Flashcards in Skeletal Muscle Physiology Deck (96)
mechanical response to action potential
from AP initiation to cross bridge formation
-start of contraction
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
peak tension to complete relaxation
Ca2+ sequestering into the SR
total force generated?
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
muscle length constant
increase in tension, but no shortening
force production is equal to resistance
contraction occurs at constant load
-not really a constant force
length change occur
two phases of isotonic contraction
concentric and eccentric
muscle shortens as tension is produced
muscle lengthens as tension is produced
for isometric contractions
-force production depends on initial fiber length
muscle length influences tension devleopment by determining region of overlap between actin and myosin
tension prior to muscle contraction
increases as fiber is progressively lengthened because muscle becomes stiffer as it is distended
total tension - passive tension
cuased when cross-bridge cycling occurs in isometric contraction (fixed length)
when is active tension maximal?
near 100% of normal muscle length
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
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
normal resting length?
maximal overlap between actin and myosin filaments and maximal active tension
total tension = ?
passive + active tension
in isotonic contractions
shortening velocity decreases as load increases
**lighter loads can be lifted faster
determined primarily by maximum velocity of myosin ATPase enzyme
Vmax also varies with fiber type
smaller the load?
greater the shortening velocity
larger the load?
the lower the shortening velocity
what is contraction at zero velocity?
at a given fiber length?
there is a hyperbolic relationship between shortening velocity and load
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
longer the initial fiber length?
the larger the maximal load under zero-velocity conditions
aka isometric conditions
work = ?
load x displacement
measureable mechanical work
-only when muscle displaces a load
power = ?
maximal at intermediate lads
-where both F and v are moderate
zero load F= 0
maximum load v = 0
power also = ?
load x displacement / time
aka load x velocity (Fv)