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BIOLOGY > Topic 6 - Skeletal Muscles > Flashcards

Topic 6 - Skeletal Muscles Flashcards

1
Q

What are myofibrils made up of?

A

They are made up of fused cells that share nuclei and cytoplasm (sarcoplasm)

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2
Q

Why do myofibrils appear striped?

A

They have alternating light and dark coloured bands:
- Light = I (isotropic) -> no overlap
- Dark = A (anisotropic) -> overlap of thin and thick filaments.

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3
Q

What are the light bands in a myofibril?

A

Isotropic bands

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4
Q

What are the dark bands in a myofibrils?

A

Anisotropic bands

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5
Q

What is a sarcomere formed from?

A

Myofibrils

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6
Q

What happens to a sarcomere in muscle contraction?

A

The sarcomeres shorten and the pattern of light and dark bands changes.

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7
Q

What are thick filaments made up of?

A

Myosin molecules

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8
Q

What are thin filaments made up of?

A

Actin molecules

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9
Q

Explain the characteristics of the thick filaments

A

fibrous protein molecules
globular head
fibrous part anchors the molecule into the thick filament
myosin head points away from the M line.

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10
Q

Explain the characteristics of the thin filaments

A

globular protein molecules
many link together to form a chain
two actin chains twist together to form one thin filament.
tropomyosin is twisted around the two actin chains.

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11
Q

What is the I band?

A

Isotropic bands that appear lighter as there is no overlap (contains only actin)

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12
Q

What is the A band?

A

Anisotropic band that are the overlap of thin and thick filaments and span the total width of the myosin.

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13
Q

What is the M line?

A

Holds the myosin fibres and forms part of the sarcomere in the middle.

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14
Q

What is the Z line?

A

Joins the actin together and makes one repeating unit of myofibrils.

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15
Q

What is the H zone?

A

At the centre of the A band and contains myosin only.

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16
Q

What happens when the calcium ions enter in muscle contraction?

A

They cause the tropomyosin that block the binding sites to move.

17
Q

Where do the myosin heads attach to in the first step of muscle contraction?

A

They bind to the exposed binding site on the actin molecule, forming a cross bridge.

18
Q

How does the myosin head move along the thin filament ?

A

In a ‘rowing action’

19
Q

Where is the thin filament pulled to in muscle contraction?

A

To the centre of the sarcomere

20
Q

What happens when the ATP binds to the myosin head in muscle contraction?

A

It causes the myosin head to separate from the actin filament.

21
Q

How is ADP released in muscle contraction?

A

When the angle is created in the cross bridge, it creates tension and as a result the actin filament is pulled and slides along the myosin.in doing so, the ADP molecule is released (with the use of ATPase)

22
Q

What needs to happen to ensure that the cycle is repeated in muscle contraction?

A

The concentration of calcium ions must remain high.

23
Q

How does phosphocreatine aid muscle contraction?

A

It provides phosphate to regenerate ATP from ADP.

24
Q

What is the structure of slow twitch muscle fibres?

A

They contain a large store of myoglobin, a rich supply of blood and many mitochondria.

25
Q

Where are slow twitch muscle fibres found?

A

Calf muscles

26
Q

What are the properties of slow twitch muscle fibres?

A

Contract slower
Respire aerobically for longer periods of time
Adapted for endurance work

27
Q

What is the structure of fast twitch muscle fibres?

A

They are thicker due to more myosin filaments, have a large store of glycogen and a store of phosphocreatine to help make ATP and a high concentration of enzymes involved in aerobic respiration.

28
Q

Where are fast twitch muscle fibres found?

A

Biceps

29
Q

What are the properties of fast twitch muscle fibres?

A

Contract faster to provide short burst of powerful contraction
Adapted for intense exercise such as sprinting and weight lifting.

30
Q

Describe the process of muscle contraction

A
  1. An action potential from a motor neuron depolarises the sarcolemma and spreads down the T tubules.
  2. This causes the sarcoplasmic reticulum to release stored calcium ions into the sarcoplasm.
    Calcium ions bind to a protein attached to tropomyosin causing the actin-myosin binding sites to change shape, pulling the tropomyosin out.
  3. The now exposed binding site allows the myosin head to bind to the actin forming a cross bridge.
  4. Calcium ions also activates ATP hydrolysis
  5. The energy released from ATP causes the myosin head to bend, moving the actin filament along.
  6. Another ATP molecule provides energy to break the actin myosin cross-bridge so that the myosin head is detached.
  7. The myosin head reattaches to another binding site and the cycle is repeated for as long as the concentration of calcium ions is high enough.
  8. The muscles stop contracting when calcium ions move back into the sarcoplasmic reticulum via active transport.

BIOLOGY (41 decks)

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