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BIOS4001 - Skeletomuscular System > Mechanism of Muscle Contraction > Flashcards

Mechanism of Muscle Contraction Flashcards

1
Q

Explain the 1st step of excitation-contraction coupling

A
  • acetylcholine (ACh) released from axon terminal of motor neuron & binds to receptors of a motor end plate.
  • binding elicits an end-plate potential, triggering an action potential in the muscle cell
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2
Q

Explain the 2nd step of excitation-contraction coupling

A

Action potential propagates along sarcolemma & down T tubules

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3
Q

Explain the 3rd step of excitation-contraction coupling

A

Action potential triggers Ca2+ release from sarcoplasmic reticulum

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4
Q

Explain the 4th step of excitation-contraction coupling

A

Ca2+ binds to troponin
- exposing myosin-binding sites

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5
Q

Explain the 5th step of excitation-contraction coupling

A

Cross-bridge cycle begins (muscle fiber contracts)

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6
Q

Explain the 6th step of excitation-contraction coupling

A
  • Ca2+ is actively transported back into lumen of sarcoplasmic reticulum
  • following the action potential
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7
Q

Explain the 7th step of excitation-contraction coupling

A

Tropomyosin blocks myosin-binding sites (muscle fiber relaxes)

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8
Q

What does the sliding filament theory involve?

A
  • myosin
  • actin
  • tropomyosin
  • troponin
  • ATP
  • calcium ions
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9
Q

What is the 1st step of the Contraction Cycle and Cross-Bridge Formation?

A

Arrival of Ca2+ within zone of overlap in sarcomere

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10
Q

What is the 2nd step of the Contraction Cycle and Cross-Bridge Formation?

A
  • Ca2+ binds to troponin
  • weakening bond between actin and troponin-tropomyosin complex
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11
Q

What happens to the troponin molecule in step 2 of the Contraction Cycle?

A

Changes position:
- rolls tropomyosin molecule away from active sites on actin
- allows interaction with the energised myosin heads

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12
Q

What is the 3rd step of the Contraction Cycle and Cross-Bridge Formation?

A
  • active sites exposed
  • energised myosin heads bind to them
  • forming cross-bridges
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13
Q

What is the 4th step of the Contraction Cycle and Cross-Bridge Formation?

A

The power stroke action occurs after formation of bridge:
- energy stored in resting state is released
- as the myosin head pivots toward the M line
- bound ADP & phosphate group are released

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14
Q

What is the 5th step of the Contraction Cycle and Cross-Bridge Formation?

A

When ATP binds to myosin head:
- link between myosin head and active site (on actin molecule) is broken
- active site = exposed
- able to form another cross-bridge

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15
Q

What is the 6th step of the Contraction Cycle and Cross-Bridge Formation?

A

Myosin reactivation occurs when:
- free myosin head splits ATP into ADP and phosphate
- energy released used to recock myosin head

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16
Q

Summarise the Single Cross-Bridge Cycle in 6 steps

A
  1. Exposure of binding sites on actin
  2. Binding of myosin to actin
  3. Power stroke of cross-bridge
  4. disconnecting the myosin head from actin
  5. Re-energising & repositioning myosin head
  6. Removal of Ca ions
17
Q

What happens to the length of the sarcomere during the contraction of a skeletal muscle fibre?

A

Contracts/shortens:
- A band = stays same width
- Z lines = move closer together
- I bands = get smaller
- H zone = changes
- myofilament = no change

18
Q

Because the sarcomere units shorten …

A

the length of the muscle fiber shortens (contracts)

19
Q

When one end of a myofibril is fixed in position …

A

the free end is pulled toward the fixed end

20
Q

What is the role of ATP in the contraction of the skeletal muscle?

A
  • energising the power stroke of the myosin cross-bridges
  • disconnecting myosin head from binding site on actin at the end of a power stroke
  • actively transports Ca ions into sarcoplasmic reticulum
21
Q

What is the role of ATP in the contraction of the skeletal muscle?

A
  • energising the power stroke of the myosin cross-bridges
  • disconnecting myosin head from binding site on actin at the end of a power stroke
  • actively transports Ca ions into sarcoplasmic reticulum
22
Q

What is the 1st step of muscle relaxation?

A

ACh removed from receptors by AChE

23
Q

What is the 2nd step of muscle relaxation?

A

ligand-gated Na+ channels close

24
Q

What is the 3rd step of muscle relaxation?

A

Na/K pumps reestablish the RMP

25
Q

What is the 4th step of muscle relaxation?

A

Ca2+ leave troponin & absorbed back into cisternae

26
Q

What is the 5th step of muscle relaxation?

A

tropomyosin moves back over the actin active site

27
Q

What is the 6th step of muscle relaxation?

A

myosin heads release their binding to actin

28
Q

What 3 forces are needed for muscle relaxation?

A
  • elastic forces
  • opposing muscle contractions
  • gravity

BIOS4001 - Skeletomuscular System (13 decks)

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