The Muscular System

1. The Muscular System

2. The Muscular System • Muscles are responsible for movement through contraction • Three basic muscle types are found in the body • Skeletal muscle • Cardiac muscle • Smooth muscle • skeletal & smooth muscle cells are elongated & are called muscle fibers - muscle terminology – prefixes myo- and mys- (“muscle”) & sarco- (“flesh”)

3. Comparison of Skeletal, Cardiac, and Smooth Muscles Table 6.1 (1 of 2)

4. Comparison of Skeletal, Cardiac, and Smooth Muscles Table 6.1 (2 of 2)

5. 1. Skeletal Muscle Characteristics • contain multinucleate cells • Striated - having visible bands/stripes • under voluntary or conscious control

6. a. Connective Tissue Wrappings of Skeletal Muscle • Endomysium - covers each muscle fiber • Fascicle - bundle of muscle fibers • Perimysium - covers each fascicle • Epimysium - covers the entire muscle • epimysium blends into either a cordlike tendon which is dense/fibrous connective tissue or a sheetlike aponeuroses which attach muscles indirectly

7. Connective Tissue Wrappings of Skeletal Muscle Figure 6.1

9. 2. Smooth Muscle Characteristics • no striations or stripes • under involuntary control • found mainly in the walls of hollow organs such as the stomach, bladder & respiratory passages • cells are spindle shaped

10. Smooth Muscle Characteristics Figure 6.2a

11. 3. Cardiac Muscle Characteristics • Found only in the heart • Striated - having bands/stripes • under involuntary control • muscle fibers are branching cells joined by junctions called intercalated discs

12. Cardiac Muscle Characteristics Figure 6.2b

13. B. Skeletal Muscle Functions • Produce movement - skeletal muscles responsible for locomotion - smooth muscle of vessels & cardiac muscle of the heart work together to circulate blood & maintain blood pressure - smooth muscles of hollow organs force fluids & other substances (food, a baby) through body channels

14. Maintain Posture - skeletal muscles working continuously to maintain a erect or seated posture despite the downward pull of gravity • Stabilize Joints - skeletal muscles stabilize & reinforce joints that have poorly fitting articular surfaces 4. Generating Heat - heat is a byproduct of muscle contraction - ¾ of the energy from ATP escapes as heat - necessary for homeostasis in maintaining body temp.

15. II. Microscopic Anatomy of Skeletal Muscle • Sarcolemma - specialized plasma membrane • Myofibrils - long organelles inside the muscle cell 1. Sarcomere - contractile units of a myofibril 2. Sarcomeres are made of myofilaments (threadlike protein) a. Actin - thin filaments b. Myosin- thick filaments

16. Microscopic Anatomy of Skeletal Muscle Figure 6.3a

17. The thick filaments or myosin produce the dark A band which is where they overlap with the thin filaments or actin. The thin filaments or actin produce the light I band which is where they do not overlap the myosin. The A bands are bisected by the H zone which is where there is no overlap between the actin and myosin filaments The Z lines separate the individual sarcomeres

18. Microscopic Anatomy of Skeletal Muscle Figure 6.3b

19. Microscopic Anatomy of Skeletal Muscle Figure 6.3c

20. Microscopic Anatomy of Skeletal Muscle C. Sarcoplasmic Reticulum - specialized smooth endoplasmic reticulum - surrounds each myofibril - stores & releases calcium (needed for muscle contraction)

21. Microscopic Anatomy of Skeletal Muscle Figure 6.3d

22. 1. The Nerve Stimulus and Action Potential • to contract, skeletal muscle cells must be stimulated by nerve impulses • Motor unit - one neuron & all the skeletal muscle cells it stimulates • Neuromuscular junction - where a neuron meets a muscle cell • Synaptic cleft - gap between a neuron & muscle cell

23. The Nerve Stimulus and Action Potential Figure 6.4a

24. The Nerve Stimulus and Action Potential Figure 6.4b

25. The Nerve Stimulus and Action Potential Figure 6.5a

26. The Nerve Stimulus and Action Potential Figure 6.5b

27. a neurotransmitter called acetylcholine or ACh is released due to a nerve impulse • Sarcolemma becomes more permeable to sodium ions Na+ • more Na+ enters the cell than K+ leaves the cell creating an action potential resulting in a muscle contraction • sodium-potassium pump (an active transport mechanism) moves Na+ & K+ ions back to their initial positions

28. Transmission of Nerve Impulse to Muscle Figure 6.5c

29. Transmission of Nerve Impulse to Muscle Figure 6.6

30. 2. The Sliding Filament Theory of Muscle Contraction • the action potential stimulates the sarcolemma to release Ca++ • Ca++ ions trigger the binding of myosin to actin initiating filament sliding causing the muscle to shorten

31. The Sliding Filament Theory of Muscle Contraction Figure 6.7a–b

32. The Sliding Filament Theory Figure 6.8a

33. The Sliding Filament Theory Figure 6.8b

34. The Sliding Filament Theory Figure 6.8c

35. B. Contraction of Skeletal Muscle • Graded Responses - muscle fiber/cell contraction is “all-or-none” & does not apply to the entire muscle which react to stimuli with graded responses or different degrees of shortening

36. Muscle Response to Increasingly Rapid Stimulation - muscle twitch - single brief contraction/not normal - tetanus- summing of contractions/one contraction is immediately followed by another

37. Types of Graded Responses Figure 6.9a

38. Types of Graded Responses Figure 6.9b

39. Types of Graded Responses Figure 6.9c

40. Types of Graded Responses Figure 6.9d

41. b. Muscle Response to Strong Stimuli • muscle contraction force depends on # of fibers stimulated – can be a slight or vigorous contraction

42. 2. Providing Energy for Muscle Contraction • ATP is needed to power contraction & only 4-6 seconds worth of ATP is stored in the muscles, after which time other pathways produce ATP

43. Energy for Muscle Contraction • Creatine Phosphate (CP) – high energy molecule - CP interacts with ADP to create one ATP molecule - CP supplies are exhausted in less than 15 seconds

44. Energy for Muscle Contraction Figure 6.10a

45. Energy for Muscle Contraction • Aerobic Respiration - glucose is broken down to carbon dioxide/CO2 & water/H2O, releasing energy – ATP (36 ATP per 1 glucose molecule) - requires a continuous supply of oxygen

46. Energy for Muscle Contraction Figure 6.10b

47. Energy for Muscle Contraction • Anaerobic Glycolosis & Lactic Acid Fermentation - reaction that breaks down glucose without oxygen - 2 ATP per 1 glucose - byproduct is lactic acid which promotes muscle fatigue & soreness

48. Energy for Muscle Contraction Figure 6.10c

49. 3. Muscle Fatigue and Oxygen Deficit • Muscle fatigue - when a muscle can no longer contract • fatigue is the result of oxygen deficit • oxygen is required to get rid of accumulated lactic acid

50. 4. Types of Muscle Contractions • Isotonic contractions – muscle shortens/movement occurs • Isometric contractions – muscle doesn’t shorten/movement doesn’t occur