Block IV: Skeletal muscle

Question 1

What are the types of muscle?

Answer 1

1. Skeletal : visceral striated (voluntary striated)
2. cardiac muscle (involuntary striated)
3. smooth muscle (involuntary non-striated)

Question 2

what is the main function of muscles?

Answer 2

movement or tension

Question 3

main functions of skeletal muscle?

Answer 3

(also visceral striated muscle)- movements & tension in the skeletal system/ tongue, some eye muscles, voluntary sphincters.

Question 4

main functions of cardiac muscle?

Answer 4

heart beat

Question 5

main functions of smooth muscle

Answer 5

walls of tubular organs (digestive/respiratory) and some solid organs

Question 6

identify

Answer 6

skeletal muscle

Question 7

identify

Answer 7

cardiac muscle

Question 8

identify

Answer 8

smooth muscle

Question 9

What are some histological characteristics of skeletal muscle?

Answer 9

1. striated: cross-striations
2. large diameter fibers: 30- 50 nuclear diameters across. (The terms fiber and skeletal muscle cell are equivalent in this case)
3. peripheral location of nuclei: vs central for cardiac & smooth
4. multiple nuclei: vs. single nucleus cardiac & smooth
5. physical syncytium: arises from fusion of myoblasts (200-300
   myoblasts) during embryonic development

Question 10

identify

Answer 10

cross-section through skeletal muscle

Question 11

identify

Answer 11

longitudinal section of skeletal muscle with inset showing cross-striation pattern

Question 12

identify

Answer 12

Low magnification micrograph of cross section of skeletal muscle showing the perimysium and Endomysium

Question 13

identify

Answer 13

high magnification micrograph of cross-section skeletal muscle showing muscle fibers surrounded by endomysium CT

Question 14

identify

Answer 14

Scanning EM of endomysium layer after removal of muscle cell

Question 15

What are the connective tissues of skeletal muscle?

Answer 15

1. Epimysium
2. Perimysium
3. Edomysium

Question 16

What is the epimysium?

Answer 16

Continuous with tendons, and forms a sheath on the surface of
muscle (outer layer) surrounds entire muscle

Question 17

What is the Perimysium?

Answer 17

Surrounds small bundles or fasicles of muscle fibers.

Question 18

What is the endomysium?

Answer 18

fine layer of reticular fibers surrounding each fiber/skeletal muscle cell.

Question 19

What is a sarcomere?

Answer 19

Is the repeating structural unit of skeletal muscle that gives
the striated appearance.

Question 20

What are the divisions of the sarcomere?

Answer 20

1. Z-bands -dense-staining thin lines
2. I-bands - lighter staining regions adjacent to Z-bands
3. A-band – broad dense staining region at center of sarcomere
4. H-band -lighter staining zone at center of A-band

Question 21

identify the regions

Answer 21

Question 22

In what layer are the small capillaries and small nerves serving the individual sekeletal muscles cells/fibers?

Answer 22

endomysium

Question 23

How does the sarcomere appear in TEM?

Answer 23

Within the electron microscope (TEM) it can be seen that the sarcomere consists in large part of interdigitating arrays of actincontaining thin filaments (orange) attached to Z-band and myosin-containing thick filaments (yellow) and their associated
proteins

Question 24

What are the contents of the Z-bands?

Answer 24

contain alpha-actinin that crosslinks the thin filaments of
adjacent sarcomeres

Question 25

What are the contents of the I-bands?

Answer 25

contain actincontaining thin filaments attaching to Z-band

Question 26

What are the contents of the A-band?

Answer 26

myosin-containing thick filaments (overlapping with thin filaments at ends)

Question 27

What are the contents of the M-band?

Answer 27

3-5 bands - strut-like connections between thick filaments at center of A-band formed by proteins myomysium, M-protein, and obscurin.

Question 28

What are the contents of the H-band?

Answer 28

Light-staining region at center of A-band where have only thick filaments (non-overlap region thick & thin)

Question 29

What are myofibrils?

Answer 29

The myofibril is a linear array of sarcomeres end to end within the cytoplasm of the muscle cell. Hundreds of myofibrils are present in cytoplasm

Question 30

WHta separates the myofibrils and how do they appear?

Answer 30

The myofibrils are separated by regions of cytoplasm with mitochondria, glycogen, and membranes. Appear as dots in CX of muscle fiber in light microscope

Question 31

identify

Answer 31

EM of skeletal muscle showing Myofibrils

Question 32

identify

Answer 32

High magnification micrograph of cross-section through skeletal muscle fibers showing stippled appearance due to sectioned myofibrils

Question 33

identify

Answer 33

EM of cross-section through skeletal muscle fiber showing myofibrils cut in cross-section in cytoplasm

Question 34

What is the major contractile unit within the skeletal muscle cell?

Answer 34

myofibrils

Question 35

identify

Answer 35

EM showing high magnification and very high magnification images of cross-section of skeletal muscle showing myofibrils with cross-sectioned thick and thin filaments in hexagonal arrays

Question 36

how are thick and thin filaments seen in EM?

Answer 36

In cross-sections of the myofibril in the EM the thick and thin filaments can be seen to be arranged in hexagonal arrays with each thick filament surrounded by 6 thin filaments.