Muscle I

Question 1

What do you call the cytoplasm, smooth ER, and cell membrane in muscle cells?

Answer 1

Sarcoplasm, sarcoplasmic reticulum, sarcolemma

Question 2

What are the two types of striated muscle?

Answer 2

Skeletal and cardiac

Question 3

What is the non-striated muscle type?

Answer 3

Smooth muscle

Question 4

Describe the general structure/contraction of skeletal muscle. Where is it usually found?

Answer 4

Long, multi-nucleated cells intended for quick, forceful contractions under voluntary control.

Axial, extremity, and cranial bones

Question 5

Describe structure/contraction of cardiac muscle.

Answer 5

Elongated, branched cells connected to each other through intercalated discs. Rhythmic, forceful contractions that are involuntary.

Question 6

Describe the general structure/contraction of smooth muscle. Where is it commonly found?

Answer 6

Simple, slow involuntary contractions.

Present in vessels, airways, GI, and GU tracts.

Question 7

Where do muscle cells originate from? What is general structure of a muscle cell?

Answer 7

Originate from mesoderm.
Myoblasts fuse to form myotubes which differentiate into muscle fibers. Satellite cells sit on top of these muscle fibers and act as progenitor cells if muscle is damaged.

Question 8

What other functions does muscle have besides contractions?

Answer 8

Protein storage and metabolic functions w/ other organs, esp liver

Question 9

Which muscle type is predominant in our bodies?

Answer 9

Skeletal

Question 10

Describe organization of skeletal muscle in terms of connective tissue.

Answer 10

1. Endomysium - conn. tissue that bundles myofibers into fasicles
2. Perimysium - conn. tissue that bundles fasicles
3. Epimysium - dense conn. tissue that surrounds entire muscle

Question 11

Describe cellular organization of striated muscle. What makes it striated?

Answer 11

Longitudinally arranged myofibers that contain contractile units called sarcomeres.

Striations due to alternating I-bands and A-bands.

Question 12

What are the thick and thin filaments that make up the sarcomere.

Answer 12

Thick - myosin, thin - actin

Question 13

What is actin anchored in?

Answer 13

Z-lin

Question 14

What is myosin anchored in?

Answer 14

M-line

Question 15

Where do myosin and actin overlap? (Dark region)

Answer 15

A-band

Question 16

Where do myosin and actin NOT overlap? (Light region)

Answer 16

I-band

Question 17

What is the H-zone?

Answer 17

Where myosin is attached to M-line, but does not overlap with actin (lighter zone of A-band)

Question 18

What are the two regulatory proteins that act on actin?

Answer 18

Troponin and tropomyosin

Question 19

What does titin do? Where is it located?

Answer 19

Connects myosin to Z-disc, present in the I-band

Question 20

What does nebulin do?

Answer 20

It’s a spacer/linker protein between actin.

Question 21

What is the source of emergency high energy phosphate in the muscle cell? Where is it located?

Answer 21

Creatine kinase - the H-zone

Question 22

Describe the mechanism of muscle contraction.

Answer 22

1. Bound ATP is hydrolyzed to ADP and Pi on the myosin head.
2. Myosin extends and attaches to binding site on actin, forming a cross-bridge.
3. Power stroke triggers, myosin pulls actin filament towards M line.
4. Sarcomere shortens as Z line draws closer to M line and muscle contracts.
5. ADP and Pi are released
6. ATP binds to myosin, freeing myosin from actin

Question 23

Describe mechanism of muscle contraction regulation.

Answer 23

1. Tropomyosin blocks cross-bridge binding sites on actin in relaxed muscle state.
2. When neurotransmitters bind to receptors on cell membrane, depolarizes muscle fiber membrane.
3. Electrical impulse travels down T tubules and opens Ca2+ stores in SR.
4. Ca2+ flows into myofibrils.
5. When Ca2+ levels are high enough and there is ATP, Ca2+ binds troponin.
6. Troponin displaces tropomyosin, exposing myosin binding sites on actin.
7. Myosin can now bind actin and form cross bridge.