Chapter 9 The Muscular System

1. Chapter 9The 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 Skeletal Muscle Structure – Cont. • Sarcoplasmic reticulum (SR) channels for transport • Myofibrils – threads that compose muscle fibers; contain protein filaments: 1. actin – 2. myosin –

5. 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 O2) provides few ATP’s, while aerobicresp. (in the presence of O2) 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. Aerobic vs. Anaerobic Respiration 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, O2 debt occurs

30. Oxygen Debt • Strenuous exercise leads to O2 deficiency & lactic acid buildup • Amt. of O2 needed to convert accumulated l.a. to glucose & restore ATP levels = O2 debt • L.A. accumulation leads to muscle fatigue b/c pH of muscle cell is lowered & muscle cannot contract

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

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) MuscleTwitch – single contraction • b) Staircase Effect

34. Patterns of Contraction • c) Summation – when the 2nd stimulus occurs during the relaxation pd. of 1st contr.; the 2nd contr. generates more force • d) Tetany-

35. Muscle Facts • If a muscle is stimulated twice in quick succession, it may not respond the 2nd 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

41. Functional Differences of 3 Types of Muscle

42. Functional Differences - Continued

43. Fast Twitch vs. Slow Twitch Muscle

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

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

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