Skeletal Muscle Pt2

Question 1

Contraction of motor unit initiated from

Answer 1

CNS, occurs as all or noting twitch response

Question 2

Contraction of motor unit steps

Answer 2

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

Question 3

acetyl choline released from____ at ____

Answer 3

-released from presynatptic alpha-motor neuron at neuromuscular junction

Question 4

acetylcholine diffuses across____ to bind to ____ in ___

Answer 4

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

Question 5

nicotinic Ach receptors are

Answer 5

ligand-gated ion channels

Question 6

Depolarization event at motor endplate is NOT

Answer 6

an action potential

Question 7

action potenital occurs only if

Answer 7

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

Question 8

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

Answer 8

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

Question 9

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

Answer 9

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

Question 10

conformational change in troponin fx

Answer 10

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

Question 11

myosin heads biding actin form

Answer 11

cross bridges

Question 12

single step of movement down actin filament produced by

Answer 12

each cycle of ATP binding, hydrolysis, and phosphate release

Question 13

cross-bridge cycle continues until

Answer 13

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

Question 14

sequence of events in excitation-contraction coupling

Answer 14

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

Question 15

summation

Answer 15

• 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

Question 16

ATP use muscle contraction

Answer 16

• 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

Question 17

ATP needed for contraction and relaxation

Answer 17

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

Question 18

energy pathways in muscle fiber

Answer 18

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

Question 19

Phosphocreatinin

Answer 19

• most available pool energy= high energy bond phosphocratinine

Question 20

phosphocreatinin produced by/ steps use

Answer 20

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

Question 21

major sites ATP utilization

Answer 21

• myofibrils
• SR
• Sarcolemma

Question 22

what allows for rapid regeneration ATP phosphocreatinin steps

Answer 22

phosphate transferee phosphocraatinin to ADP

Question 23

anaerobic glycoysis

Answer 23

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

Question 24

end products anaerobic glycolysis

Answer 24

• H+
• lactate
• both impair contractile fx

Question 25

oxidative phospohrylation

Answer 25

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

Question 26

fuels used by muscle fibers to produce ATP

Answer 26

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

Question 27

carbohydrates for fuel muscle fibers for ATP production in what forms

Answer 27

- plasma glucose | - muscle glycogen

Question 28

fats for fuel muscle fibers for ATP production in what forms

Answer 28

- free fatty acids | - muscle triglycerides

Question 29

fuel for high intensity exercise

Answer 29

- glycogen stores= primary fuel

Question 30

fuel for low intensity exercise or long duration exercise

Answer 30

- free fatty acid metabolism= major source

Question 31

affect of myosin and actin isoforms on cross-bridge cycling

Answer 31

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

Question 32

2 main types muscle fiber

Answer 32

1. type 1 | 2. type 2

Question 33

type 1 muscle fiber

Answer 33

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

Question 34

type 2 muscle fiber

Answer 34

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

Question 35

virtually all muscles contain what muscle fibers

Answer 35

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

Question 36

muscle fibers vary in what phenotypes

Answer 36

biochemical mechanical and metabolic phenotypes

Question 37

sarcomere

Answer 37

basic contractile unit skeletal muscle

Question 38

motor unit

Answer 38

- 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

Question 39

small motor units

Answer 39

necessary for fine, precise movements

Question 40

muscles with large motor units

Answer 40

control course mvoements

Question 41

all fibers within motor unit=

Answer 41

same fiber type

Question 42

motor neuron pool

Answer 42

group of all motor neurons that innervate single muscle

Question 43

motor units and fasicles

Answer 43

- motor units do not coincide with fascicular organization of muscle - each fasicle contains fibers belonging to many different motor units

Question 44

force generated by muscle depends on

Answer 44

- 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

Question 45

muscles can generate increasing force how

Answer 45

frequency summation | multiple-fiber summation aka spatial summation

Question 46

frequency summation

Answer 46

- at level of single fiber | - force increased by summing multiple twitches over time

Question 47

multiple-fiber summation or spatial summation

Answer 47

- at level of whole muscle | - force can be increased by recruiting more motor units and summing contractions of multiple fibers

Question 48

muscle fiber activation during muscle activation

Answer 48

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

Question 49

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

Answer 49

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

Question 50

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

Answer 50

- 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

Question 51

as more motor units recruited force

Answer 51

increases

Question 52

fluid and energetically efficient movements require

Answer 52

learning in order to achieve optimal recruitment patterns of motor units