tension production in muscle fibers

the amount of tension produced depends on…

number of power strokes performed at cross bridge

if the number of contracting sarcomeres in a muscle fiber is fixed, then a muscle fiber is..

either producing tension or is relaxed

the amount of tension produced in a muscle fiber depends on…

• fiber’s resting length at time of stimulation

• frequency of stimulation

length tension relationship

tension produced by a muscle relates to the length of the sarcomeres. amount of tension produced depends on:

• # of power strokes performed by cross bridges

• amount of overlap between thick and thin filaments

optimal resting length

length where zone of overlap is large and produces maximum tension

increased sarcomere length

length where zone of overlap is decreased and tension production decreases

decreased sarcomere length

thin filaments extend across center of sarcomere and tension production decreases. when thick filaments contact Z line, sarcomere cannot shorten and tension cannot be produced

twicth contraction

a single neural stimulation produces a single contraction-relaxation sequence. lasts 7-100 msec; time varies on muscle location

eye muscles have ___ twitch contractions

faster

lower leg muscles have ___ twitch contractions

longer/slower

myogram

a graph showing tension development in muscle fibers

3 phases of a single twitch

1. latent period

2. contraction phase

3. relaxation phase

latent period

AP moves across sarcolemma, SR releases Ca. no tension produced in the muscle fiber

contraction phase

Ca bind to troponin and cross bridges form; sliding filament theory occurs. tension builds to a peak

relaxation phase

Ca pumped back into SR, cross bridges detach, active sites on actin are covered by tropomyosin, and tension in muscle fibers decreases

treppe

stair-step increase in tension caused by repeated stimulations immediately after relaxation phase. stimulus frequency of <50/sec; produces a series of contractions with increasing tension. typically seen in cardiac muscles rather than skeletal muscle

wave summation

increasing tension due to summation of twitches caused by repeated stimulations before end of relaxation phase. stimulus frequency of >50/sec

tetanus

maximum tension

incomplete tetanus

muscle produces near-maximum tension, caused by rapid cycles of contraction and relaxation

complete tetanus

higher stimulation frequency eliminates relaxation phase. muscle is in continuous contraction, and all potential cross bridges form