Skeletal Muscle Physiology Flashcards Preview

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Flashcards in Skeletal Muscle Physiology Deck (96)
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1

muscle twitch

mechanical response to action potential

2

latent period

from AP initiation to cross bridge formation
-start of contraction

3

contraction time

beginning of contraction to beginning of relaxation
-until peak tension

active sites exposed to when they begin to be covered up

when Ca2+ is high enough to keep active sites exposed

4

relaxation time

peak tension to complete relaxation

Ca2+ sequestering into the SR

5

total force generated?

tension
sum of forces independently produced by many cycling cross-bridges

can vary with:
initial length of muscle fiber
pattern or frequency of muscle fiber stimulation

6

isometric contraction

muscle length constant
increase in tension, but no shortening

force production is equal to resistance

7

isotonic contraction

contraction occurs at constant load
-not really a constant force

length change occur

8

two phases of isotonic contraction

concentric and eccentric

9

concentric phase

muscle shortens as tension is produced

10

eccentric phase

muscle lengthens as tension is produced

11

length-tension relationship

for isometric contractions
-force production depends on initial fiber length

muscle length influences tension devleopment by determining region of overlap between actin and myosin

12

passive tension

tension prior to muscle contraction

increases as fiber is progressively lengthened because muscle becomes stiffer as it is distended

13

active tension

total tension - passive tension

cuased when cross-bridge cycling occurs in isometric contraction (fixed length)

14

when is active tension maximal?

near 100% of normal muscle length

15

what happens with increased fiber length?

ends of actin are pulled away from each other

greater than 150% - ends of actin are pulled beyond myosin

no interaction/overlaps occur and therefore no development of tension

16

what happens with decreased fiber length?

actin and myosin increase overlap
ends of actin filaments are pushed toward eachother

-tension can develop depending on degree of overlap

shortening to less than 70-85% of resting length
-opposing actin filaments slide over one another and hit Z disks

17

normal resting length?

of sarcomere

maximal overlap between actin and myosin filaments and maximal active tension

18

total tension = ?

passive + active tension

19

force-velocity relationship

in isotonic contractions

shortening velocity decreases as load increases

**lighter loads can be lifted faster

20

maximum velocity?

determined primarily by maximum velocity of myosin ATPase enzyme

Vmax also varies with fiber type

21

smaller the load?

greater the shortening velocity

22

larger the load?

the lower the shortening velocity

23

what is contraction at zero velocity?

ISOMETRIC!

24

at a given fiber length?

there is a hyperbolic relationship between shortening velocity and load

25

what does maximal velocity depend on?

maximal rate of cross-bridge turnover
-not on initial overlap of thin and thick filaments

therefore, it is independent of length

26

longer the initial fiber length?

the larger the maximal load under zero-velocity conditions

aka isometric conditions

27

work = ?

load x displacement

measureable mechanical work
-only when muscle displaces a load

28

power = ?

work/time

maximal at intermediate lads
-where both F and v are moderate

zero load F= 0
maximum load v = 0

29

power also = ?

load x displacement / time

aka load x velocity (Fv)

30

frequency summation?

tension of single fiber can be summed if APs fire rapidly

aka twitch summation

repetitive stimulation leads to increased tension