Cardiac and Skeletal Muscle (Nursing)

00:01 So the muscle contractions in our cardiac muscle is preceded by a depolarising action potential just as it is in our skeletal muscles.

00:13 Also, the depolarization wave is going to travel down T-tubules causing the sarcoplasmic reticulum to release calcium ions.

00:24 Excitation and contraction coupling is going to occur just as it does in the skeletal muscle fibers and calcium is going to bind the molecule troponin causing our filaments to slide.

00:39 This is very similar to the actions that we see in our skeletal muscle fibers.

00:46 But there are also some differences between the skeletal muscles and the cardiac muscles when it comes to actually contracting.

00:54 So first, some of our cardiac muscle cells are self-excitable, we do not see this in skeletal muscles.

01:03 There two different types of myocytes or muscle cells in the heart.

01:08 We have the contractile cells which are going to be responsible for the actual contraction and then we have non-contractile cells that are going to spontaneously depolarize known as our pacemaker cells.

01:24 These cells are important because they are going to initiate the depolarization of the entire heart.

01:32 Unlike skeletal muscle fibers, these pacemaker cells do not actually need the nervous system in order to be stimulated.

01:44 As I said before, the heart is gonna contract as a single unit or a functional syncytium.

01:52 All of our cardiomyocytes are gonna contract as a unit, it's either and all-or-none process so either all of them contract or none of them contract.

02:05 Contraction of all over cardiomyocytes ensures an effective pumping action unlike with the skeletal muscle fibers which contract independently.

02:20 So during this process, we get an influx of calcium ions from our extracellular fluid which is going to trigger a release from the sarcoplasmic reticulum.

02:34 In the cardiac muscle fibers, depolarizing is going to open the slow calcium channels found in the sarcolemma.

02:43 This is going to allow those calcium ions to enter the cell.

02:48 Extracellular calcium is then gonna cause the sarcoplasmic reticulum to release that intracellular calcium.

02:57 Skeletal muscles do not have this process and they do not use extracellular calcium ions in their process of depolarization.

03:09 Another thing is that cardiac muscles have a longer absolute refractory period compared to that of skeletal muscles because the absolute refractory period is long, it's almost as long as the heart contraction itself.

03:28 And because of this, we can not get to tetanic contractions or contractions that kind of go up and down.

03:37 This allows the heart to completely relax and fill as needed so that it can efficiently pump blood to the rest of the body or to the pulmonary circuit.

03:51 Another difference between our cardiac muscles and skeletal muscles is the absolute dependence on oxygen of our cardiac muscle fibers.

04:01 The cardiac muscles have more mitochondria than the skeletal muscles because of this greater dependent on oxygen.

04:10 The cardiac muscle fibers can not function without oxygen while skeletal muscles can.

04:18 Both types of tissue can also use other fuel sources and cardiac muscle fibers are more adaptable to other fuels including lactic acid but regardless of what fuel is used, oxygen must be present.