Skeletal Muscle Fibers: Histology (Nursing)

00:01 When we look at the microscopic anatomy of a muscle fiber, we find that the fibers can be divided into units known as sarcomeres.

00:11 Sarcomeres are going to extend from Z disc to the Z disc of the muscle fiber.

00:20 Inside of the Z disc or inside of the sarcomere you have several different zones.

00:27 The first zone or band is going to be the A band.

00:31 The A band is going to be composed of the entire length of the thick filament or the myosin filament found in the muscle fiber.

00:41 This area appears dark.

00:43 And when you're looking at the different parts of the striations.

00:48 Outside of the A band, you have two I bands.

00:52 The I bands are going to consist of the thin filaments or the actin filaments in the muscle fiber.

00:59 These are going to appear light in the striation.

01:04 Inside of the A band, we have the H zone.

01:07 The H zone is in the center of the A band.

01:11 And this is the zone that is going to change sizes during a muscular contraction.

01:17 Within the H zone, we have the M line.

01:22 Also we have the sarcoplasmic reticulum.

01:25 The sarcoplasmic reticulum is a structure that's going to be very important for a muscle contraction to occur.

01:32 This is going to be on the outside or covering the different myofibrils inside of the muscle fiber.

01:40 So now let's zoom in and take a closer look at the sarcoplasmic reticulum of the muscle fiber.

01:47 The sarcoplasmic reticulum wraps around each of the myofibrils of the muscle fiber.

01:55 At each end of the sarcoplasmic reticulum, you have an area known as the the terminal cisterna.

02:03 Also you have an area known as the T tubule.

02:07 The T tubule creates a trough that is between the different terminal cisterna.

02:15 Together with the two terminal cisterna and the central T tubule between them, you have a triad.

02:22 This unit is going to be very important for the contraction cycle which we will discuss shortly.

02:32 So, now let's look a little bit closer at the different proteins found in our muscles.

02:38 So as we've discussed, we have the contractile proteins, which include the myosin thick filaments, as well as the actin thin filaments.

02:48 These two proteins are going to interact with each other in order to allow the muscle fiber to shorten during a contraction.

02:57 Along with these, we have two regulatory proteins that play an important role in the muscle contraction as well.

03:05 These include troponin and tropomyosin.

03:11 Also, we have several structural proteins associated with the muscles.

03:15 We have titin, which is a structural protein that connects the Z disc to the M line of the sarcomere.

03:22 Alpha-actinin, which is the structural protein of Z disc that attaches to the actin molecules of thin filaments to the titin molecules.

03:32 Then, we have myomesin, which is the structural protein that forms the M line found in the H zone of the sarcomere.

03:41 We also have nebulin which is the structural protein that wraps around the entire length of each thin filament and anchors the thin filaments to the Z disc.

03:52 And finally, we have dystrophin.

03:54 Dystrophin is a structural protein that links the thin filaments of the sarcomere to the integral membrane proteins in the sarcolemma.

04:02 This is actually the protein that is affected by muscular dystrophy.