So recall that cardiac muscles
are striated involuntary muscles.
Structurally, they have some similarities to our
skeletal muscles but they also contain many differences.
Let's take a closer look at these differences.
Our cardiac muscles as I said are striated
but they're also short, fat and interconnected.
Unlike our skeletal muscles
which can contain multiple nuclei,
our cardiac muscle fibers have one central
nucleus and sometimes you might find two nuclei.
They also contain numerous large mitochondrial
that can afford resistance to fatigue.
The rest of the volume of our cardiac muscle
fibers is going to be composed of sarcomeres.
This is very similar to the sarcomeres
that we find in our skeletal muscle fibers
and include Z disc, A bands and I bands.
This contributes to the striation of our cardiac muscles.
The cardiac muscle cells have
T-tubules like the skeletal muscles
but the T-tubules here are
wider and less numerous.
The T-tubules will enter the cell only once at the Z-disc.
Also, the sarcoplasmic reticulum of our cardiac muscle
cells is simpler than the sarcoplasmic reticulum
of the skeletal muscle cells and they do not contain
triads the way they do in our skeletal muscle fibers.
Please note that this image depicts a skeletal
muscle fiber for comparison purposes only
and is not a depiction of a cardiac muscle fibers.
So also in the heart, our cardiac muscle fibers
had these structures known as intercalated discs.
These discs are connecting junctions between
our cardiac cells that contain desmosomes
which are holding the cell together almost like velcro and
preventing the cells from separating during contraction,
and also just as importantly, gap junctions.
These junctions are going to
allow ions to pass from cell to cell.
Remember that we rely on ions in
order to maintain action potentials
and so these gap junctions allow for the
cells of the heart to be electrically coupled
so that the heart is going to function
as one big cell or a functional syncytium.
Also in our skeletal fibers, outside of them,
we have what are known as intercellular spaces.
These spaces contain connective
tissue known as the endomysium.
In the endomysium, we have several
capillaries and this is going to connect
the cardiac muscles to that cardiac skeleton or
valves giving the cells something to pull against,
something to actually resist against.