Lecture 30. Muscle

Question 1

what muscle has multiple peripheral nuclei?

Answer 1

skeletal

Question 2

which muscle is under voluntary control?

Answer 2

skeletal

Question 3

what muscles are under involuntary control?

Answer 3

cardiac and smooth

Question 4

which muscles are striated?

Answer 4

Skeletal and cardiac

Question 5

which muscle contains intercalated discs?

Answer 5

cardiac

Question 6

What muscle cells appear branched with 1-3 central nuclei?

Answer 6

cardiac

Question 7

which muscle cells are uninucleated?

Answer 7

smooth

Question 8

which muscle cells are not striated?

Answer 8

smooth

Question 9

which muscle cells are not striated?

Answer 9

smooth

Question 10

which muscle cells are not striated?

Answer 10

smooth

Question 11

What attaches muscle to bones?

Answer 11

Tendons

Question 12

What is the size of muscle fibre?

Answer 12

long up to 35 cm
0,1 mm

can be seen with a naked eye

Question 13

Structure of the muscle

Answer 13

Muscle-> fascicles-> muscle fibers/cells-> myofibrils->sarcomere-> microfilaments

Question 14

H zone

Answer 14

lighter middle section only thick filaments

Question 15

A band

Answer 15

extends the length of myosin filaments

both thin and thick filaments

Question 16

M line

Answer 16

Line of protein myomesin that connects the thick myosin filaments in the center of sarcomere

Question 17

Z disc

Answer 17

joins thin filaments

marks the ends of sarcomere

Question 18

I band

Answer 18

“Light”

only thin filaments

Question 19

Z disc function

Answer 19

join thin filaments
connect myofibrils to one another
mark the borders of sarcomere

Question 20

what protein is M line made of?

Answer 20

myomesin

Question 21

T-tubules

Answer 21

transverse tubules
- deep invaginations are continuous with the sarcolemma (cell membrane) and circle each sarcomere at each of the junctions of the A and I bands.

cover every myofibril

Question 22

How many t tubules are there per sarcomere?

Answer 22

2

Question 23

Sarcoplasmic reticulum

Answer 23

The calcium storage site around muscle cells. The terminal cisternae of the SR lie close to the T-tubules.

Question 24

t-tubules function

Answer 24

conduct AP to the SR

Question 25

triad

Answer 25

SR-t-tubule-SR structure for each t-tubule there is SR on each side

Question 26

What are the contents of T-tubule?

Answer 26

as it is an extention of cell membrane it has the same contents as extracellular fluid on the inside

Question 27

Thick filaments structure

Answer 27

• Composed of Myosin • Each myosin has 2 subunits each with a globular head and a tail, the two tails intertwine to form a helix. Arranged in a polarised fashion- The heads face out/away from M-line and the tails face in. • The heads have a binding site for actin. The head is an enzyme that hydrolyses ATP( ATPase) Titin anchors the thick filaments to the Z-line

Question 28

titin role

Answer 28

Titin anchors the thick filaments to the Z-line

Question 29

How does the myosin head change shape

Answer 29

ATP hydrolisis

Question 30

what protein is the thin filament primarily comprised of?

Answer 30

Actin

Question 31

What is the shape of the thin filament?

Answer 31

``` The actin filaments are composed of a double stranded helical actin chain (polymers). ```

Question 32

What are the regulatory proteins associated with actin in skeletal and cardiac muscle?

Answer 32

troponin and tropomyosin

Question 33

troponin function

Answer 33

Regulated by Ca2+. When Ca2+ binds to troponin it moves the tropomyosin of myosin binding

Question 34

tropomyosin function

Answer 34

interacts with the myosin binding site on actin and prevents myosin from binding

Question 35

Sliding filament theory of muscle contraction

Answer 35

The sarcomere shortens as the thin filaments are pulled over the thick filaments: • The Z-line is pulled toward the M-line • The I band and H zone become narrower A line now takes up a bigger % of the sarcomere the filaments do not change in length, they just slide over each other

Question 36

4 major steps of the cross-bridge cycle

Answer 36

1. Cross-bridge formation 2. Power stroke 3. Detachment 4. Energization of myosin head

Question 37

1. cross bridge formation

Answer 37

Myosin binds to the actin binding site to form a cross-bridge Note: cross-bridges can only occur in the presence of calcium when the myosin binding site on actin is exposed.

Question 38

2.The power stroke

Answer 38

• ADP is released • The myosin head rotates to its low energy state (about 45° to the actin) pulling with it the thin filament Myosin head still attached • The result is shortening of the sarcomere.

Question 39

3. Detachment

Answer 39

• A new ATP molecule binds to the myosin • The actin-myosin bind is weakened and the myosin detaches • (Note: No ATP = no detachment)

Question 40

4. Energization of the myosin head

Answer 40

• Myosin head hydrolyzes the ATP to ADP + Pi • The myosin head moves back to its “high energy (cocked)” confirmation (about 90° to the actin)

Question 41

Why is calcium important?

Answer 41

- "on" switch for cross-brindge cycle to begin - binds to troponin to move tropomyosin away from the myosin binding site - the cross bridge cycle will continue as long as calcium levels remain above crtical threshold( 0.001-0.01mM) - Need Free calcium. Needs to be released from SR

Question 42

why can heart beat by itself

Answer 42

The heart has its own electrical system that causes it to beat and pump blood. When supplied with nutrients like Ca2+ and Magnesium can beat outsdie the body

Question 43

How is Ca2+ removed?

Answer 43

Active transport pumps (Ca2+ ATPase) are constantly | moving Ca2+ from the cytoplasm back into the sarcoplasmic reticulum

Question 44

Isotonic contraction

Answer 44

Shortening Tension constant Velocity variable (eg bicep curls)

Question 45

Isometric contraction

Answer 45

No shortening Length constant Tension variable (hold)

Question 46

Is cross-bridge cycle still occurring in the isometrically contracted muscle?

Answer 46

Yes. Some minimal movement occurs that is immediately counteracted by the opposing force