The Muscular System

1. The Muscular System

2. Overview: Guiding Questions • What types of cells are found in muscle tissue? • How are these cells specialized to carry out their function? • What does BMI measure?

3. What types of cells are found in the muscle tissue? How are they specialized to carry out their function? Functions Contractile Cells • Pumping blood throughout the body • Moving the skeletal system • Passing food through the digestive system • Specialized cell membrane and cytoskeleton that permit them to change their shape • Cytoskeleton allows shortening in one or more planes (contraction) • Laid out as sheets of muscle tissue that produce coordinated contractions

4. What do contractile cells need to carry out their function? High energy needs Glucose Remove metabolic wastes Blood Supply Electrolytes calcium Oxygen From bones

5. What does BMI measure? • Compares the amount of muscle mass with the body fat composition. • A certain degree of leanness is known to reduce heart disease and metabolic disorders.

6. Muscle: What are contractile proteins? How can we classify muscle tissue? Voluntary or Involuntary Contractile proteins: Proteins of the cytoskeleton involved in contraction (shortening) of muscle cells Appearance Location

7. Appearance Striated Non-Striated Uniform arrangement of contractile proteins Can see microscopically Stronger Contractions Randomized pattern of contractile proteins Cannot see microscopically Weaker contractions

8. Voluntary or Involuntary • Large degree of control • Some unconsciously (breathing) • Some contractions are intentional • Contract without conscious control • Jobs that are automatic or in conjunction with other organ systems Voluntary Involuntary

9. Location Cardiac Skeletal Smooth Make up the heart Striated Connected by intercalated disks Involuntary Large cells with distinct striations Strong directional contractions Attach to bones and joints that produces body movement Most are voluntary Spindle or teardrop cells Fibers not visible Weak contractions that last a long time Linings of BVs Tubular organs Most involuntary

10. Types of Muscle Tissue: Guiding Questions • Briefly describe myogenesis. • Briefly characterize the three types of muscle cells • How do contractile proteins contribute to skeletal function? • Why is the “intrinsic beat” of cardiac muscle cells significant? • Why is “peristalsis” significant? • Describe the relationship between muscle cells and muscle fibers

11. Briefly describe myogenesis: • Muscle develops in mesoderm cells: myogenesis • Stem cells form myoblasts • Myoblasts move to other developing tissues to form the 3 muscle types • Growth factors (chemicals that act as signals to initiate cell division & differentiation) by tissues give direction as to what type of muscle needs to form.

12. Briefly Characterize the 3 Types of Muscle Cells Cardiac Skeletal Smooth • Form around large BV and form heart • Strong contractions • Not conscious control • Have 2 nuclei per cell • Cells are branched • Communicate thru intercalated disks • Intrinsic beat: all cardiac cells act in unison, coordinated thru intercalated disks • Provides movement • Large cells with distinct striations • Powerful contractile capabilities • One cell is composed of several myoblasts that fuse into a muscle fiber—why so many nuclei? • Each fiber stimulated by a motor nerve cell that controls several muscle fibers at once • Lining of BV, digestive organs, urinary system, respiratory system • Nonstriated • Weak involuntary contractions can last for a long time • Dilation and constriction of BV and tubular structures in respiratory system • Peristalsis: laid in sheets in digestive system. Moves food & wastes through

13. Cardiac Muscle: Branching, striated cells fused at plasma membranes. Skeletal Muscle: Long, striated cells with multiple nuclei Smooth Muscle: Long, spindle-shaped cells each with a single nucleus

14. What type of muscle cells?

15. Now, you should be able to answer these questions! • How do contractile proteins contribute to skeletal function? • Why is the “intrinsic beat” of cardiac muscle cells significant? • Why is “peristalsis” significant? • Describe the relationship between muscle cells and muscle fibers

16. Muscle Cell Structure Guiding Questions • Describe the basic structure of skeletal muscle cells • Briefly summarize the various types of fibers found in a muscle cell • Describe the relationship between myofibrils, muscle fibers, and fasciculi • Why is a sarcomere called the “contractile unit” of the muscle?

17. Organization of (skeletal) muscle • Skeletal muscle fibers located in muscles • Entire muscle surrounded by epimysium, a CT layer • Subdivided into fiber bundles called fascicles (fasciculi) • Fascilcles surrounded by perimysium, also CT

18. Membranes • Portions of perimysium extend into the endomysium • Thin layer of CT that covers each muscle fiber • Muscle fiber (bundle)= multinucleate cell

20. SARCOMERE • Sarcomere= basic (functional) contractile unit • Separated by each other by dark Z lines/discs • Actin & myosin slide past each other as the muscle contracts • Contraction requires Ca2+ and ATP Actin Myosin Sarcomere

21. Other Key Points About Sarcomeres • Z-line/disc – vertical protein bands that hold sarcomere to sarcolemma. • I Bands • Lighter areas of non-overlap between actin and myosin • Contain the Z-lines. • Dark Bands = A Bands • Areas where some overlap occurs • = “Striations” on the slide • Coincide with the length of myosin myofilaments. • H-zone – light area within A-band

22. Sarcoplasmic Reticulum • Each myofibril is surrounded by network of tubes and storage sacs (Transverse tubules and sarcoplasmic reticulum) • Releases Ca2+ ions when stimulated by motor neuron • Triggers contraction (more on this later…)

23. MICROSCOPIC STRUCTURE • Muscle FIBERS: grouped into bundles (fasciculi) • = 1 cell! • Fibers contain myofibrilswith: • ACTIN: thin myofilaments • Also contain: • Tropomyosin • Troponin • MYOSIN: thick myofilaments, with “swiveling” arm and head • TITIN: elastic fibers that hold myosin in place, controlling stretch of sarcomere

26. Another look…

27. Muscle Cell Function Guiding Questions • How would a muscle appear to change microscopically during a contraction? • What are the three stages of muscle contraction? • What is the role of neurotransmitters during muscle contraction? • Describe the ion concentrations found inside and outside a resting muscle cell • Briefly describe the events that occur during the muscle contraction phase. • What is the role of ATP during this phase? • What must occur for a muscle cell to “fully” recover after a contraction? • What occurs during “rigor mortis”?

28. Muscle Contraction • Sarcomeres shorten, distance between z-lines reduced • Thick and thin myofilaments overlap more during contraction • 3 stages: • Neural stimulation • Muscle cell contraction • Muscle cell relaxation

29. Motor Unit • Stimulation of a muscle by a nerve impulse (motor nerve) is required before a muscle can shorten • Neuromuscular junction: point of contact b/w nerve ending and the muscle fiber it innervates. • Motor unit: motor neuron + muscle cell

30. Neuromuscular Junction

32. Neural Stimulation • Motor neuron releases neurotransmitters to stimulate a contraction • Acetylcholine (Ach) binds to receptors located on sarcolemma • Changes transport proteins found in sarcolemma • Alters transport of ions • Normally, more Sodium (Na+) ions outside muscle cell, while Potassium (K+) higher inside • Sodium/Potassium pumps maintain this unequal concentration •  Excitable condition

33. When stimulated, ion channels open, depolarizing the cell • Na+ flows in, K+ out •  sarcoplasmic reticulum releases stored calcium • Ca2+ travels to sarcomere, initiating muscle contraction phase

34. Muscle Contraction Animation • Click here to view animation

35. Sliding filament theory Ca2+ • In the absence of Calcium ions… • Troponin“hat” sits on Tropomyosin filament • These blocks access to the myosin head’s binding site on actin. Troponin Tropomyosin

36. When Calcium is released by the Sarcoplasmic reticulum • it diffuses into the muscles • binds to the troponin “hat” • shifting both the troponin and tropomyosin filament

37. Myosin splits ATP and undergoes a conformational change into a high-energy state. • The head of myosin binds to actin • Forms a cross-bridge between the thick and thin filaments.

38. The energy stored by myosin is released • ADP and phosphate released from myosin. • The myosin molecule relaxes • Causes rotation of the globular head • This leads to the sliding of the filaments. • This cycle continues until Ca2+ ions gone (and stimulus stops)

39. ATP binds to cross bridge, causing cross bridge to disconnect from actin. • Splitting of ATP leads to re-energizing/ repositioning of the cross bridge.

40. Relaxation Phase • Complete contraction of muscle cell requires several cycles of neural stimulation and contraction phases • Ca2+ ions transported back to sarcoplasmic reticulum (req. ATP) • When the calcium level decreases • troponinlocks tropomyosinback into the blocking position • thin filament (actin) slides back to the resting state (when ATP binds to myosin head)

41. Relaxation phase occurs when no more neural stimulations are exciting the sarcolemma • Na+/K+ pump returns ions to resting state • Muscle cell remains in contracted, but pliable state • Must be “stretched” back into position

42. Review of the Role of ATP • ATP transfers its energy to the myosin cross bridge, which in turn energizes the power stroke. • ATP disconnects the myosin cross bridge from the binding site on actin. • ATP fuels the pump that actively transports calcium ions back into the sarcoplasmic reticulum.

43. Rigor Mortis • In death… • Calcium leaks out of sarcoplasmic reticulum into sarcomere • Causes muscle tension = rigor mortis • Muscle cell structures start breaking down, causing muscle to loosen (unless body becomes dehydrated)

44. Creatine phosphate • Stores energy in muscle cells • Collects energy from ATP, stores for long periods of time • Transfers back to ATP when needed

45. Glycogen • Stored form of glucose • Energy reserve for muscle action • Continuous supply needed to produce ATP

46. Myoglobin • Red pigment that stores oxygen for muscle cells • “Grabs” oxygen from hemoglobin in blood • High affinity for oxygen • Allows cells to produce large amounts of ATP

47. Musculature Guiding Questions • What determines a muscle’s morphology? • Distinguish between a muscle’s origin and insertion

48. Gross Skeletal Muscle Types Guiding Questions • Review the location of the various gross skeletal muscle types listed on page. 231 • List, and briefly describe, the various terms that describe the muscle structures, patterns, and shapes

49. Parallel or Pinnate • Parallel • general-purpose muscles • Sheets of muscle cells that run in the same direction • Contractions for moving light loads over a long distance • Pinnate • Feather-pattern • Great strength for moving heavy loads over a short distance • Strong movements for the arms and legs

50. Gross Muscle Cell Types/Terms