00:02
So the question asks you to place the following events of muscle contraction in the correct sequence.
00:08
So the first one is sarcoplasmic reticulum releases calcium ions.
00:12
The second is that the z line slide closer together.
00:16
The third is a post -synaptic muscle cell is depolarized, triggering an action potential.
00:22
And number four is calcium concentrations decrease in the tropomyosin -troponin complex reforms over the myosin binding sites.
00:32
So let's break down what happens in a muscular contraction, right? so first, the muscle must be stimulated by an action potential.
00:43
Generally, the sarcomeres, the contractable units are in the off form, right? so actually the tropomycin troponin complex covers the binding sites and your muscles are relaxed.
00:56
So first we have to trigger the muscle cell with an action potential in order to turn the crossbridge cycle on.
01:05
And so here we would need the depolarized muscle cell, or the post -synaptic muscle cell to become depolarized, triggering an action potential.
01:16
That action potential spreads throughout the muscle cell, going down the t -tubules into the sarcoplasmic reticulum.
01:24
The sarcoplasmic reticulum, when depolarized, releases calcium into the sarcoplasm, right? so the cytoplasm of the muscle cell.
01:33
Now this calcium inside the muscle cell causes the tropomyocin troponin complex to move, opening up the myocin binding sites on actin.
01:43
This allows the crossbridge cycle to initiate as long as there's atp present...
