Cardiac Muscle: Microscopic Anatomy (Nursing)

00:01 So recall that cardiac muscles are striated involuntary muscles.

00:07 Structurally, they have some similarities to our skeletal muscles but they also contain many differences.

00:15 Let's take a closer look at these differences.

00:20 Our cardiac muscles as I said are striated but they're also short, fat and interconnected.

00:30 Unlike our skeletal muscles which can contain multiple nuclei, our cardiac muscle fibers have one central nucleus and sometimes you might find two nuclei.

00:44 They also contain numerous large mitochondrial that can afford resistance to fatigue.

00:53 The rest of the volume of our cardiac muscle fibers is going to be composed of sarcomeres.

00:59 This is very similar to the sarcomeres that we find in our skeletal muscle fibers and include Z disc, A bands and I bands.

01:08 This contributes to the striation of our cardiac muscles.

01:16 The cardiac muscle cells have T-tubules like the skeletal muscles but the T-tubules here are wider and less numerous.

01:27 The T-tubules will enter the cell only once at the Z-disc.

01:33 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.

01:49 Please note that this image depicts a skeletal muscle fiber for comparison purposes only and is not a depiction of a cardiac muscle fibers.

02:03 So also in the heart, our cardiac muscle fibers had these structures known as intercalated discs.

02:11 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.

02:31 These junctions are going to allow ions to pass from cell to cell.

02:37 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.

03:01 Also in our skeletal fibers, outside of them, we have what are known as intercellular spaces.

03:08 These spaces contain connective tissue known as the endomysium.

03:14 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.