L9 - Muscle Contraction Flashcards Preview

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Flashcards in L9 - Muscle Contraction Deck (23)
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1
Q

What is a muscle fibre?

A

Cells that convert ATP into mechanical energy, specialised in force and movement

2
Q

What are myofibrils?

A

fibres made up of contractile proteins actin and myosin, and some control proteins

3
Q

What is the basic functional and structural unit of a muscle fibre called?

A

Sarcomere

4
Q

Where does ATP bind to in order to provide energy for muscle contraction?

A

Myosin head

5
Q

Why would you ‘skin’ cold glycerol or Triton-X?

A

This removes cells and other lipid membranes, allowing an experimenter to bath actin and myosin filaments in other fluids.

Concentrated salt solution (with no Ca2+) causes actin and myosin to separate from each other

6
Q

What do myosin molecules do when bathed in dilute salt?

A

They assemble into bi-polar filaments (1.6 um long)

7
Q

How many subunits does Troponin have, and what does each bind?

A

3

1 binds actin, 1 binds tropomyosin, and 1 binds Ca2+

8
Q

Does the thickness of filaments change when the muscle contracts?

A

No - but the extent at which they overlap each other does

9
Q

What was a critical test of the sliding filament theory?

A

To demonstrate that the force produced by a muscle fibre when it is activated is proportional to the overlap between thick & thin filaments, therefore to the number of cross bridges that could form between the actin and myosin heads.

10
Q

Who proposed the ‘sliding filament’ theory?

A

Huxley and Huxley independently proposed a sliding filament theory of muscle contraction

11
Q

What methods did Huxley and Huxley individually use to find out about muscle contraction?

A

Electron and Interference microscopy

12
Q

What is the cross-bridge cycle?

A

1) Myosin head binds to actin forming a crossbridge & its orientation changes, exerting a force that causes actin to slide along myosin.
2) Myosin head then binds to ATP & releases actin. It then returns to its original formation ready for next cycle.
3) ATP is needed to break the actin–myosin bonds, which accounts for rigor mortis. .

13
Q

What protein hold myosin in the sarcomere?

A

Titin

14
Q

What roles does Calcium play in muscle contraction?

A

Ca2+ binds to troponin, this causes the troponin molecule to move, pulling tropomyosin out of the way, allowing the myosin heads to bind to actin.

15
Q

What makes myosin heads release from actin after contraction

A

the binding again to ATP

16
Q

What controls tension, and therefore the amount of force of a muscle fibre?

A

The muscle fibre membrane potential

17
Q

How does electrical excitation cause Ca2+ release?

A

1) An AP arrives at the axon terminal causing vesicles of ACh to be released.
2) The postsynaptic membrane generates an AP that spreads down the T-tubule
3) Depolarisation of T-tubules causes the release of Ca2+ from the SER into the cytoplasm.
4) Released Ca2+ diffuses in the sarcoplasm, stimulating muscle contraction

18
Q

Where are T-tubules associated with sarcoplasmic reticulum’s?

A

At triads

19
Q

How long does the cross bridge cycle continue and how does it stop?

A

The cycle repeats as long as Ca2+ is high.

When electrical excitation stops, the SER mops up Ca2+

20
Q

What is the evidence that electrical excitation of a muscle cell outer membrane controls development of force?

A

p

21
Q

What is the evidence that electrical excitation of a muscle cell outer membrane controls development of force?

A

p

22
Q

Does the length of a muscle fibre affect its strength?

A

No. It is the degree of overlap between actin and myosin filaments in individual sarcomeres that matters. Force in one sarcomere does not add to force within the next in a muscle fibre – they are independent functional units. Because sarcomere length does not vary much between different muscles in vertebrates, their individual muscle fibres also do not vary much in strength. The only way to make a muscle stronger is to make it more wide, increasing the number of filaments pulling in parallel by either adding more muscle fibres or making individual fibres wider. A long muscle fibre will be able to contract further than a short muscle fibre because the distance of shortening by individual sarcomeres does add up.

23
Q

What would be the difference in speed of contraction between a fibre with short compared with long sarcomeres?

A

the fibre with short sarcomeres will contract the fastest. When the muscle is activated to shorten, the individual sarcomeres will each shorten by (roughly) the same amount: more sarcomeres means a greater length of shortening in a given time. (The muscle with longer sarcomeres will be able to generate the greater force – a long sarcomere has more cross-bridges)