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AS/A-Level Biology > I/E: Muscle Contraction > Flashcards

I/E: Muscle Contraction Flashcards

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1
Q

Skeletal muscles

A

Used for movement and attached to bones by tendons.

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2
Q

Ligaments

A

Attach bones to other bones.

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3
Q

What type of muscles are skeletal muscles?

A

Antagonistic - contract and relax to move bones at a joint.

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4
Q

Explain the concept of antagonistic pairs:

A

One muscle contracts and the other relaxes.

Contracting muscle = agonist

Relaxing muscle = antagonist

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5
Q

What are skeletal muscles made up of?

A

Muscle fibres

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6
Q

Sarcolemma

A

Cell membrane of muscle fibres

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7
Q

Transverse (T) tubules

A

Inner folds of the sarcolemma that help to spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre.

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8
Q

Sarcoplasm

A

Cytoplasm of the muscle cell.

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9
Q

Muscle fibres

A

Large bundles of long cells that make up the skeletal muscle.

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10
Q

Sarcoplasmic reticulum

A

A network of internal membranes that run through the sarcoplasm, storing and releasing calcium ions that are needed for muscle contraction.

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11
Q

Myofibrils

A

Long, cylindrical organelles found in skeletal muscles that are made up of proteins and are highly specialised for contraction.

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12
Q

Give 3 characteristics of muscle cells:

A
  • Lots of mitochondria to provide ATP for muscle contraction.
  • Multinucleate - contain many nuclei.
  • Myofibrils - highly specialised for contraction.
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13
Q

Describe the overall structure of a skeletal muscle:

A

Muscle –> muscle fibre –> myofibril

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14
Q

What are myofibrils made up of?

A

Myosin and actin (myofilaments) that move past each other to make muscles contract.

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15
Q

Used for movement and attached to bones by tendons.

A

Skeletal muscles

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16
Q

Attach bones to other bones.

A

Ligaments

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17
Q

Cell membrane of muscle fibres

A

Sarcolemma

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18
Q

Inner folds of the sarcolemma that help to spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre.

A

Transverse (T) tubules

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19
Q

Cytoplasm of the muscle cell.

A

Sarcoplasm

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20
Q

Large bundles of long cells that make up the skeletal muscle.

A

Muscle fibres

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21
Q

A network of internal membranes that run through the sarcoplasm, storing and releasing calcium ions that are needed for muscle contraction.

A

Sarcoplasmic reticulum

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22
Q

Long, cylindrical organelles found in skeletal muscles that are made up of proteins and are highly specialised for contraction.

A

Myofibrils

23
Q

Myosin

A

Protein that makes up thick myofilaments.

24
Q

Actin

A

Protein that makes up thin myofilaments.

25
Q

A-bands

A

Dark bands of the myofibril that contains the thick myosin filaments and some overlapping thin actin filaments.

26
Q

I-bands

A

Light bands of the myofibril that contains thin actin filaments only.

27
Q

Sarcomeres

A

Short units that makes up the myofibril.

28
Q

Z-line

A

Marks the end of each sarcomere.

29
Q

M-line

A

Marks the middle of each sarcomere.

30
Q

H-zone

A

The zone around the M-line that only contains myosin filaments.

31
Q

Protein that makes up thick myofilaments.

A

Myosin

32
Q

Protein that makes up thin myofilaments.

A

Actin

33
Q

Dark bands of the myofibril that contains the thick myosin filaments and some overlapping thin actin filaments.

A

A-bands

34
Q

Light bands of the myofibril that contains thin actin filaments only.

A

I-bands

35
Q

Short units that makes up the myofibril.

A

Sarcomeres

36
Q

Marks the end of each sarcomere.

A

Z-line

37
Q

Marks the middle of each sarcomere.

A

M-line

38
Q

The zone around the M-line that only contains myosin filaments.

A

H-zone

39
Q

Explain the sliding filament theory in relation to muscle contraction:

A
  • Myosin and actin filaments slide over one another to make the sarcomeres contract.
  • Simultaneous contraction of lots of sarcomeres means myofibrils and muscles contract.
  • Sarcomeres return to their original length as the muscle relaxes.
40
Q

According to the sliding filament theory, during muscle contraction what happens to the length of:

  • the A-band?
  • the I-band?
  • the H-zone?
  • the sarcomere as a whole?
A

A-band stays the same length

I-band gets shorter

H-zone gets shorter

Sarcomeres get shorter.

41
Q

Describe the heads of myosin filaments:

A
  • Globular
  • Hinged
  • Binding site for actin
  • Binding site for ATP.
42
Q

Actin-myosin binding sites

A

Binding sites for myosin heads found on actin filaments.

43
Q

Binding sites for myosin heads found on actin filaments.

A

Actin-myosin binding sitesActin

44
Q

Tropomyosin

A

Protein found between actin filaments that helps myofilaments move past each other.

45
Q

Protein found between actin filaments that helps myofilaments move past each other.

A

Tropomyosin

46
Q

11 points/steps

Describe how muscle contraction is triggered by an influc of calcium ions:

A
  1. Stimulation of muscle cell depolarises the sarcolemma and spreads down the T-tubules to the sarcoplasmic reticulum.
  2. SR releases stored Ca2+ ions into the sarcoplasm.
  3. Ca2+ binds to protein attached to tropomyosin, causing it to change shape - pulls attached tropomyosin out of the actin-myosin binding site.
  4. Exposes the binding site, allowing the myosin head to bind.
  5. Actin-myosin cross bridge forms.
  6. Ca2+ activates ATP hydrolase which hydrolyses ATP to provide energy.
  7. Causes myosin head to bend, pullling the actin filament in a rowing action.
  8. Another ATP molecule provides energy to break actin-myosin cross bridge, so myosin head detached from actin filament.
  9. Myosin head reattaches to a different binding site further along the actin filament.
  10. New actin-myosin cross bridge forms and the cycle repeats as long as Ca ions are present.
  11. This shortens the sarcomere.
47
Q

In resting muscles, what blocks the binding sites?

What does this mean?

A

Actin-myosin binding site is blocked by tropomyosin.

Myofilaments can’t slide past each other because the myosin heads can’t bind to the actin-myosin binding site on the actin filaments.

48
Q

In a muscle, what happens when excitation stops/the muscle stops being stimulated?

A
  1. Ca2+ leave binding sites and are moved by active transport back into sarcoplasmic reticulum.
  2. ATP is needed.
  3. Causes the tropomyosin to move back, so they block the actin-myosin binding sites again.
  4. Muscles aren’t contracted as there are no myosin heads attached to actin filaments.
  5. Actin filaments slide back to relaxed position, lengthening the sarcomere.
49
Q

Name the main 3 ways that ATP is continually generated so that exercise can continue:

A
  1. Aerobic respiration
  2. Anaerobic respiration
  3. ATP-Phosphocreatine (PCr) system
50
Q

How is most ATP generated during aerobic respiration?

What exercise is aerobic respiration good for an why?

A
  • Most ATP generated via oxidative phosphorylation in mitochondria.
  • Good for low-intensity exercise as it only works when there’s oxygen.
51
Q

How is ATP generated during anaerobic respiration?

What type of exercise is anaerobic respiration good for and why?

A
  • ATP is rapidly made by glycolysis.
  • Good for short periods of hard exercise, as the end product of glycolysis is pyruvate which is converted to lactate by lactate fermentation.
  • Lactate build up can cause muscle fatigue.
52
Q

How does the PCr system generate ATP?

Where is PCr stored?

What exercise is PCr best for and why?

A
  • ATP is phosphorylated using a phosphate group taken from PCr.
  • Stored inside cells.
  • Best for short bursts of vigorous exercise as it generates ATP very quickly and runs out after a few seconds.
53
Q

What are the two types of muscle fibres in skeletal muscles?

A

Slow twitch and fast twitch

54
Q

What are the differences between slow and fast twitch muscle fibres?

  • Contraction speed?
  • Found in high proportion where?
  • Good for what type of exercise?
  • Tiredness?
  • Releasing energy?
  • Colour?
  • Mitochondria and blood vessels?
A
  • ST contract slowly, FT contract quickly.
  • ST high proportion in muscles used for posture, FT high proportion in muscles used for fast movement.
  • ST good for endurance activities, FT good for short burst of speed and power.
  • ST can work for a long time without getting tired, FT get tired easily.
  • ST release energy slowly through aerobic respiration, FT release energy quickly through anaerobic respiration using glycogen.
  • ST reddish colour as rich in myoglobin, FT whitish in colour as low in myoglobin.
  • ST have lots of mitochondria and blood vessels supplying muscle with oxygen, FT have few mitochondria and blood vessels.

AS/A-Level Biology (190 decks)

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