Muscle Mechanics Flashcards
describe the temporal relation between skeletal action potential, calcium and tension.
action potential comes first, followed by calcium increase and tension. there is a slight gap between each of the phases
what is an isometric contraction?
when skeletal muscle contracts and stays the same length because it is attached to two immovable objects
how much work is done in an isomeric contraction? how much power?
none of either because there was no distance moved
in what instances are isometric contractions involved?
maintaining posture.
also used to experiment with muscle properties
how does an isometric contraction occur with the shortening of contractile units?
the elastic element of the muscle (tendon) elongates by an equal distance to keep the length of the muscle fiber constant
what is an isotonic contraction?
a contraction associated with a change in length
what are most coordinated movements of the body involving?
isometric and isotonic combinations of contractions
isometric contractions maintain posture while isotonic contractions produce movement
how is isotonic twitch measured?
by attaching the muscle to a movable load
describe the force of an isotonic twitch.
what will create a different tension curve?
the force shows a plateau during which the force is constant
a different curve will occur with a change in load
how does a greater load affect the tension curve of an isotonic twitch?
higher plateau and greater time lag between stimuli ad the start of muscle shortening
what occurs when the load exceeds the amount of force that the isotonic muscle can generate?
an isometric twitch results
what is the series elastic element?
a rubber band like tendon that includes all of the elasticity that is in the system
at what point does the load begin to move in an isotonic twitch?
when the tension builds up to the point it equals or slightly exceeds the load
what happens to the tension once the load begins to move?
the tension becomes constant
what are the four stages of an isotonic twitch?
1) isometric tension development
2) isotonic shortening at constant tension
3) isotonic relaxation- return to initial length at constant tension
4) isometric relaxation
what is the formula for work? what is the formula for power?
work=tension x distance shortened
power= work/time
what is the initial velocity of shortening? what is the rate of development of tension?
the initial slope of the shortening curve
the slope of the tension vs time curve
what is the rate of tension development a function of?
the active properties of the muscle and the passive properties of the tissue (like tendons)
when is the velocity of shortening maximal?
at the beginning of shortening
as the load increases for an isotonic twitch, what three aspects of muscle shortening change?
initial velocity of shortening decreases, the amount of shortening decreases and the duration of shortening increases
at what point is the maximal amount of tension for the initial length?
when the muscle cannot lift the weight at all
what is a measure of strength or health of a heart?
the maximal rate of tension development during isovolumic contraction
what are some effects in the distance shortened vs time plot with increasing isotonically with increasing loads?
latent period increases, duration of shortening decreases and the velocity of shortening decreases
at what condition is Vmax experienced for an isotonic contraction? what is Vmax a function of?
under zero load
a function of myosin ATP ase in varying muscle types
what is Po?
the maximal isometric tension that can be generated at a given initial length and a state of contractility (when the muscle can not lift, the largest tension)
what is Po a function of?
the number of cross bridges that can be formed
larger muscle have larger number of cross bridges
how can Po for a skeletal muscle increase?
frequency modulation, recruitment of additional motor units and with initial lengths closer to the optimal initial length
how can Po for cardiac muscle increase?
increased initial length, and by increased contractility (not by recruitment because all cells already contract)
when do myofibers produce maximum work and power?
at intermediate loads
why is velocity of shortening an important concept?
because different types of fibers differ in their velocity of shortening
what are preload and afterload?
preload is the load required to stretch a muscle from its resting length
afterload is equivalent to the total tension
at what length do muscles normally operate?
at 100-115% of resting length
what comprises the total load of a muscle?
the preload and afterload
how was the length tension diagram devised?
by measuring isometric twitches at varied lengths
what are the characteristics of tension for an isometric skeletal muscle contraction?
tension develps at constant length to maximal tension for that particular initial length and then decreases to 0g at constant length
how many newtons are in a kg of force?
9.8N
