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BIOSCI 107 Part Two > Muscles: Skeletal muscle part 1 > Flashcards

Muscles: Skeletal muscle part 1 Flashcards

1
Q

Is skeletal muscle voluntary?

A

Yes

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2
Q

What is the function of skeletal muscle

A

the physical movement of the body

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3
Q

Features of skeletal muscle

A

It has multiple peripheral nuclei
It has single long cylindrical cells
Striated

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4
Q

What attaches skeletal muscle to bones

A

tendons

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5
Q

Length of skeletal muscle fibres

A

35cm

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6
Q

Width of skeletal muscle fibres

A

0.1mm

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7
Q

What are skeletal muscle fibres composed of that contract

A

Myofibrils (contractile filaments)

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8
Q

What are the sections of myofibrils

A

Sacromeres

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9
Q

Thick filaments

A

run the entire length of A band

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10
Q

Thin filaments

A

run the entire length of the I band (only thin) and partway into the A band

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11
Q

Z disc/line

A

coin-shaped sheet of proteins that anchors the thin filaments and connects myofibrils to one another

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12
Q

H Zone

A

lighter mid-region where filaments do not overlap (no thin filaments) ONLY thick

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13
Q

M line

A

line of protein myomesin that holds adjacent thick filaments together

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14
Q

Sacromeres

A

extend from the z line to the next z line. It can contract. Z disc comes closer to the M line. If the Z disc gets closer together,the H zone and I band will get smaller. A band stays the same length

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15
Q

Structural features of T-tubules

A

deep invaginations continuous with the sarcolemma and circle each sarcomere at each of the junctions of the A and I bands.
Folding in of the sarcolemma, goes around twice per sarcomere (at ends of A band)

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16
Q

Function of T-tubules

A

Allows action potentials to be carried deep within the muscle cell and allows extracellular fluid can be close to myofibrils

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17
Q

What is the function of the Sarcoplasmic reticulum (SR)

A

It is a Ca storage site (Ca is on/off switch), takes up Ca so low [Ca] inside cell

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18
Q

What is the terminal cisternae

A

The sacroplasmic reticiulm adjacent to the t-tubules. The terminal cisternae of the SR lie close to the T Tubules, means if AP comes down T tubule it can quickly tell SR to do something

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19
Q

What is a triad

A

2 Terminal cisternae around T tubule

20
Q

What is thick filaments made of

A

myosin

21
Q

How many subunits does each myosin have?

A

2

22
Q

What are the features of the subunits in myosin

A

globular head and a tail - this intertwinses with the tail of the other subunit to form a helix

23
Q

Function of the myosin head

A

to act as a binding site for actin. It also is an enzyme that hydrolyses ATP (an ATPase) because it moves (with hinge)

24
Q

What is the resting state of the myosin head

A

Is being pulled in

25
Q

Arrangement of thick filaments

A

The myosin heads project away from the M-line while the tails of the two subunits are intertwined.

26
Q

Function of titin in thick filaments

A

Titin anchors the thick filament to the Z-line

27
Q

What are thin filaments mainly composed of?

A

Globular actin proteins

28
Q

Strucutural shape of thin filaments

A

double stranded helical actin chain

29
Q

The two regulatory proteins associated with actin in skeletal and cardiac muscle

A

Troponin and tropomyosin

30
Q

Function of tropomyosin

A

It interacts with the myosin binding sites. Initially on top of myosin binding sites (like a plug)

31
Q

Function of troponin

A

It is regulated by Ca2+ and pulls of tropomyosin off binding site

32
Q

Sliding filament theory of muscle contraction

A

Sarcomere shortens as THIN filaments are pulled OVER the thick filaments

  • Z-line is pulled toward the M-line
  • I band and H zone become narrower
  • Myosin stays still
  • Thin actin filaments are pulled OVER myosin
33
Q

What is the starting point of the cross bridge cycle?

A

There is no fixed starting point as it is a cycle

34
Q

What occurs in the “Cross bridge formation” stage of the cross bridge cycle

A

The myosin binding sites are available due to Ca so myosin binds to the myosin binding sites on actin forming a cross-bridge. Myosin has already hydrolyzed ATP (to ADP) (ENERGISED state), it “stretched out” - wants to relax to resting state = holding lots of energy

35
Q

What MUST be present for the cross bridge cycle to occur and why

A

free Calcium in the intercellular space!! so that the myosin binding site on actin is exposed

36
Q

What occurs in the “Power stroke” stage of the cross bridge cycle

A

ADP is released (causing myosin head to pull in: resting state). Myosin head rotates to its low energy state (45° to the actin) pulling with it the thin filament. This causes the sarcomere to shorten

37
Q

What occurs in the “Detachment” stage of the cross bridge cycle

A

A new ATP molecule binds to the myosin. The actin-myosin bond is weakened and the myosin detaches (head lets go of actin)

38
Q

What occurs without the presence of ATP in the cross bridge cycle

A

The myosin head cannot detatch from the myosin binding site in actin > Rigor mortis

39
Q

What occurs in the “Energization of the myosin head” stage of the cross bridge cycle

A

Myosin head hydrolyzes the ATP to ADP + Pi

The myosin head moves back to its “high energy (cocked)” confirmation ( 90° to actin)

40
Q

What is the role of calcium in the cross bridge cycle?

A

Ca ions provide the “on” switch for the cross-bridge cycle to begin. When Ca binds with troponin, the tropomyosin moves to expose the myosin binding sites on actin

41
Q

What is the Ca threshold for the cross bridge cycle

A

0.001-0.01 mM

42
Q

What will a high concenration of Ca in the intercellular space cause in skeletal muscle?

A

A contraction

43
Q

What are the two features of skeletal muscle that regulate calcium?

A

Ca channels and active transport pumps Ca2+ ATPase

44
Q

Where are Ca channels located and how do they function?

A

Ca channels in the sacroplasmic reticulum allow the movement of Ca ions into the cytosol, regulating Ca levels

  • when they are open = Ca release so contraction
  • when they are closed = Ca cannot be released so not enough Ca for a contraction
45
Q

Where are Active transport pumps (Ca2+ ATPase) located and how do they function?

A

They are in the sacroplasmic reticulum and are constantly moving Ca2+ from the cytoplasm back into the sarcoplasmic reticulum. As soon as Ca levels drop - contraction stops

BIOSCI 107 Part Two (17 decks)

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