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Block 3 Up To Quiz 1 > Skeletal Muscle Pt2 > Flashcards

Skeletal Muscle Pt2 Flashcards

1
Q

Contraction of motor unit initiated from

A

CNS, occurs as all or noting twitch response

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2
Q

Contraction of motor unit steps

A
  1. Alpha-motor neuron propagates actio potential to muscle
  2. Acetylcholine released, binds at muscle endplate
  3. Channels in nicotinic receptors open -> Na+ diffusion into cell
  4. depolarization at motor endplate
  5. If enough miniature endplate potentials -> full fledged end plate potential
  6. Voltage gated Na+ channels open -> self propagating action potential spreads involving entire plasma membrane including T-tubule system membrane invaginations
  7. Voltage gated Ca2+ channels in T-tubules open
  8. Voltage-induced confrontational change t-tubule channel -> Ca2+ release channels opening
  9. Ca2+ flows out SR through release channels
  10. Large rapid increase in cytoplasmic calcium concentration
  11. Ca2+ binds troponin C
  12. Conformational change in troponin complex -> change troponin complex
  13. Conformatinal change troponin complex pulls tropomyosin out of normal position on actin
  14. myosin heads bind acting forming cross-bridges
  15. myosin head hydrolyzes ADP uses energy ATP hydrolysis to walk along actin filament
  16. Ca2+ removed from cytoplasm by Ca2+-ATPase of SR membrane
  17. Cytosolic Ca2+ concentration decreases
  18. Ca2+ released from troponin C
  19. Tropomyosin returns to resting portion blocking myosin binding sites on actin filaments
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3
Q

acetyl choline released from____ at ____

A

-released from presynatptic alpha-motor neuron at neuromuscular junction

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4
Q

acetylcholine diffuses across____ to bind to ____ in ___

A

acetylcholine diffuses across synaptic cleft to bind at nicotinic acetylcholine receptors in the muscle endlplate

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5
Q

nicotinic Ach receptors are

A

ligand-gated ion channels

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6
Q

Depolarization event at motor endplate is NOT

A

an action potential

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7
Q

action potenital occurs only if

A

enough miniature end plate potentials to summate to full-fledged end plate potential

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8
Q

Voltage gated Ca2+ channels in T-tubules closely associated with

A

calcium release channels in SR membrane which is why voltage-induced conformational change in T-tubule channel causes Ca2+ release channel to open

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9
Q

the linkage between voltage gated Ca2+ channels and Ca2+ release channels in SR is

A
  • mediated direct mechanical interactions between channels on T-tubule and SR
  • specifically by large cytoplasmic extension (foot process) of Ca2+ release channel
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10
Q

conformational change in troponin fx

A
  • pulls tropomyosin out of normal position on actin allowing for interactions between actin and myosin
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11
Q

myosin heads biding actin form

A

cross bridges

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12
Q

single step of movement down actin filament produced by

A

each cycle of ATP binding, hydrolysis, and phosphate release

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13
Q

cross-bridge cycle continues until

A

Ca2+ removed from cytoplasm by Ca2+-ATPase of SR membrane (SERCA) ultimately leading to Ca2+ release from troponin C -> tropomyosin returning to resting position -> blocking myosin bing sites on actin filaments

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14
Q

sequence of events in excitation-contraction coupling

A
  1. action potential
  2. increase cytosolic Ca2+ concentration
  3. Muscle contraction
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15
Q

summation

A
  • duration of contraction (twitch) long releative to duration exciting action potential so can initiate second action potential before first fully subsides causing second twitch to superimpose on residual tension first twitch this = summation
  • if frequency stimulation great enough individual twitches occur v close together in time and then are no longer distinguishable from each other
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16
Q

ATP use muscle contraction

A
  • Cross-bridge cycling
  • moving Ca2+ from cytoplasm back into SR
  • myocytes use ATP maintain and replenish membrane potentials
  • in exercise muscle use ATP can exceed 100x basal rate
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17
Q

ATP needed for contraction and relaxation

A

small ATP stores so have to regenerate ATP needed in contraction and relazation

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18
Q

energy pathways in muscle fiber

A
  1. stores ATP and phosphocreatinin
  2. Anerobic glycolysis
  3. Oxidative phosphorylation
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19
Q

Phosphocreatinin

A
  • most available pool energy= high energy bond phosphocratinine
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20
Q

phosphocreatinin produced by/ steps use

A
  1. transfer high energy phosphate from ATP to creatinine by creation kinase in mitochondria
  2. Phosphocreatinin diffuses from mitochondria -> major sites ATP utilization
  3. Phosphate transferred from phosphocreatinin to ADP
  4. dephosphorylated creatinine diffuses back to mitochondria where can be rephosphorylated
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21
Q

major sites ATP utilization

A
  • myofibrils
  • SR
  • Sarcolemma
22
Q

what allows for rapid regeneration ATP phosphocreatinin steps

A

phosphate transferee phosphocraatinin to ADP

23
Q

anaerobic glycoysis

A

produces ATP quickly to support muscle activity for few minutes but end products impair contractile fx

24
Q

end products anaerobic glycolysis

A
  • H+
  • lactate
  • both impair contractile fx
25
Q

oxidative phospohrylation

A

provides energy for muscle usage at intensities that can be sustained for longer than a few minutes

26
Q

fuels used by muscle fibers to produce ATP

A
  • main: carbohydrates and fats
  • small contributor to total energy production: metabolism of amino acid
  • selection of fuel depends on intensity and duration of exercise
27
Q

carbohydrates for fuel muscle fibers for ATP production in what forms

A
  • plasma glucose

- muscle glycogen

28
Q

fats for fuel muscle fibers for ATP production in what forms

A
  • free fatty acids

- muscle triglycerides

29
Q

fuel for high intensity exercise

A
  • glycogen stores= primary fuel
30
Q

fuel for low intensity exercise or long duration exercise

A
  • free fatty acid metabolism= major source
31
Q

affect of myosin and actin isoforms on cross-bridge cycling

A
  • isoforms affect speed of cross bridge cycling
  • some muscle fibers contract more quickly than others
  • speed contraction influences what metablic pathways used by cell
32
Q

2 main types muscle fiber

A
  1. type 1

2. type 2

33
Q

type 1 muscle fiber

A
  • slow
  • oxidative
  • fatiuge- resistant
  • postural muscles contain more type 1
  • shorten less rapidly than type 2?
34
Q

type 2 muscle fiber

A
  • fast
  • glycolytic
  • easily fatigued
  • fast-twitch shorten more rapidly than slow twitch (type 1?)
35
Q

virtually all muscles contain what muscle fibers

A

mix type 1 and type 2 allowing any muscle to be used in different activities with different mechanical and metabolic demands

36
Q

muscle fibers vary in what phenotypes

A

biochemical mechanical and metabolic phenotypes

37
Q

sarcomere

A

basic contractile unit skeletal muscle

38
Q

motor unit

A
  • basic functional unit of skeletal muscle
  • defined as single motor neuron and all the fibers it innervates
  • cells with in motor unit contract synchronously when motor neuron fires
  • vary in size
39
Q

small motor units

A

necessary for fine, precise movements

40
Q

muscles with large motor units

A

control course mvoements

41
Q

all fibers within motor unit=

A

same fiber type

42
Q

motor neuron pool

A

group of all motor neurons that innervate single muscle

43
Q

motor units and fasicles

A
  • motor units do not coincide with fascicular organization of muscle
  • each fasicle contains fibers belonging to many different motor units
44
Q

force generated by muscle depends on

A
  • degree of activation by nervous system
  • size of muscle
  • architecture of muscle (especially pinnation angle)
  • number actin-myosin cross-bridges formed
  • force generated by each cross-bridge
45
Q

muscles can generate increasing force how

A

frequency summation

multiple-fiber summation aka spatial summation

46
Q

frequency summation

A
  • at level of single fiber

- force increased by summing multiple twitches over time

47
Q

multiple-fiber summation or spatial summation

A
  • at level of whole muscle

- force can be increased by recruiting more motor units and summing contractions of multiple fibers

48
Q

muscle fiber activation during muscle activation

A
  1. brain recruited small motor units with slow oxidative fibers 1st
  2. excitatory input increases
  3. larger motor units containing fast-twitch fiber recruited -> increased force generation
49
Q

why can’t you sustain maximal tension for more than brief period of time

A

b/c fast twitch fibers fatigue more rapidly due to glycogen depeltion

50
Q

How are gradations in force accomplished at levels of force production lower than upper recruitment

A
  • changing number active motor units
  • changing firing rate in those that have been recruited
  • once all motor units have been recruited force can be increased only by increasing firing rate
51
Q

as more motor units recruited force

A

increases

52
Q

fluid and energetically efficient movements require

A

learning in order to achieve optimal recruitment patterns of motor units

Block 3 Up To Quiz 1 (24 decks)

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