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Physiology and Disease > Molecular basis of muscle contraction > Flashcards

Molecular basis of muscle contraction Flashcards

1
Q

what connects skeletal muscle to bone?

A

tendon

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2
Q

structure of skeletal muscle (3)

A
  1. muscle fibre (cell) wrapped in endomysium
  2. cells bundled and surrounded by perimysium to form fascicle
  3. fascicles bundled within epimysium
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3
Q

myofibril (2)

A
  1. small fibres within muscle cells
  2. striated
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4
Q

sliding filament model of muscle contraction (2)

A

Thin (actin)/thick (myosin) filaments
1. thick filaments pull thin filaments from both ends towards middle when activated by ATP
2. more overlap between thin filaments mean more muscle contraction

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5
Q

Thin filaments

A

actin

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6
Q

thick filaments

A

myosin

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7
Q

cross-brige cycle (5)

A
  1. ATP hydrolyses, energises myosin head to form cross-bridge with actin
  2. Pi dissociates making bond between actin and myosin stronger
  3. ADP released and myosin head pivots
  4. when new ATP binds to myosin link between actin/myosin weakens
  5. ATP hydrolysed to ADP and Pi and so on…
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8
Q

what does the cross-bridge cycle allow for?

A

muscle contraction

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9
Q

why do thin/thick filaments overlap?

A

result of cross-bridge formation between myosin head and actin

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10
Q

sarcomere

A

basic functional unit of striated muscle tissue

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11
Q

Z-discs (2)

A
  1. black thin lines surrounded by whiteish area
  2. 2 adjacent Z discs define a sarcomere
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12
Q

I band (2)

A
  1. whitish area
  2. defines width of filament, shortens when muscle contracts
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13
Q

A band (2)

A
  1. thick filament (entire length of myosin)
  2. doesn’t change width
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14
Q

describe how muscle cells relax (3)

A
  1. interaction between actin and myosin prevented when muscle is relaxed
  2. myosin binding sites on actin filament prevented by thin filament (tropomyosin)
  3. at rest tropomyosin intertwines with actin filament
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15
Q

Troponin

A

Troponin is a complex of three proteins that attaches to and regulates tropomyosin

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16
Q

how many myosin binding sites does each actin molecule have?

A

1

17
Q

role of tropomyosin

A

covers myosin-binding site of actin molecules, prevents actin-myosin interaction

18
Q

how many calcium ion binding sites does each troponin complex have?

A

4

19
Q

low Ca2+ ion concentration in muscle cells: (2)

A
  1. Ca2+ occupies up to 2/4 troponin binding sites
  2. tropomyosin and troponin complex inhibit binding of the myosis head to actin
20
Q

high Ca2+ ion concentration in muscle cells: (4)

A
  1. Ca2+ occupies all 4 troponin binding sites
  2. troponin complex changes conformation, slides tropomyosin away from myosin-actin binding site
  3. troponin complex moves out to allow binding of myosin head to actin
  4. cross-bridge forms between actin-myosin
21
Q

sarcoplasmic reticulum

A

specialised form of endoplasmic reticulum found in muscle cells, plays crucial role in regulation Ca2+ levels and muscle contraction

22
Q

how is a muscle cell stimulates? (8)

A
  1. alpha neuron action potential arrives at neuromuscular junction
  2. acetylcholine released from alpha neuron
  3. acetylcholine receptors in muscle cell activated
  4. action potential spreads along sarcolemma
  5. action potential invades T-tubules
  6. activation of T-tubules triggers sarcoplasmic reticulum to release Ca2+
  7. Ca2+ binds to troponin complex, allows myosin-actin cross-bridge to form
  8. cycle continues until Ca2+ concentration goes down
23
Q

how are smooth muscle cells regulated?

A

the autonomic nervous system

24
Q

smooth muscle cell structure compared to skeletal muscle cell (4)

A
  1. shorter
  2. contractile units diagonally arranged
  3. actin filaments arranged in upwards steps
  4. where actin thin filaments overlap, myosin thick filament placed
25
Q

how does myosin-actin interaction differ in smooth muscle cells?

A

myosin heads arranged in way where they pull actin to opposite directions (top/bottom of myosin)

26
Q

calmodulin

A

binds to 4 Ca2+ (like troponin)

27
Q

calmodulin activation at high Ca2+ concentration (4)

A
  1. Ca2+ molecules bind
  2. activates myosin light chain kinase (enzyme) in myosin head
  3. phosphorylation occurs triggering myosin head to bind to actin forming cross-bridge
  4. results in smooth muscle cell contraction

Physiology and Disease (13 decks)

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