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biosci block 6 & 7 > Lecture 30. Muscle > Flashcards

Lecture 30. Muscle Flashcards

1
Q

what muscle has multiple peripheral nuclei?

A

skeletal

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2
Q

which muscle is under voluntary control?

A

skeletal

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3
Q

what muscles are under involuntary control?

A

cardiac and smooth

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4
Q

which muscles are striated?

A

Skeletal and cardiac

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5
Q

which muscle contains intercalated discs?

A

cardiac

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6
Q

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

A

cardiac

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7
Q

which muscle cells are uninucleated?

A

smooth

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8
Q

which muscle cells are not striated?

A

smooth

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9
Q

which muscle cells are not striated?

A

smooth

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10
Q

which muscle cells are not striated?

A

smooth

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11
Q

What attaches muscle to bones?

A

Tendons

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12
Q

What is the size of muscle fibre?

A

long up to 35 cm
0,1 mm

can be seen with a naked eye

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13
Q

Structure of the muscle

A

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

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14
Q

H zone

A

lighter middle section only thick filaments

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15
Q

A band

A

extends the length of myosin filaments

both thin and thick filaments

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16
Q

M line

A

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

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17
Q

Z disc

A

joins thin filaments

marks the ends of sarcomere

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18
Q

I band

A

“Light”

only thin filaments

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19
Q

Z disc function

A

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

20
Q

what protein is M line made of?

A

myomesin

21
Q

T-tubules

A

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

22
Q

How many t tubules are there per sarcomere?

A

2

23
Q

Sarcoplasmic reticulum

A

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

24
Q

t-tubules function

A

conduct AP to the SR

25
Q

triad

A

SR-t-tubule-SR structure

for each t-tubule there is SR on each side

26
Q

What are the contents of T-tubule?

A

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

27
Q

Thick filaments structure

A

• 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

28
Q

titin role

A

Titin anchors the thick filaments to the Z-line

29
Q

How does the myosin head change shape

A

ATP hydrolisis

30
Q

what protein is the thin filament primarily comprised of?

A

Actin

31
Q

What is the shape of the thin filament?

A 
The actin filaments are composed of a double stranded helical
actin chain (polymers).
32
Q

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

A

troponin and tropomyosin

33
Q

troponin function

A

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

34
Q

tropomyosin function

A

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

35
Q

Sliding filament theory of muscle contraction

A

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

36
Q

4 major steps of the cross-bridge cycle

A
  1. Cross-bridge formation
  2. Power stroke
  3. Detachment
  4. Energization of myosin head
37
Q
  1. cross bridge formation
A

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.

38
Q

2.The power stroke

A

• 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.

39
Q
  1. Detachment
A

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

40
Q
  1. Energization of the myosin head
A

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

41
Q

Why is calcium important?

A
  • “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
42
Q

why can heart beat by itself

A

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

43
Q

How is Ca2+ removed?

A

Active transport pumps (Ca2+ ATPase) are constantly

moving Ca2+ from the cytoplasm back into the sarcoplasmic reticulum

44
Q

Isotonic contraction

A

Shortening
Tension constant
Velocity variable

(eg bicep curls)

45
Q

Isometric contraction

A

No shortening
Length constant
Tension variable

(hold)

46
Q

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

A

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

biosci block 6 & 7 (8 decks)

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