/t when the stimulus is applied & actual contraction occurs Contraction Relaxation – return to original state

36. Patterns of Contraction a) Muscle Twitch – single contraction b) Staircase Effect many stimuli closely spaced w/complete relaxation in b/t; each contraction generate incr. force

37. Patterns of Contraction c) Summation – when the 2 nd stimulus occurs during the relaxation pd. of 1 st contr.; the 2 nd contr. generates more force d) Tetany – when twitches fuse into 1 sustained contr.

38. Muscle Facts If a muscle is stimulated twice in quick succession, it may not respond the 2 nd time – called refractory period Threshold – the minimum stimulus needed to cause a contraction All-or-none – increasing the strength of the stimulation does NOT incr. the degree of contraction (a muscle contracts completely or not at all)

39. More Facts Incr. stimulation from motor neurons causes a greater # of motor units to contract & vice versa Called recruitment of motor units Incr. the rate of stimulation also incr. the degree of contraction Muscle tone – a sustained contraction caused by nerve impulses from s.c. to a small # of muscle fibers in the back, neck, etc.; maintains posture

40. Hypertrophy vs Atrophy Hypertrophy- with intense exercise where muscle exerts more than 75% of its max tension there is an increase in actin and myosin fibers and increase muscle fiber diameter. Inc diameter=inc. force of contraction. Atrophy- muscle diameter decreases with disuse as actin and myosin fibers diminish.

41. Origin & Insertion Origin – end of muscle that attaches to stationary bone Insertion – end of muscle that attaches to moving bone During contr., insertion is pulled toward origin

42. Muscle Functions in Groups Prime mover – responsible for most of the movement (ex.- biceps) Synergist – aids the prime mover Antagonist – resists the prime mover & causes movement in the opposite direction (ex. - triceps)

43. Structural Differences of 3 Types of Muscle Skeletal MuscleSmooth MuscleCardiac Muscle Cells elongated w/multiple nuclei/cell Cells spindle- shaped w/1 nucleus/cell Cells branching w/1 nucleus/cell T-tubules presentNo T-tubulesT-tubules lg.; releases lg. amts. of Ca++; can contract longer (Ca channel blockers) Striated/voluntaryNon-striated/invol.Striated/invol.

45. Functional Differences of 3 Types of Muscle Skeletal MuscleSmooth MuscleCardiac Muscle Needs nerve impulse for contraction Displays rhythmicity & cells stimulates each other (as in peristalsis) Displays rhythmicity & self-excitation Ca+² binds to troponinCa+² binds to calmodulin Ca+² binds to troponin Not affected by hormones Hormones may affect contraction Hormones may affect rate of contr. Contracts & relaxes rapidly Slower to contract but can maintain contraction longer Contracts & relaxes at a certain rate

46. Functional Differences - Continued Skeletal MuscleSmooth MuscleCardiac Muscle Not affected by stretching Stretching of fibers may stimulate contr. (ex.-stomach) Remains in a refractory pd. until contraction ends (tetany won’t occur)

47. Fast vs Slow Twitch Fibers Fast vs Slow Twitch Video

48. Fast Twitch vs. Slow Twitch Muscle Fast TwitchSlow Twitch Contracts quickly, tires easily (sprinter) Contracts slowly, tires slowly (long distance) Fewer mitochondriaMore mitochondria Less myoglobinMore myoglobin White muscleRed muscle Composes smaller muscles (eyes, hands, etc.) Composes lg. muscles (legs, back, etc.)

49. Levers Parts of a lever: wt., force, pivot 3 types of levers: 1 st class – W-P-F (seesaw/scissors) 2 nd class – P-W-F (wheelbarrow) 3 rd class – W-F-P (forceps)

50. Bones & Muscles as Levers Forearm bends – 3 rd class lever (biceps attaches at a pt. on the radius below the elbow joint) Forearm straightens - 1 st class lever ((triceps attaches at a pt. on the ulna above the elbow joint)

51. Bones & Muscles as Levers Standing on tip-toe – 2 nd class lever (P-W-F)