Department Homepage‎ > ‎First year‎ > ‎FAQs‎ > ‎

Muscular tissue

Drs, plz, what are the coverings of the muscle fibers?

Individual muscle fibers are ensheathed by the endomysium that contains the basal lamina (external lamina). The basal lamina consists of two layers, the lamina densa and lamina rara.
The muscle fibers arranged into bundles, the bundles are surrounded by connective tissue "perimysium". The whole muscle is surrounded by "epimysrium"

I can't imagine the triad system, thanks

Triad in skeletal muscle (Terminal Cisternae---T-Tubule---Terminal Cisternae).
Terminal cisternae are the enlarged ends of sarcoplasmic reticulum which act as Ca reservoir.
Transverse Tubule (t-tubule): Connects sarcolemma(cell membrane) with Sarcoplasmic Reticulum.
It occurs at A-I junction. 

What is "diad"?

The tubular system in cardiac muscle fibers:
T-tubules occur at Z line rather than A-I junction, cardiac T-tubles form diad with one expanded cisterna.

What are the types of skeletal muscle fibers, and what are the differences?

The human body has three major types of skeletal muscle fibers: fast fibers, slow fibers, and intermediate fibers.

Fast Fibers Most of the skeletal muscle fibers in the body are called fast fibers, because they can contract in 0.01 sec or less after stimulation. Fast fibers are large in diameter; they contain densely packed mofibrils, large glycogen reserves, and relatively few mitochondria. The tension produced by a muscle fiber is directly proportional to the number of sarcomeres, so muscles dominated by fast fibers produce powerful contractions. However, fast fibers fatigue rapidly because their contractions use ATP in massive amounts, so prolonged activity is supported primarily by anaerobic metabolism. Several other names are used to refer to these muscle fibers, including white muscle fibers, fast-twitch glycolytic fibers, and Type II-A fibers.

Slow Fibers Slow fibers are only about half the diameter of fast fibers and take three times as long to contract after stimulation. Slow fibers are specialized to enable them to continue contracting for extended periods, long after a fast muscle would have become fatigued. The most important specializations improve mitochondrial performance. Slow muscle tissue contains a more extensive network of capillaries than is typical of fast muscle tissue and so has a dramatically higher oxygen supply. In addition, slow fibers contain the red pigment myoglobin . This globular protein is structurally related to hemoglobin, the oxygen-carrying pigment in blood. Both myoglobin and hemoglobin are red pigments that reversibly bind oxygen molecules. Although other muscle fiber types contain small amounts of myoglobin, it is most abundant in slow fibers. As a result, resting slow fibers contain substantial oxygen reserves that can be mobilized during a contraction. Because slow fibers have both an extensive capillary supply and a high concentration of myoglobin, skeletal muscles dominated by slow fibers are dark red. They are also known as red muscle fibers, slow-twitch oxidative fibers, and Type I fibers.

With oxygen reserves and a more efficient blood supply, the mitochondria of slow fibers can contribute more ATP during contraction. Thus, slow fibers are less dependent on anaerobic metabolism than are fast fibers. Some of the mitochondrial energy production involves the breakdown of stored lipids rather than glycogen, so glycogen reserves of slow fibers are smaller than those of fast fibers. Slow fibers also contain more mitochondria than do fast fibers. 

Intermediate Fibers The properties of intermediate fibers are intermediate between those of fast fibers and slow fibers. In appearance, intermediate fibers most closely resemble fast fibers, for they contain little myoglobin and are relatively pale. They have a more extensive capillary network around them, however, and are more resistant to fatigue than are fast fibers. Intermediate fibers are also known as fast-twitch oxidative fibers and Type II-B fibers.

Why do smooth muscle fibers appear having different diameters in TS?

In the cross-section see how some cells are cut in the center and contain nuclei whereas other cells are cut at their tips

Plz dr, I can't understand (atrial natriuretic polypeptide ) in cardiac muscle thanks in advance

ANP is a hormone secreted by the cells of the atrial muscles involved in regulation of the electrolyte concentration of EC fluid.

Fibrous skeleton of the heart, I can't imagine it, thanks

The fibrous skeleton of the heart, dense fibrous connective tissue, between the junctions between the 2 atria and 2 ventricles. Cardiac muscles and valves are attached to the fibrous skeleton

The nucleus of the smooth muscle takes a characteristic cork-screw appearence during contraction?..Can you please explain it more Dr.?

Shortening of the cell during contraction leads to shortening of the space to be occupied by the nucleus giving the cork screw appearance

Drs please, I want a picture explaining caveolae in smooth muscle.