N 163: Muscles

57. Identify the ways in which ATP is used to directly power muscle contraction events.

- ATP supplies the energy to move & detach myosin form actin in the cross bridges -Operate the calcium pump in the SR. return Na+ and K+ to the cell exterior/interior after excitation contraction coupling

102. Describe the stress-relaxation response.

. initially when smooth muscle is stretched, smooth muscle responds w/ more vigorous contractions briefly . soon the muscle adapts to its new length & relaxes & still retains the ability to contract on demand . allows hollow organs to accommodate greater volume w/out stronger contractions that would expel its contents

101. Describe the relationship between resting length and tension development in smooth muscle.

. smooth muscle can function and generate much more tension/force at longer lengths more than skeletal muscle, . can contract when its half resting length up to twice the resting length

53. Describe the process of signal transmission at the neuromuscular junction (i.e., communication of nerve AP to the muscle fiber).

1. Action potential arrives at axon terminal of the motor neuron. 2. Voltage-gated Ca ions channels open. Ca enters the axon terminal, moving down the electrochemical gradient. 3. Ca entry causes ACh to be released by exocytosis from the synaptic vesicle. 4. Ach diffuses across the synaptic cleft and binds to its receptors on the sarcolemma. 5. Ach binding opens ion gated channels in the receptors and allow Na+ i to into the muscle and K+ out. This produces a change in the local potential of the membrane called End plate potential. 6. The end potential ignites an action potential by spreading to adjacent membrane areas and opening the voltage-gated sodium channels there. 7. The action potential propagates (moves along the sarcolemma) in all directions,like the way a ripple moves in water. 8. ACh effect is terminated by its breakdown in the synaptic cleft by acetylcholinesterase.

55. What two factors permit relaxation?

1.When Ca2+ is low (tropomyosin covers the active site on actin). 2. ACh is not bound to the receptors in the motor end plate, because then the Na channels are closed and cannot continue the muscle action potential

62. What is a muscle twitch?

A motor unit's response to a single action potential of its motor neuron. The muscle fibers quickly contract and then relax.

51. What is the synaptic cleft?

A space btwn the axon terminal and the muscle fiber.

31. Which protein covers the active sites on the actin filament in a resting muscle fiber?

Actin. Tropomyosin.

69. What role does complete tetanus play in voluntary movements?

Allows the muscle to reach maximum tension and sustain contractions at this level. Infrequent in the real word. Results in superhuman strength, but vigorous activity can't last forever. Leads to extreme muscle fatigue b/c muscle can't contract and the tension drops to zero.

83. What is meant by the term excess post-exercise oxygen consumption (EPOC), which was formerly called "oxygen debt"? What accounts for EPOC?

Also called "recovery oxygen uptake". It's the extra amount for Oz that the body must take in for restorative processes post exercise. EPOC- The diff btwn the amount of O2 needed for total aerobic activity and the amount actually used. All anaerobic sources of ATP used during muscle activity contribute to EPOC. Looking at extra O2 leftover used to restore the body.

61. What is a motor unit?

An axon of a motor neuron and all the muscle fibers it innervates.

32. Describe the location of the sarcoplasmic reticulum (SR) with respect to the myofibrils.

An elaborate smooth ER. It's interconnecting tubules surround each myofibril the way the sleeve of a loosely crocheted sweater surrounds your arm. Communicate with each other at the H zone.

54. What prevents prolonged stimulation of the muscle fiber by acetylcholine (ACh)?

An enzyme in synaptic cleft (Acetylcholinesterase), prevents continued muscle activation in the absence of neural system activation. Breaks Ach down into building blocks (Acetic acid and choline). This removal prevents continued muscle fiber contraction in the absence of additional nervous system simulations.

76. Which of the above sources (#75) of ATP are produced anaerobically? Which are produced aerobically?

Anaerobic- Direct Phosphorylation, Anaerobic pathway. Aerobic- Aerobic pathway.

34. What is the significance of the Ca 2+-release channels and the Ca2+ active transport pumps in the SR?

Ca release channels release calcium to flow into the sarcoplasm of the muscle fiber, calcium binds to troponin, cause change of shape and tropomyosin removed from the active site allowing the actin to be free and the myosin head can now bind to active site on actin. Ca pumps reclaim calcium ions from the cytosol and troponin again changes shape, tropomyosin blocks actin's myosin-binding sites.--->muscle fibers relax. This active transport allow calcium to filter out of the sarcoplasm to allow muscle contraction to cease. Easier to understand: The calcium pumps take back calcium from sarcoplasma which prevents troponin from attaching to the calcium as it likes to do. If troponin isnt binding to calcium, tropomysoin sure as hell aint binding too because its aided in this binding by troponin. Sooo the tropomysoin covers the active site on the actin site once again as is the job of a regulatory protein

97. Identify the regulatory protein in smooth muscle which binds to Ca2+ to activate the contraction process.

Calmodulin.

65. Explain the all-or-none law as it relates to skeletal muscle fibers. explain the all-or-none law as it relates to motor units.

Characteristic of all muscles -A single nerve impulse (via the single motor neuron) elicits a single contraction event in all of the muscle fibers in the motor unit - Does not apply to individual muscles as organs (as a whole) ONE MUSCLE>>ONE CONTRACTION

14. Name and describe the four arrangements of fascicles/fibers within skeletal muscles.

Circular-fascicles are arranged in concentric rings. They surround the external body openings which they close by contracting. Ex) orbicularis around eyes and mouth Convergent-has a broad origin, and its fascicles converge toward a single tendon of insertion. Triangular or fan shaped muscle. Ex:Pectoralis major Parallel- the length of the fascicles runs parallel to the long axis of the muscle of the thigh or spindle shaped w/an expanded belly. Ex: sartorius or Fusiform-biceps or brachii muscle of the arm (spindle) Pennate- fascicles are short and they attach obliquely to a central tendon that runs the length of the muscle. Ex:Deltoid, a)Unipennate=fascicles insert at one side of the tendon b)Bipennate=attaches at both sides c)Multipennate=insert into a large tendon

40. What happens to the A band, I band, H zone, and Z discs during contraction? to sarcomere length?

Contiguous (share a common border w/touching) A band=They will move closer together, but length won't change. I bands=shorten in length H zone= shortens till it disappears Distance btwn successive Z disc will shorten b.c as thin filaments slide centrally toward the center the Z disc are being pulled toward the M line (b/c whole sarcomere shortens).

70. What is recruitment (i.e., multiple motor unit summation)?

Controls the force of contraction more precisely by summoning more muscle fibers into contraction in response to the stimulus. Varied recruitment leads to varied motor unit activation (# of units activated). The more motor units activated= greater external force

71. What is muscle tone, and why is it important?

Definition- Relaxed muscle are almost always contracted. Its due to spinal reflexes that activate first one group of motor units and the on response to activated stretch receptors. Function: Does not produce active movement, but keeps it firm, healthy to respond to stimulation. Skeletal muscle tone also helps to stabilize joints and maintain posture

12. Name and compare the two types of indirect muscle attachments.

Direct (Fleshy,attachments)- the epimysium of the muscle is fused to the periosteum of a bone or perichondrium of a cartilage. Indirect- the muscle's CT wrappings (Epimysium) extend beyond the muscle either as a ropelike tendon or a as a sheetlike aponeurosis. It anchors the muscle to the CT covering a skeletal element (bone or cartilage) or to the fascia of other muscles. Much more common b/c of durability(collagen fibers) and size(conserve space).

78. Which of the above sources (#75) provides energy to fuel brief, high-intensity activity?

Direct Phosphorylation.

75. Name and describe the muscle fiber's three avenues of ATP production.

Direct phosphorylation- When ATP stored in the cell are consumed, creatine phosphate- a high energy molecule stored in muscle- is tapped to generate ATP while adjusting to the high energy demanded. Coupling CP and ADP transfers energy and a phosphate group from CP to ADP to form ATP almost immediately. Anaerobic- Energy source is glucose. The glucose is broken down from glycogen or delivered from blood. No oxygen used. Results in 2 ATP, pyruvic acid and a lactic acid that is released into the blood stream. Aerobic- Glucose is broken down from glycogen breakdown or delivered from blood. Uses O2 and 32 ATP produced per glucose.

39. Muscle contraction is currently best described by the sliding filament theory. Why is this name appropriate for the contraction process?

During contraction,thin filaments slide past thick filaments so that the actin and myosin filaments overlap to a greater degree. Named contraction because the muscle shortens because the I bands shorten and the H zone disappears. Both thin and thick filament do not shorten.

27. Describe the structure of a myosin molecule. How are myosin molecules arranged to make up a thick filament?

Each molecule consist of 2 heavy and 4 light polypeptide chain. Has a rod like tail attached by a flexible hinge to two globular heads. The tail consists 2 of intertwined helical polypeptides polypeptide. The globular heads link the thin and thick filaments causing cross bridges during contraction(sticks out of the thick filament). About 300 myosin , the head face outward at the end of each thick filament. The central portion of the thick filament (H zone) are smooth, but the outside is studded

72. What type of tension does a muscle develop when it is acting as an agonist?

Eccentric contractions

74. What type of tension is being produced when the overall length of the muscle is increasing while the muscle is functioning?

Eccentric. Remember Eccentric>>> Extend

89. Which fiber type has the fastest contraction speed? the slowest?

Fast Glycolytic fibers Slow oxidative fiber.

60. What happens to force production in a muscle that is in extreme stretch or contraction?

Force production can no longer reach maximum strength, so tension occurs little to nothing at all. Or.. Muscle tension develops but the muscle does not shorten.

36. What is the function of the T tubules?

Function: Increase the surface area of the muscle fiber. Because they are continuations of the sarcolemma, they conduct impulses to the deepest regions of the muscle cell and sarcomere to ensure contraction of the muscle at the same time.Makes sure microfibirls contarct at the same time and that impulses enter deep regions of muscle cell that cause release of calcium from cisternae

30. Describe the structure of an actin molecule. How are individual actin monomers arranged to make up a thin filament?

G actin bind to make F actin (Filamentous) Its has a kidney shaped polypeptide subunit called the globular actin or G actin. This site bears the active site to which myosin heads attach during contraction. Joined to long actin filaments called filamentous or F-actin. They intertwine, looking like twisted pearls which becomes the backbone of the actin filament. Tropomyosin is the rod shaped & spirals about the actin core. Troponin is globular shaped structure that serves as the binding site for Ca.

58. What is the relationship between the initial length of the sarcomere (or muscle fiber) and the amount of tension it can produce?

Greatest tension when there is optimal overlap btwn thick and thin filament. Occurs just prior to resting length (b4 contraction) near optimal overlap. The bulkier the muscle the greater its cross sectional area=greater tension can occur and strength. The largest fiber of large motor units produce most powerful movements.

41. Which myofibril structures or regions change length during the contraction process?

I bands=shorten in length H zone= shortens till it disappears Distance btwn successive Z disc will shorten b.c as thin filaments slide centrally toward the center the Z disc are being pulled toward the end line (b/c whole sarcomere shortens).

79. Where is most of the cell's ATP produced?

In the glycolysis cycle in the cytoplasm (mitochondria)

81. What is muscle fatigue?

Inability of the muscle to contract even if it is still receiving stimuli

93. What changes are induced in skeletal muscle in response to a program of resistance exercise training? Which muscle fiber types seem to be especially responsive to endurance training?

Increase size of individual fibers. More mitochondria, myofilaments, myofibrillar, glycogen and more CT btwn cells. The fast glycolytic fibers are most resistant to this type of training.

82. What factors contribute to the onset of muscle fatigue?

Ionic imbalances.- As action potential is being transmitted, potassium is lost from the muscle cell, and results in the accumulation of fluid in the T tubule. This ionic changed disturbs the membrane potential of the muscle cell and halts Ca release from SR. Accumulation of inorganic phosphate from CP and ATP also interferes with the release of ATP. Lactin. In general- For short exercises, its ionic imbalances that alter E-C coupling. For long ones,

73. What type of tension is being produced when internal tension is being developed, but no movement occurs?

Isometric contraction

25. What is the function of the Z disc?

It anchors myofilaments to sarcolemma. Aids elastic filament extends from it to the thick filament to the M line

64. What is taking place during the relaxation period?

Lasts 10-100ms, is initiated by reentry of Ca2+ into the SR. Calcium concentrations in the sarcoplasma is going back to the baseline. Bc the number of active cross bridges is declining,contractile force is declining. Muscle tension decrease to zero and the racing returns to the baseline. If the muscle shortened during contraction, it now returns to initial length. Notice that a muscle contracts faster than it relaxes, as revealed by the asymmetric nature of the myogram tracing.

90. What is the effect of load and recruitment on the duration of a muscle contraction?

Load- A greater load leads to an increase in latent period, slower shortening and a briefer duration of shortening. Recruitment- The same way more hands do the job faster, the more quickly the job gets done, the more motor units that are contracting, the faster and more prolonged the contractions are.

16. What benefit is provided by a lever that operates at a mechanical advantage? at a mechanical disadvantage?

Mechanical Advan.-Small effort exerted over a relatively large distance can move a large load over a small distance. If the load is close to the fulcrum and the effort is applied far from the fulcrum. Called the Power lever Advantage:requires small effort Mechanical Disadvan.-the muscle force is greater than the load lifted. This occurs when the load is far from the fulcrum and the effort is applied near the fulcrum. Speed lever. Advantage: wide range of motion

103. Smooth muscle can be categorized as single-unit smooth muscle (which Marieb calls "unitary smooth muscle) or multi-unit smooth muscle. Describe the ways in which these two types of smooth muscle differ.

Most basic lvl, the multi-unit is completely dependent on external nerve fibers. A single unit smooth muscle has pacemakers and can be self excited.

14. In indirect attachments, what tissues are involved in transmitting pulling (i.e., tension forces generated during contraction) forces from the muscle fiber to the bone?

Muscles CT- Made up of collagen fibers which can withstand abrasion and tears.

6. Describe the gross anatomy of a muscle, beginning with the myofibrils.

Myofibrils run the entire length parallel to muscle fibers )each muscle fiber has 100s-1,000s of myofibrils) that are responsible for contraction. Within the myofibrils are sarcomeres (rod-like structures). At the end, they anchor into the sarcolemma, which has proteins that anchor it to the endomysium.

52. What is acetylcholine? What role does it play at the neuromuscular junction?

Neurotransmitter, when it is release it causes a change in sarcolemma permeability leading to a change in membrane potential.

84. What 4 factors influence the amount of force that a muscle generates during contraction?

Number of muscles recruited- The more units recruited, the greater the force. Size of the muscle fiber- The bulkier the the muscle, the greater the cross sectional area, the more muscle it can develop. Frequency of stimulations- When a muscle is stimulated more frequently, contractions are summed up, becoming more vigorous and ultimately producing tetanus. Degree of muscle stretch- If a muscle is stretched to various length and stimulated, the tension of the muscle generated varies with length. Optimal length.

80. What happens to pyruvic acid when there is not enough O2 present to completely hydrolyze it?

Ordinarily, it would enter the mitochondria and react with oxygen to produce more ATP. But for muscles during a heavy physical activity, muscles do not get enough oxygen supply so the Pyruvic acid is converted into lactic acid and diffuses into the liver, heart or kidneys where they are used as energy source.

50. What specializations of the muscle fiber (at the motor end plate) enable it to respond to signals from the motor neuron?

Presence of synaptic cleft

33. What is the function of the SR and terminal cisternae?

SR- run longitudinally along the myofibril, communicating with each other at the H zone. -----has calcium pumps + calcium channels Function- Stores and regulates calcium ions when in demand for the muscle to contract. Terminal Cisterns- form larger, perpendicular cross channels at the A band-I band junctions, and they always occur in pairs.Both involved in producing the energy used during contraction.

106. Which type of smooth muscle exhibits rhythmicity and self-excitation?

Single unit

77. Which of the above sources (#75) provides energy to fuel prolonged, submaximal activity?

Slight burst of activities- ATP and CP Slightly longer activities- Anaerobic Prolonged activies like a marathon- Aerobic respiration using both glucose and fatty acids as fuels.

87. Classify each muscle fiber type with respect to its predominant pathway for ATP synthesis, the amount of myoglobin present, and the activity of its myosin ATPase

Slow oxidative fiber (slow twitch) - high,slow Fast oxidative glycolytic fibers (Fast twitch)-intermeidate,fast Fast glycolytic fibers (fast twitch)-low,fast

92. What changes are induced in skeletal muscle in response to a program of endurance (i.e.,"cardio") exercise training? Which muscle fiber type is most responsive to endurance training?

Slow oxidative fibers are the most responsive, and the number of capillaries that surround the muscle fibers increase.Mitochondria increase. Fiber synthesize more myoglobin. pg.307

88. Which fiber type receives the richest blood supply?

Slow oxidative fibers. Table 9.2 and the notes above it

94. Describe the major structural and functional differences between smooth and skeletal muscle.

Smooth- smooth,no striations and involuntary. Found in walls of hollow visceral organs. Skeletal- striated and involuntary. Responsible for locomotion and manipulation

56. Describe the entire process of excitation-contraction coupling, beginning with a nerve impulse in a motor neuron.

Step 1: Action potential sweeps along sarcolemmal and down the T tubules Step 2: When it reaches( action potential) reaches the triad it causes the voltage sensitive tubule proteins to change shape. This shape change causes the Ca2+ to flood out of the terminal cisternae of the SR into the sarcoplasm. a)Ca leaves SR so quickly b/c in very high concentration in SR compared to the sarcoplasm (b/c huge gradient) b) Calsequestrin=protein in the SR enhances Ca effects by increased Ca storage capabilities. Step 3: Ca binds to troponin. Causes troponin to change shape and to pull tropomyosin away from active site on actin. Step 4: Cross bridge cycling continues as long as the sarcoplasmic Ca is elevated. Step 5: Intracellular Ca level falls as ATP dependent Ca pumps in SR sequestering (take back) the Ca. Step 6: Ca lelvels low in SR = tropomyosin moves back over the active sites on actin---> crossbridge cycling stops.

47. When is the (ADP + Pi ) which fueled the power stroke released from the myosin head?

The ADP falls off right before the power stroke and the P falls off after the ATP is hydrolyzed.

49. Describe the structure of the neuromuscular junction.

The axon of each motor neuron (the nerve cell that activates skeletal muscle fibers) divides profusely as it enters the muscle. Each axon gives off several shorts curling branches that collectively form the neuromuscular junction or motor end plate with a single muscle fiber. Or In short----It the the specialized contact between a motor nerve ending and a muscle cell. The point where the nerve synapses meets the muscle fiber. It includes the axon terminals, synaptic cleft, and the junctional folds (The trough-like sarcolemma that is highly folded and found at the junction.) Txtbk 9.4 under the nerve Stimulus and events at the neuromuscular junction.

63. What is the latent period and what is taking place during the latent period?

The first few milliseconds following stimulation when excitation-contraction coupling is occurring. During this period, cross bridges begin to cycle but muscle tension isn't yet measurable and the myogram doesn't show a response. Chemical changes occur intracellularly in preparation for contraction, such as release of calcium from the sarcoplasmic reticulum

86. How does the size of a motor unit influence the strength of contraction and the control of a movement?

The greater bulkier the muscle and the greater the cross-sectional area,the more tension it can develop.

91. What is the effect of load on the velocity of contraction?

The lighter the load, the more the velocity of contraction.

48. What causes myosin to detach from actin after the power stroke is completed?

The re-attachment of an ATP to the myosin causes it to detach from the actin.

24. What is a sarcomere?

The region of a myofibril between two successive Z discs. Its the smallest contractile unit of a muscle. FUNCTIONAL UNIT OF MUSCLE FIBER

67. What happens to the strength of contraction when two or more identical stimuli are delivered to the muscle in rapid succession (i.e., before complete relaxation occurs)? What is this phenomenon called?

The second twitch/stimuli/wave (myograms show action potential) is stronger than the first. It happens straight after the first w/o relaxation. It's caused wave summation or temporal summation. Second contraction-causes more shortening than the 1st. Refractory period is honored, if 2nd stimulus comes after re-polarization but b4 muscle relaxation is complete then wave summation will occur. Wave summation contributes to contraction force, but primary function is to produce smooth muscle contractions by rapidly stimulating muscle cells.

10. What is the location of the blood vessels and nerves which supply the skeletal muscle tissue?

These structures all enter or exit near the central part of the muscle and branch profusely through its CT sheath. (Txtbk 9.2- A skeletal muscle is made up of muscle fibers,nerves,blood vessels and CT tissues)

59. Describe the relative positions of actin and myosin when the muscle is at its optimal length for strength production.

They are partially overlapped. The ideal length tension relationship occurs when muscle is slightly stretching. Thin/thick ligaments are partially overlapped and so there is a potential that allows sliding over entire length of thin filament.

13. Relative to muscle function, what is the significance of Sharpey's fibers?

They attach the muscle to the periosteum of the bone. They intertwine with the fibers of ligaments and tendons to help anchor those structures to the one & also to distribute mechanical forces over a greater surface of the bone. They make the bone resist any pulling.

26. Identify the two primary types of myofilamentsfound in myofibrils.

Thick filaments- Extend the entire length of the A bands. Interconnected in the middle of the sarcomere at the M band. Made up of myosin Thin filaments- Has actin. Extend across the I band ad partway to the A band.

44. What is the role of ATP and the myosin head in the sliding filament mechanism?

Thin filaments continue to slide as long as Ca signals and adequate ATP are present. As muscles contract ATP supplies energy to move and detach crossbridges,operates pump in the SR, returns Na and Ka to exterior of cell(3 Na) and interior(2 K) of cell. after excitation contraction coupling. Only source of energy used directly for contractile activities,must be regenerated as fast as it is broken down.

17. What is the most common class of lever system in the in the body? Where is the fulcrum with respect to the load and effort in this lever system?

Third class lever, effort is btwn the load and the fulcrum. Permits the muscle to be inserted really close to joint, and allows for rapid extensive movement. Relatively little shortening of the muscle. Ex: Biceps (flexing the forearm: fixed joint is fulcrum and the load is what is in the hand and the effort is exerted in the forearm(proximal radius).

37. Why is the triad of functional significance?

Triad= T tubule + terminal cisternae adjacent to it. Integral proteins that extend from T tubules into the inter membrane space act as voltage sensors. The protruding integral proteins of the SR form gated channels through which terminal cisternae produce Ca. The integral protein of the terminal cisternae also extend into the intermembrane space, they regulate the realssd of Ca into the SR

43. Specifically, how do troponin and tropomyosin help regulate the contraction process?

Tropomyosin blocks the active sites of actin to prevent binding to active sites by myosin heads. Troponin- Controls the action by causing conformational change that removes tropomyosin from covering the active site on actin

29. Which of the proteins identified above (#28) is/are regulatory proteins?

Troponin(globular 3 polypeptide complex) and tropomyosin (spirals around actin core, stiffens and stabilizes actin core)

96. What are the sources of the sarcoplasmic Ca 2+ which triggers smooth muscle contraction? Which of these is the main source?

Tubules of SR release Ca2+ and Ca2+ moves into the cell from the extracellular space via membrane channels. I think the main source Of Ca2+ enters through channels from the extracellular space. The second one is the main source.

35. What are the T tubules? Where are they located?

Tunnel-like Inward invaginations in sarcolemma that run deep into the cell between terminal cisternae. Extend into sarcoplasma at right angles cell surface

38. What causes Ca2+ to be released from the terminal cisternae?

When action potential reaches the triad.

42. What is the role of Ca2+ and the regulatory proteins in the sliding filament mechanism?

When intracellular calcium levels are low, the muscle is relaxed, and tropomyosin molecules physically block the active site on actin. Levels of calcium increase, providing the final trigger for contraction

45. At what point in cross bridge cycling does ATP become hydrolyzed, and provide the energy for activation of the myosin head?

When the ATP attaches to the myosin head at the active site, it becomes hydrolyzed

46. At what point (#45) does the power stroke occur?

When the myosin is in its high-energy configuration and it begins to rotate toward the center of the sarcomere, the power stroke occurs. This is at the point of attachment when the ADP falls off.

28. Identify the proteins which make up thin filaments.

a.)Actin- Bears the active site to which myosin heads attaches to. b.)Tropomyosin- Rod -shaped protein, spiral about the actin core and helps stiffen and stabilize the actin. Arranged along the actin molecule. Function: In a relaxed muscle, they block the myosin-binding site on actin so that myosin heads in the thick filaments cannot bind to the thin filament.c.) Troponin- A polypeptide complex that has 3 subunits.One is an Inhibitory subunit that binds to actin. Another subunit binds to tropomyosin to help position it on actin. Another binds to calcium ions.

98. What is the role of myosin light chain kinase (MLCK)?

activated calmodulin interacts with myosin light chain kinase enzyme which goes to phosphorylate myosin, activating the myosin ATPases

105. What is the role of gap junctions and pacemaker cells in single-unit smooth muscle?

gap junctions- allow smooth muscles to transmit action potentials from fiber to fiber, how smooth muscles contract in synchronization pacemaker cells- are self excitatory, set the rhythmic pattern of contraction

95. What structures anchor smooth muscle fibers and transmit the tension they develop?

intermediate filaments, dense bodies

100. How is smooth muscle contraction regulated?

neural regulation (nerves) can be via action potentials/ neurotransmitters - those smooth muscles w/ nerve supply can still respond to local factors . local factors (chemical changes)- those smooth muscle layers w/ no nerve supply local factors that influence contraction include: hormones, pH, other chemical factors

21. Describe how the following organelles are modified or adapted for function in skeletal muscle tissue: nucleus; mitochondria; smooth endoplasmic reticulum

nucleus- muscle fiber is multinucleated smooth endoplasmic reticulum- smooth elaborate, interconnecting tubules surround each myofibril, mostly run longitudinally (like a crochet sleeve), usually located closely to mitochondria & glycosomes at A band/ I band junctions are perpendicular tunnels that always come in pairs called terminal cisternae, these are also part of the SRnMitochondria- More mitochondria for the muscle needs energy to contract. Smooth Endoplasmic Reticulum- It covers a muscle and has a new name called Sarcoplasmic Reticulum.

104. Where is each type of smooth muscle located?

single unit- most common, fibers organized into sheets of cells which contract as a single unit, connected via gap junctions, have pace maker cells usually that set rhythmic pace( other words self excite), but can also be excited externally multi unit smooth muscle- fibers that are structurally independent of each other, no gap junctions, innervated by nerve fibers from the autonomic nervous system, completely dependent on external source of innervation, not self excitatory single unit- found in hollow organs except the heart multi unit smooth muscle- found in lungs, large arteries, pupils, arrector pilli muscles of hair follicles

99. Which contracts more quickly -smooth or skeletal muscle? Which contracts more efficiently? Which is most fatigue-resistant?

smooth muscle takes about 30 x's longer to contract & relax than skeletal muscle, & uses ATP more efficiently, can maintain contraction while not using ATP, more fatigue resistant than skeletal muscle

15. What is the advantage of the parallel arrangement of fibers? of the pennate arrangement? the convergent?

the longer and the more nearly parallel the muscle fibers are to a muscle's long axis the more the muscle can shorten. The bipennate and multipennate muscle would be the most powerful b/c they pack in the most fibers,but shorten very little. The convergent advantages: shorter fibers, good for pulling, provider for more power

68. What is the difference between unfused tetanus and complete tetanus? How is complete tetanus achieved in a muscle fiber?

unfused tetanus or incomplete tetanus- normal, frequent stimulation occurs so muscle does not completely relax. Degree of wave summation gets higher & higher. Tension reaches a peak, but vacillating level. Complete tetanus- As the stimulations increase, the muscle tension reaches maximum. At this point, all the evidence of muscle relaxation disappears and the contractions fuse into a smooth, sustained contraction plateau. achieved: constant stimulus would have to occur, but it does not happen in the body

66. What are graded muscle responses? What are the two general ways of producing a graded muscle response?

variations in the degree of muscle connotation by changing either the frequency or strength of the stimulus a)Muscle Response to Changes in Stimulus Frequency-The Nervous system achieves greater muscular force by increasing the firing rate of motor neurons. For example, if two identical stimuli (electrical shocks or nerve impulses) are delivered to a muscle in rapid succession, the 2nd twitch will be stronger than the first. On a myogram the 2nd twitch will appear to ride on the shoulders of the first. Its called a wave. Occurs because the second contraction occurs before the first one has completely relaxed. b)Changing the Strength of stimulation- Multiple Motor Unit Summation or recruitment controls the force of contraction. Achieved in the lab by delivering shocks of increasing voltage to the muscle, calling more and more muscle fibers into play.

85. When does a muscle begin to develop (or exert) external tension?

• After internal tension is developed, continued cross-bridge cycling generates external tension o When internal tension exceeds the resistance • External tension is the tension exerted against the bone at the muscle attachment site o If it is great enough, it will cause movement