Skeletal Muscle Mechanics

isometric contraction

constant length with increasing tension

isotonic contraction

constant tension with decreasing length

active tension

tension developed by actin and myosin during contraction

why can muscles only be stretched to a certain length

a muscle that has been stretched to far will not have myofilament overlap

passive tension curve

caused by elasticity in muscles, does not involve actin myosin interaction

total tension curve

addition of passive and total tension curves

preload

sets passive tension and muscle length before contraction starts

afterload

felt by muscle after contraction begins

if active tension is greater than afterload

muscle will shorten during contraction

if active tension is less than afterload

the contraction will be purely isometric (no muscle shortening)

total load=

preload+afterload

muscle twitch

contraction due to one muscle action potential

what factors set twitch duration

Ca++release rate, Ca++ pump rate, myosin ATPase speed

what affects the amplitude of a muscle twitch

amount of Ca++ released by SR, myosin/actin overlap, myosin ATPase speed, # of motor units recruited

low frequency twitches

muscle has time to fully relax in between twitches

treppe

muscle has time to fully relax between twitches, but tension of muscles continually increases due to increased SR calcium release

medium frequency twitches

muscle doesnt have time to fully relax in between twitches, so they are summed up to increase tension

high frequency

tetanus, muscle contracts and stays contracted

fatigue of muscles is represented by

ATP depletion

muscle fiber types

type 1, type 2a, type 2x

type 1 muscle fiber

low ATP use, slow twitch, energy from oxidative phosphorylation, slowest to fatigue

type 2a muscle fiber

higher ATP use, fast twitch, energy from oxidative phosphorylation, slow to fatigue

type 2x muscle fibers

highest ATP use, fastest contraction speed, energy from glycolysis

rigor mortis

Ca in muscles cannot be pumped back into SR due to lack of ATP, muscles stiffen