Contractile mechanics Flashcards
what is the difference between unfused and fused tetanus
unfused = caused by repeated stimulation pulses at higher frequencies that results in twitches summating
fused = caused by repeated stimulation pulses at higher frequencies than unfused that results in fusion - smoothing out of force
what is the differences in twitches/tetanus in the different fibre types
fast
- activates and deactivates sooner
- can reach higher peak force
- requires higehr stimulation frequencies in order to reach fused tetanus
slow
- activates and deactivates slower
- requires lower stimulation frequencies to reach fused tetanus
what does the amount of force a sarcomere can produce depend on
depends on the amount of overlap between actin and myosin filaments
(active force-length relationship - due to sliding filaments)
- changes depending on sarcomere length
what is the average resting sarcomere length
2-2.2 um
are all the sarcomere lengths the same in whole muscle
- what does this result in
no - heterogenous (sarcomere non - uniformity)
results in smoothing of the whole muscle force length relationship (averaging effect of force - length relationship)
what occurs during the ascending limb of the force length relationship
length and force increases
- as force increases, length increases (cross bridge cycling)
what occurs during the descending limb of the force length relationship
as length increases past the plateau region, force decreases
- not enough overlap for cross bridges to form
why do we normalise force and length
to allow comparison across muscles of different sizes
what is the optimal length vs normalised muscle length
optimal length = length where max isometric force occurs
normalised length = all values divided by optimal length value
what is the optimal force vs normalised muscle force
optimal force = max isometric force
normalised = all values divided by optimal force value
what causes passive forces at the sarcomere level
primarily due to titin (protein)
- resistive force - muscle wants to recoil
- titin stretches like a spring and produces recoil force to move it back to a shorter length
what causes passive forces at the whole muscle level
due to ECM
- endo, peri, and epimysium
- also other structures
how is total muscle force found
given by adding the passive and active forces
what is the path of total force on a graph
total force increases (active force increases)
dips and decreases (between active and passive max)
increases again after (passive force increases)
what does the max shortening velocity depend on
depends on fibre type properties
- faster fibres / muscle shave faster shortening velocities
when can muscles produce force (concentric vs eccentric)
muscles can only produce force in concentric movement
in eccentric:
- muscle is still producing force to shorten but the force to lengthen over rides it so the net movement is lengthening
what is the relationship between shortening velocity and force production
faster the muscle shortens, the lower the force will be
- max shortening veleocity produces barely any force
- depends on fibre type
what is the huxley muscle model
based on dynamics of a cross bridge
limitations
- don’t have good descriptions of everything included in the model
- don’t account for things outside the fibre (muscle shape, function, volume)
what is the geometric muscle model
useful in understanding importance of muscel shape change and affect on force
can account for different shape change factors (constant volume, thickness, and area)
what is the 3D continuum model
accounts for volume, ECM, and 3D shape
can account for non uniformity (understand more complexity)
what is the basis of a hill type muscle model
the model muscle is a scaled up single muscle fibre
consists of 3 elements:
1. CE = contractile element
2. PEE = parallel elastic element
3. SEE = series elastic element
what is the difference between a series and parallel arrangement
series = all components are equal to each other
parallel = all components add together
what is the contractile element and what is it combined with
contractile element = active muscle force
in parallel with parallel elastic element
(added together)
what is the parallel elastic element and what is it combined with
PEE = passive muscle force
in parallel with contractile element
(added together)
in series with series elastic element
(equal to)
what is the series elastic element and what is it combined with
SEE = tendon force
in series with both the contractile element and the parallel elastic element (total muscle force)
(equal to)
what is the activation component
scales the active force
1 = max force contraction
everything below 1 = submax contraction
what does muscle force depend on
contraction history
- previous active lengthening and shortening
what is the muscle force response following active lengthening
force enhancement
(increase in force)
what is the muscle force response following active shortening
force depression
(decreases)
why does force enhancement occur
likely due to the behaviour of titin
