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30 Cards in this Set

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isometric vs isotonic contraction
isometric - mnimal movement, measures foce generation

isotonic - movement, measures muscle shortening
can you determine how active force varies with muscle length in a whole muscle
not directly, because passive elements like CT sheaths, sarcolemma, and titin resist stretch or force when muscle is stretched beyond a critical length

so measure passive force of a muscle(force due to ct, etc) and measure total force at that length. Subtracting the two will give you the active force(just the force due to muscle contraction)
passive force curve, linear non linear?
non linear, CT elemtents are extended when stretched, are initially compliant then sharply resist futher extension
elastin vs collagen content in muscle and effect on passive force curve
the slower increase in resistive force is due to elastin which is more compliant, the sharp increase in resistance is due to collagen which is not compliant
see page 277 of muscle weakness module for information on isometric length force relationship
oh
at short muscle length which contributes more, active or passive force?
all total force is active, at long lengths, passive force contributes more and active force decreases because of decreased thin/thick filament overlap
pre-load vs afterload
preload = length of muscle, max F that can be developed

afterload = the resistance which the muscle must contract against
describe picking up a cup of coffee in terms of isometric and isotonic F
increase in isometric F to overcome the weight of the coffee

isotonic shortening(constant F) as you lift it to your mouth

isotonic relaxation as you put the cup down (contstant F)

isometric relaxation as the muscle relaxes since no load is present
length tension relationship
j
force velocity relationship
i
relationship between length/tension and force/velocity
m
three types of skeletal muscle fiber
slow twitch oxidative: brown
fast twitch A oxidative
fast twitch B fatigable: white
fenn effect
muscle utilizes more atp when it is shortening vs an isometric contraction
immediate recovery reactions of skeletal muscle when E is depleted
creatinine kinase, PCr +ADP = ATP + Cr

myokinase, 2ADP = ATP +AMP
secondary recovery reactions
req a finite period of time to be activated

glycolysis
ox phos
does training increase resistance to fatigue in fast twitch glycolytic fibers?
no, , but does increase amount of force generated
is smooth or skeletal myosin faster
skeletal is faster, smooth muscle myosin is sparse and slower
caldesmon
thin filaments of smooth muscle contain Ca,calmodulin,actin, myosin binding protein called caldesmon

it inhibits myosin ATPase activity
what are the critical differences between smooth and striated muscle?
smooth: NO troponin, instead thin filaments are made of actin tropomyosin, caldesmon and calponin,
classical sarcomeres as in striated muscle do not exist in smooth muscle
Force-length relationship in smooth muscle
force length relationship aka length-tension curve aka the preload curve thing

sliding filament explanation still holds for smooth muscle even though its sarcomeres are messed. Difference is smooth muscle can develop isometric force over a broader range of muscle lengths. Ie plateau(Lo) of the length tension curve in smooth muscle is extremely broad
Force-Velocity relationship
Vo = max velocity at 0 load(dep only on isoform!)
Fo = maximal force at 0 velocity

smooth muscle has a much lower velocity of shortening because of its isoform, but the maximal force that can be generated is still the same as skeletal
explain a smooth muscle AP
1) activation of a v-dependent inward Ca current, DHP R v-gated(not sensor)

2)activation of v-dep outward K AND inactivation of early transient inward Ca

3) plateau is a fight between sustained activation of v-dep Ca in and v-dep K out

4) repol = inactivation of Ca in and activation of Ca-dep outward K current
is an AP required for an increase in force?
not in smooth muscle, AP's can increase contraction, but smaller depols will cause a graded increase in Force

called electromechanical coupling
explain in more detail smooth muscle AP and Ca
calcium enters the cell through VOC's (DHP R, voltage operated channels) enough to initiate contraction, and can also enter through ROC's(receptor operated channels, ie IP3 DAG pathway that opens IP3R ca channel on SR!, ryanodine R are also present but we dont know what they do)
in a cardiac AP what source of Ca is responsible for the initial spike? what is responsible for the plateau?
spike = SR
plateau = EC Ca influx
describe smooth muscle activation of contraction
at resting levels smooth muscle is inactive, when AP hits Ca-Calmodulin complex binds MLC kinase, which then activates myosin allowing it to interact with actin and cross-cycle

smooth muscle is a true activation system, not disinhibition
what turns off smooth muscle contraction
MLC phosphatase deP's myosin light chain inactivating it

Critical concept: smooth muscle must be phosphorylated to interact with actin and produce force
latch state
maintenance of high levels of force during conditions of low or basal Ca levels and MLC phosphorylation, force is maintained by deP'd latchbridges
what causes greater force per Ca in smooth muscle, stimulation by an agonist (IP3 pathway) or membrane depol (DHP Ca channel)?
stimulation by an agonist,
RhoA
GTPbinding protein activates Rhokinase which can
1) p MLC and activate it
2) inhibit MLC phosphatase