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biosci > Skeletal Muscle > Flashcards

Skeletal Muscle Flashcards

1
Q

Characteristics of the skeletal muscle

A
  • voluntary control
  • striated
  • single long cylindrical cells
  • multiple peripheral nuclei
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2
Q

What is the structure of muscle cells

A
  • attatched to bones via tendons
  • the cells “muscle fibres” are long and reasonably wide
  • cells composed of myofibrils containing highly organised contractile filaments.
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3
Q

Thick filaments

A

Run the entire length of the A band

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4
Q

Thin filaments

A

Run the length of the I band and partway into the A band

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5
Q

Z disc

A

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

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6
Q

H zone

A

Lighter mid-region where filaments do not overlap

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7
Q

M line

A

Line of protein myomesin that holds adjacent thick filaments together

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8
Q

What are T-tubules

A

Deep invaginations continuous with the sarcolemma (cell membrane) and circle each sarcomereat each of the junctions of the A and I bands.
Allows action potentials to be carried deep within the cell.

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9
Q

What is the sarcoplasma reticulum

A

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

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10
Q

What are thick filaments composed of

A

Myosin, where each myosin has two subunits each with a globular head and a tail, the two tails intertwine to form a helix. The heads have a binding site for actin.

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11
Q

What is myosin

A

A high molecular weight protein that is formed from two high molecular weight sub-units. These subunits have a ‘tail’ which wind around each other in a double helix and globular head that is capable of hydrolysing ATP/

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12
Q

What is the head of the myosin in the thick filament

A
  • An enzyme that hydrolyses ATP (an ATPase).
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13
Q

How is the head in the myosin of the thick filament arranged

A

Arranged in a polarised fashion i.e with the myosin heads projection. Head outside, tail in the middle.

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14
Q

What are thin filaments composed of

A
  • composed primarily of globular actin proteins.
  • filaments composed of a double stranded helical actin chain (polymers)
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15
Q

What are troponin and tropomyosin

A

Regulatory proteins associated with actin in skeletal and cardiac muscle

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16
Q

What is troponin

A

Binding site to Ca2+ which changes shape and forces the tropomyosin off the actin.

17
Q

What does tropomyosin do

A

Interacts with the myosin binding sites

18
Q

What does contraction refer to

A

The activation of myosin’s cross bridges. As the sarcomere contracts, the thin filaments are pulled over the thick filaments. The Z discs are pulled towards the M line and the I band and H zone narrower.

19
Q

At what calcium level is muscle typically relaxed and activated in?

A

Typically relaxed when the calcium level is less than 0.0001 mM and activated at 0.0001mM.

20
Q

What is the sliding door theory of muscle contraction

A

The sarcomere shortens as the thin filaments are pulled over the thick filaments
* the Z line is pulled towards the M line
* the I band and H zone become narrower (thin filaments slide over thick filaments)

21
Q

What are the four major steps in the cross bridge cycle

A
  1. cross-bridge formation
  2. power stroke
  3. detachment
  4. energization of myosin head
22
Q

Cross bridge formation (1)

A

When the myosin binds to the actin binding site, forming a cross-bridge

23
Q

What happens in the power stroke step (2)

A
  • ADP is released
  • the myosin head rotates to its low energy state (about 45 degrees to actin) pulling with it the thin filament
  • the result is shortening of the sarcomere
24
Q

What happens in the detatchment step (3)

A
  • A new ATP molecule binds to the myosin
  • the actin-myosin bind is weakened and the myosin detaches
25
Q

What happens in the energization of the myosin head step (4)

A
  • myosin head hydrolyzes the ATP to ADP + Pi
  • the myosin head moves back to its “high energy (cocked) confirmation - about 90 degrees to the actin.
26
Q

What is the importance of calcium

A

Calcium ions provide the “on-switch” for cross-bridge cycle to begin.

27
Q

Describe the steps into why calcium is needed in the muscles

A

When the calcium binds with troponin the tropomyosin moves to expose the myosin binding sites on actin

The cross-bridge cycle will continue as long as calcium levels remain above the critical threshold (0.001-0.01mM)

28
Q

Calcium regulation: What does the opening of the calcium channels in the SR allow

A

Allows the movement of calcium ions into the cytosol

29
Q

Calcium regulation: Active transport pumps

A

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

30
Q

Isotonic

A
  • shortening
  • tension constant
  • velocity variable

biosci (28 decks)

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