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HUBS191 - RUBY > lecture 9 - muscle tension/contraction > Flashcards

lecture 9 - muscle tension/contraction Flashcards

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1
Q

What are the key components of the myofilament?

A

Actin and myosin

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2
Q

What is actin in a myofibril?

A

A thin filament that runs along the myofilament and forms a structural scaffold.

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3
Q

What is myosin in the myofibril?

A

Myosin is a thick filament that acts as a motor molecule, when attaching to actin, generating a force.

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4
Q

What are the relative positions of Actin and Myosin and rest?

A

They are not in contact.

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5
Q

What must be supplied to the myofilament for contraction to occur?

A

Calcium ions (Ca2+)

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6
Q

What is a cross-bridge?

A

A bond between actin and myosin that allows the sarcomere to contract and shorten towards its centre.

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7
Q

What are the 5 states of the cross bridge cycle?

A

Attached, Released, Cocked, Cross-bridge, Power-stroke.

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8
Q

What is the attached state of the cross-bridge cycle?

A

Myofilament has just finished a power stroke (ADP and P has been released from myosin head), and the actin-myosin cross bridges are still present.

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9
Q

What is the released state of the cross-bridge cycle?

A

A molecule of ATP binds to myosin, causing its head to detach from actin, removing the cross-bridge.

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10
Q

What is the cocked state of the cross-bridge cycle?

A

The Myosin head burns ATP to make energy and a phosphate group binds to it. Energy is stored by changing the shape of Myosin, preparing it to attach to actin again.

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11
Q

What is the cross-bridge state of the cross-bridge cycle?

A

If calcium is present, the myosin head binds to the actin myofilament forming a cross bridge.

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12
Q

What is the power-stroke state?

A

The energised myosin head uses its stored energy to change conformation, releasing P and creating a power stroke that causes filaments to slide past each other to contract the sarcomere.

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13
Q

What are the two factors that muscle tension is dependent on?

A

The number of muscle fibres recruited and the rate at which the muscle is stimulated.

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14
Q

If a small number of neurons are active, muscle force will be…?

A

Low

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15
Q

What is the name of the process of activating more muscle fibres to generate more force?

A

Recruitment

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16
Q

What will a single action potential generate in muscle fibres?

A

A pulse of Ca2+ will be released into the cytoplasm causing a brief period of tension - a twitch

17
Q

What is a twitch in terms of muscle contraction?

A

When a muscle if briefly stimulated when it is relaxed, causing a small amount of tension to be produced.

18
Q

What happens when many action potentials are fired to a muscle fibre in rapid sequence?

A

The muscle will be restimulated before Ca2+ has returned to the SR, meaning it will increase further, creating a longer actin-myosin interaction and a stronger, longer contraction.

19
Q

What is the state when maximum signalling and contraction of a muscle fibre is reached?

A

Tetanus

20
Q

What is the length-tension relationship?

A

Each muscle has an optimal length where it is strongest, where there is sufficient length for cross bridging AND contraction.

21
Q

Why are stretched muscles unable to contract effectively?

A

There is not enough overlap of the myosin and actin fibres, so cross-bridging is limited/does not occur.

22
Q

Why are muscles that are bent not effective at lifting weight?

A

The myosin and actin fibres overlap completely - there is no room for contraction to occur.

23
Q

Why do fast muscle fibres get fatigued rapidly?

A

They provide a lot of energy quickly, generating a short, powerful force.

24
Q

Which muscle fibre (slow/fast) has a larger fibre diameter?

A

Fast

25
Q

Which muscle fibre (slow/fast) has a greater capillary supply?

A

Slow (they need to produce a lot of energy when in use)

26
Q

Which muscle fibre (slow/fast) has more mitochondria?

A

Slow

27
Q

Why do fast fibres not have mitochondria?

A

Mitochondria provides energy too slowly, making it ineffective in providing the rapidly released high levels of energy required.

28
Q

What colour are fast muscle fibres?

A

White

29
Q

What colour are slow muscle fibres?

A

Red

30
Q

Which muscle fibre (slow/fast) has better fatigue resistance?

A

Slow

31
Q

Which muscle fibre (slow/fast) reaches peak tension more rapidly?

A

Fast

32
Q

How can muscle contraction be described in terms of the ‘lines’ of the sarcomere?

A

Myosin contracts, pulling the Z lines of the actin inwards the M line of the myosin, shortening the sarcomere on both sides of the M line.

33
Q

Is the M line found in the myosin or actin filaments?

A

Myosin (in the centre of the sarcomere)

34
Q

is the Z line found on actin or myosin filaments?

A

Actin

HUBS191 - RUBY (36 decks)

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