So the muscle contractions in our cardiac muscle
is preceded by a depolarising action potential
just as it is in our skeletal muscles.
Also, the depolarization wave is going to travel down T-tubules
causing the sarcoplasmic reticulum to release calcium ions.
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.
This is very similar to the actions
that we see in our skeletal muscle fibers.
But there are also some differences between
the skeletal muscles and the cardiac muscles
when it comes to actually contracting.
So first, some of our cardiac muscle cells are
self-excitable, we do not see this in skeletal muscles.
There two different types of
myocytes or muscle cells in the heart.
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.
These cells are important because they are going
to initiate the depolarization of the entire heart.
Unlike skeletal muscle fibers, these pacemaker cells do not
actually need the nervous system in order to be stimulated.
As I said before, the heart is gonna contract
as a single unit or a functional syncytium.
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.
Contraction of all over cardiomyocytes
ensures an effective pumping action
unlike with the skeletal muscle
fibers which contract independently.
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.
In the cardiac muscle fibers, depolarizing is going to
open the slow calcium channels found in the sarcolemma.
This is going to allow those calcium ions to enter the cell.
Extracellular calcium is then gonna cause the sarcoplasmic
reticulum to release that intracellular calcium.
Skeletal muscles do not have this process and they do not use
extracellular calcium ions in their process of depolarization.
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.
And because of this, we can not get to tetanic
contractions or contractions that kind of go up and down.
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.
Another difference between our cardiac muscles and
skeletal muscles is the absolute dependence on oxygen
of our cardiac muscle fibers.
The cardiac muscles have more
mitochondria than the skeletal muscles
because of this greater dependent on oxygen.
The cardiac muscle fibers can not function
without oxygen while skeletal muscles can.
In the absence of oxygen, our skeletal muscles can go
through fermentation, cardiac muscle fibers cannot.
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.