6. Muscle Flashcards
What are the sarcomeres?
Under the light microscope, a sarcomere is composed of a dark bend (A), flanked by light bands (I). Under the electron microscope a Z line is well observable and appears to bisect the I band. The Z-lines define the borders of a sarcomere, thus a sarcomere is composed of one A band and flanked by ½ of two I bands.
What is the distinction between myofilaments, myofibrils, and muscle fibers?
Myofilaments are polymers of either actin (thin filament) or myosin (thick filament). Actin and myosin are organized into myofibrils, and multiple myofibrils make up a muscle fiber.
What are the differences between the tendon and skeletal muscle?
Most cells of the tendon (tendinocytes) are compressed by the extracellular collagen bundles, only the nuclei are visible, and appear more flattened than muscle fiber’s nuclei. At certain locations the striation of the muscle fibers is observable. Collagen fibers are not striated under the light microscope.
Q6: What is the location of the cardiac muscle fiber nucleus?
Central, one or two per cell.
Q7: What are the characteristics of the nucleus in smooth muscle?
Most display mixture of heterochromatin and euchromatin, a difference from fibroblasts that are mostly heterochromatic. Many have “corkscrew” shape, reflecting a contracted state of the cell.Elongated shape and central location.
Why do smooth muscle cells in cross sections have different diameters?
They have spindle shape, tapering ends. As they interdigitate, different diameters are revealed in the plane of section.
Are sarcomeres present in smooth muscle?
No. Bundles of myofilaments are arranged as a network.
Q11: What are the distinguishing features of the skeletal and smooth muscle types?
The skeletal muscle fibers are considerably larger, and appear as rounded polygons, the nuclei are peripheral, at high magnification the myofibrils may appear separated, an artifact of fixation. Many of the smooth muscle cells do not appear to have nuclei, as the plane of section is through their tapering ends. When visible it appears central in the cytoplasm.
what stain can be used for cardiac muscle? What does it look like?
Weigert stain. reference slide 219 of cardiac muscle
what do myocytes look like for patients with hypertension?
In patients with hypertension, the cardiac myocytes undergo hypertrophy (enlarge) to contract more forcefully against the resistance of the blood vessels. These cells can be recognized by their large “boxcar” nuclei.
Sarcomere shortening in striated muscle is associated with
A. shortening of the thick (myosin) filaments
B. shortening of the thin (actin) filaments
C. reduction in width of the A band
D. reduction in width of the I band
E. shortening of the nebulin molecule
D-The I band represents that portion of the actin-containing thin filaments that is not overlapping with the thick filaments. As muscle contraction proceeds, the amount of overlap of thick and thin filaments increases and hence the width of the I band decreases. Hence, this is the correct answer.
