1. Chapter 9 The Muscular System

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

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

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

6. Muscle Fiber (muscle cell) Cisternae of SR – enlarged portions Transverse tubules (T-tubules) – 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 – I band – on either side of Z line; actin filaments only H zone – 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 Synaptic vesicles – store neurotransmitter; most common – acetylcholine (ACh)

14. Electron Micrograph Neuromuscular Junction

15. 4 Proteins in Muscle Cells:

17. Troponin & Tropomyosin 4 proteins are found in muscle cells: actin, myosin, troponin & tropomyosin troponin – tropomyosin – appear as ribbons; cover the myosin cross-bridge binding sites in a relaxed muscle

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

19. Sliding Filament Theory (How Muscles Contract ) Linkages form b/t actin & myosin Muscle fiber relaxes when Ca²+ are transported back to S.R. The enzyme cholinesterase (or AChesterase) decomposes ACh

20. Sliding Filament Theory Relaxed muscle –

21. Sliding Filament Theory Ca²+ binds to troponin Tropomyosin slides out of the way Sarcomeres shorten & muscle contracts

22. Sliding Filament Theory

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

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

25. Energy for Muscle Contraction Creatine phosphate stores excess energy 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

26. 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.

27. 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 –

28. Aerobic vs. Anaerobic Respiration

29. 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

30. Strenuous exercise leads to O 2 deficiency & lactic acid buildup 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

31. Muscle cramp – Rigor mortis – takes up to 72 hrs. to occur; sarcolemma becomes more permeable to Ca+² & ATP levels insufficient Muscle Cramp

32. Myogram Pattern or graph of a muscle contraction A single contraction is called a muscle twitch 3 parts: Latent (lag) phase – Contraction Relaxation –

33. Patterns of Contraction a) Muscle Twitch – single contraction b) Staircase Effect

34. 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-

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

36. 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 –

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

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

39. Structural Differences of 3 Types of Muscle Skeletal MuscleSmooth MuscleCardiac Muscle Cells elongated w/multiple nuclei/cell Cells spindle- shaped w/1 nucleus/cell No T-tubulesT-tubules lg.; releases lg. amts. of Ca++; can contract longer (Ca channel blockers) Striated/voluntaryStriated/invol.

41. 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) Ca+² binds to calmodulin Ca+² binds to troponin Not affected by hormones Slower to contract but can maintain contraction longer Contracts & relaxes at a certain rate

42. 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)

43. Fast Twitch vs. Slow Twitch Muscle Fast TwitchSlow Twitch Contracts slowly, tires slowly (long distance) Fewer mitochondria Less myoglobinMore myoglobin Red muscle Composes smaller muscles (eyes, hands, etc.)

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

45. 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)

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