Muscle Tissue

1. Muscle Tissue Chapter 11 Part 2

2. Excitation (steps 1 and 2) Nerve signal opens voltage-gated calcium channels. Calcium stimulates release of synaptic vesicles containing ACh = ACh release into synaptic cleft.

3. Excitation (steps 3 and 4)

4. Excitation (step 5)

5. Excitation-Contraction Coupling (steps 6 and 7) Action potential spreading over sarcolemma enters ________________ -- channels open in T tubules causing ____________ to open in SR

6. Excitation-Contraction Coupling (steps 8 and 9) Calcium released by SR binds to _____________ Troponin-tropomyosin complex changes shape and __________________________________

7. Contraction (steps 10 and 11) Myosin ATPase in myosin head hydrolyzes an ATP molecule, activating the head and �cocking� it in an extended position It binds to actin active site forming a _____________

8. Contraction (steps 12 and 13) __________________ = myosin head releasesADP and phosphate; it bends pulling the thin filament past the thick With more ATP, the myosin head attaches to a new active site Bound heads prevent slippage thin and thick filaments do not become shorter, just slide past each other (__________________________)

9. Relaxation (steps 14 and 15) Nerve stimulation ceases and ____________________ removes ACh from receptors. Stimulation of the muscle cell ceases.

10. Relaxation (step 16) __________________________________ __________________________________ ATP is needed for muscle relaxation as well as muscle contraction

11. Relaxation (steps 17 and 18) Calcium loss from sarcoplasm moves troponin-tropomyosin complex over active sites Muscle fiber returns to its resting length

12. ________________________ _________________________________________ Deteriorating sarcoplasmic reticulum releases calcium Calcium activates myosin-actin cross-bridging and muscle contracts, but can not relax. ___________________________________ ATP production stops at death Fibers remain contracted until myofilaments decay

13. Length-Tension Relationship _______________________ _______________________ _______________________ Overly contracted (weak contraction results) thick filaments too close to Z discs and can�t slide Too stretched (weak contraction results) little overlap of thin and thick not many cross bridges form Optimum resting length produces greatest force when muscle contracts cns maintains optimal length producing muscle tone or partial contraction

14. Muscle Twitch in Frog ____________________ ____________________ ________________________________________ a single brief stimulus produces a quick cycle of contraction and relaxation called a twitch (lasting less than 1/10 second) A single twitch contraction is not strong enough to do any useful work

15. Muscle Twitch Phases twitch contraction ________________________ (2 msec delay) no visible contraction occurs elastic components are being stretched contraction phase ___________________________________ ________________________________ loss of tension and return to resting length as calcium returns to SR

16. Contraction Strength of Twitches Threshold stimuli produces twitches _________________________________

17. Recruitment and Stimulus Intensity Stimulating the muscle with higher voltage produces stronger contractions More motor units are recruited multiple motor unit summation lift a glass of milk versus a whole gallon of milk

18. Twitch and Treppe Contractions Muscle stimulation low frequency (up to 10 stimuli/sec) each stimulus produces an identical twitch response moderate frequency (between 10-20 stimuli/sec) each twitch has time to recover but develops more tension than the one before (treppe phenomenon) __________________________________________ heat of tissue increases myosin ATPase efficiency

19. Incomplete and Complete Tetanus Higher frequency stimulation (20-40 stimuli/second) generates gradually more strength of contraction each stimuli arrives before last one recovers temporal summation or wave summation incomplete tetanus = sustained fluttering contractions Maximum frequency stimulation (40-50 stimuli/second) muscle has no time to relax at all twitches fuse into smooth, prolonged contraction called complete tetanus rarely occurs in the body

20. Isometric and Isotonic Contractions _________________________________________ develops tension without changing length important in postural muscle function and antagonistic muscle joint stabilization _________________________________________ tension while shortening or lengthening

21. ATP Sources Muscle contraction depends on ATP ATP synthesis ______________________ (ATP production limited) ______________________, produces toxic lactic acid _________________________ (more ATP produced) requires continuous oxygen supply, produces H2O and CO2

22. Immediate Energy Needs Short, intense exercise (100 m dash) oxygen supplied by ________________ _______________ system myokinase transfers Pi groups to ATP creatine kinase transfers Pi groups from creatine phosphate to make ATP Result is power for a 1 minute brisk walk or 6 seconds of sprinting

23. Short-Term Energy Needs ________________________ system takes over produces ATP for 30-40 seconds of maximum activity playing basketball or running around baseball diamonds muscles obtain glucose from blood and stored glycogen

24. Long-Term Energy Needs Aerobic respiration (prolonged exercise) Produces _____________ATPs/glucose molecule

25. Fatigue Progressive weakness from use ATP synthesis declines as glycogen is consumed sodium-potassium pumps fail to maintain membrane potential and excitability lactic acid inhibits enzyme function extracellular K+ accumulates hyperpolarizes the cell motor nerve fibers use up their acetylcholine

26. ______________________ Heavy breathing after strenuous exercise excess post-exercise oxygen consumption (EPOC) Purposes for extra oxygen __________________________ (myoglobin, blood hemoglobin) replenishes the phosphagen system ____________________________________

27. Slow- and Fast-Twitch Fibers __________________________________ more mitochondria, myoglobin and capillaries adapted for aerobic respiration and ____________ to fatigue soleus and postural muscles of the back (100msec/twitch)

28. Slow and Fast-Twitch Fibers Fast glycolytic, fast-twitch fibers rich in enzymes for phosphagen and glycogen-lactic acid systems ______________________________________________________________________ (7.5 msec/twitch) extraocular eye muscles, gastrocnemius and biceps brachii Proportions genetically determined

29. Strength and Conditioning _______________________________ muscle size and fascicle arrangement size of motor units and motor unit recruitment length of muscle at start of contraction Resistance training (weight lifting) stimulates cell enlargement (more myofilaments) Endurance training (aerobic exercise) ______________________________________ ______________________________________

30. Cardiac Muscle __________________________________ Linked by intercalated discs electrical gap junctions allow cells stimulate neighboring cells mechanical junctions hold cells together ________________________________________________________________________

31. Cardiac Muscle _______________ due to pacemaker cells Uses aerobic respiration almost exclusively ________________________________________________________________________ vulnerable to interruptions in oxygen supply

32. Smooth Muscle __________________________ no striations, sarcomeres or Z discs SR is scanty and has no T tubules calcium for contraction comes from extracellular fluid If present, nerve supply is autonomic releases either ACh or norepinephrine

33. Types of Smooth Muscle ________________________________ largest arteries, iris, pulmonary air passages, arrector pili muscles terminal nerve branches synapse on myocytes independent contraction

34. Types of Smooth Muscle ______________________________ most blood vessels and viscera as circular and longitudinal muscle layers large number of cells contract as a unit

35. Stimulation of Smooth Muscle Involuntary and contracts without nerve stimulation _______________________________________ pacemaker cells in GI tract are autorhythmic

36. Features of Contraction and Relaxation Calcium trigger is extracellular Ca+ channels open ? voltage, hormones, neurotransmitters or cell stretching _____________________ _____________________ shortens the entire cell in a twisting fashion

37. Contraction and relaxation very slow in comparison slow myosin ATPase enzyme and slow pumps that remove Ca+2 Uses 10-300 times less ATP to maintain the same tension latch-bridge mechanism maintains tetanus (muscle tone) keeps arteries in state of partial contraction (vasomotor tone) Features of Contraction and Relaxation