muscle tension

pull

tension produced when muscle cells contract

resistance

tension must overcome the load to produce movement

cycling rate

number of power strokes per second. what the speed of shortening is dependent on

the duration of a contraction depends on…

• duration of neutral stimulus

• presence of free Ca ions in cytosol

• availability of ATP

relaxation

as Ca is pumped back into SR and Ca concentration in cytosol falls,

• Ca detaches from troponin

• troponin returns to original position

• active sites are covered by tropomyosin and the contraction ends

muscle contraction initiation 1

ACh is released at MJ and binds to ACh receptors on sarcolemma

muscle contraction initiation 2

AP is generated and spreads across the membrane surface of the muscle fiber and along the T tubules

muscle contraction initiation 3

sarcoplasmic reticulum releases stored Ca

muscle contraction initiation 4

Ca bind to troponin, exposing the active sites on thin filaments. cross bridges form when myosin heads bind to the active sites

muscle contraction initiation 5

contraction cycle begins as repeated cycles of cross bridge binding, pivoting, and detachment occur (all powered by ATP)

muscle contraction end 6

ACh is broken down by acetylcholinesterase (AChE), ending AP generation

muscle contraction end 7

Ca are reabsorbed and their concentration in cytosol decreases

muscle contraction end 8

without Ca, tropomyosin return to normal position and active sites are covered again

muscle contraction end 9

without cross bridge formation, contraction ends

muscle contraction end 10

muscle returns passively to its resting length

rigor mortis

fixed muscular contraction after death. results when ATP runs out and ion pumps stop working, or from Ca build up in cytosol