Cardiac and Smooth Muscle (Nursing)

00:01 So now let's switch gears again and discuss different types of muscles.

00:06 So we spent a lot of time discussing the skeletal muscles, but recall there are two other muscle tissues in the body.

00:14 The first one we'll discuss is the cardiac muscles.

00:18 So the cardiac muscles are very similar to the skeletal muscles and that they are both striated.

00:25 However, there are some key differences between the two.

00:29 First, this cardiac muscles have only one nucleus, whereas, the skeletal muscle fibers can often have several nuclei per fiber.

00:40 Also, cardiac muscle cells contain structures known as intercalated discs.

00:46 Intercalated discs are where the two cardiac muscles are going to join.

00:51 They are joined together by desmosome and gap junctions.

00:56 Recall we learned about these different types of cell junctions in a previous lecture.

01:01 These allow the muscle action potentials to spread from one muscle fiber to another.

01:09 So speaking of gap junctions.

01:11 The gap junctions are very interesting as they allow the heart cells to actually function as a syncytium.

01:19 In other words, the heart is going to act like one big cell, even though it is made up of thousands of cells.

01:29 So an interesting fact about cardiac muscle cells is that they actually have more mitochondria and their contractions last 10 to 15 times longer than that of the skeletal muscle contraction.

01:44 So the next type of muscle tissue in the body is the smooth muscle tissue.

01:49 Smooth muscles often line most of our visceral organs.

01:54 Smooth muscles look very different than that of the cardiac and the skeletal muscles.

02:01 They are shaped different, whereas thick in the middle and tapered toward the ends.

02:06 And also, unlike skeletal muscles and cardiac muscles, smooth muscles do not contain striations.

02:15 Also, smooth muscles can be arranged as single-units or can act as multi-unit fibers.

02:23 Smooth muscle contractions start more slowly, but last longer than that of skeletal and cardiac muscle contractions.

02:33 The contractile proteins found in smooth muscles are also not organized into sarcomeres like they are in skeletal and cardiac muscles.

02:44 In these type of muscles because of the arrangement of the contractile proteins, when smooth muscles contract, they contract and a corkscrew motion instead of a shortening motion.

02:59 Also in smooth muscles, they use different regulatory proteins.

03:04 Whereas, in the skeletal muscles and the cardiac muscles, we're going to use troponin and tropomyosin.

03:11 In smooth muscles, the regulatory proteins include calmodulin and myosin light chain kinase.

03:19 Also, smooth muscles can shorten and stretch to a much greater degree than that of skeletal and cardiac muscles.

03:28 And finally, smooth muscle fibers shorten in response to stretch.