Muscle Contraction and Sliding Filament Theory (Nursing)

00:01 Now switching gears, let's talk about how an contraction actually occurs.

00:07 In the sliding filament mechanism of our muscles, myosin is going to pull on actin, causing the thin filament to slide inward.

00:17 It's important to note that in a muscle contraction, neither the thin or the thick filament themselves shorten, but instead it is the arrangement of the thin and thick filaments in the sarcomere that changes.

00:34 After the myosin pulls on the actin the Z discs are going to move toward each other and the sarcomere is going to short and as a whole.

00:45 Thanks to the structural proteins, we can now transmit this force across the entire muscle and resulting in an entire or a whole muscle contraction.

00:57 So now let's discuss the contraction cycle.

01:00 During the contraction cycle, there are going to be several steps that occur that allow for the sliding filament mechanism to occur.

01:09 The first step in the contraction cycle involves the binding of calcium to the regulatory protein troponin.

01:17 This binding causes troponin to move the tropomyosin, so that the myosin head of the thick filament can bind to the actin or thin filament.

01:31 As well during this step, we also have ATP hydrolysis.

01:37 ATP will be converted to ADP and inorganic phosphate.

01:43 While this hydrolysis step happens the ADP and the inorganic phosphate remain attached to the myosin head.

01:51 And the myosin head is said to be energized or cocked into the ready position.

02:00 The next major step in the contraction cycle is going to be crossbridge formation.

02:06 During crossbridge formation, the now available myosin binding sites on the actin thin filament are bound by the myosin head.

02:18 In this step, the ADP and the inorganic phosphate are still attached.

02:25 Following this step, the ADP and the inorganic phosphate are removed from the myosin head.

02:32 This triggers the myosin to move or pull the thin filament past the thick filament toward the center of the sarcomere.

02:43 This step is referred to as the power stroke.

02:48 The final step in the contraction cycle involves that returning everything back to its original state.

02:56 We also refer to this as the crossbridge detachment step.

03:01 In this step, we are going to attach a new ATP molecule to the myosin head.

03:08 This causes or triggers the myosin head to detach from the actin thin filament.

03:16 And then we can start the process all over again.