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Fundamentals in pharmacology and physiology > Contractile mechanisms > Flashcards

Contractile mechanisms Flashcards

1
Q

What are the three types of muscles?

A

Skeletal
Cardiac
Smooth

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2
Q

What is contraction?

A

Contraction is the interaction of actin and myosin fueled by ATP and driven by rise in [Ca2+]

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3
Q

Skeletal vs Cardiac vs Smooth

Striation

A

Smooth not striated whereas skeletal and cardiac are

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4
Q

Skeletal vs Cardiac vs Smooth

A

Skeletal have many nucleus

Cardiac usually have one nucleus

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5
Q

What do both skeletal and cardiac muscles have?

A

Have T-tubules

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6
Q

What are T-tubules?

A

T-tubules are cell membranes that extend deep into cell interior

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7
Q

What do T-tubules interact with?

A

Interact with sarcoplasmic reticulum

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8
Q

How are skeletal muscles organised?

A

Thick filaments made up of myosin
Thin filaments made up of actin
Where two filaments overlap, seen as dark region

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9
Q

What is depolarization initiated by?

A

Depolarisation initiated by nAchr

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10
Q

What is depolarization maintained by?

A

Maintained by Na+ channels

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11
Q

What is there within the T-tubules?

A

Within t-tubules, there are voltage sensing ion channels like proteins which physically interact with Ca2+ in sarcoplasmic reticulum

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12
Q

What is the calcium release channel called?

A

Ryanodine receptor

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13
Q

What do ryanodine receptors interact with?

A

Ryanodine receptors interact with DHP

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14
Q

What are DR channel proteins?

A

Ion channel that doesn’t conduct ions

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15
Q

Why are DR channels known as this?

A

So called because it is blocked by DHP that are well known calcium channel blockers

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16
Q

Brief overview of contractile mechanism

A

Tropomyosin lying on actin covering myosin binding site

Calcium binds to troponin and conformational change occurs and myosin binding site on actin is exposed

17
Q

Contractile cycle(Priming of myosin head)

A

ATP hydrolysed by ATPase present on myosin head

Cocking of myosin head

18
Q

Contractile cycle(Power stroke with actin)

A

Power stroke occurs and ADP is released
Myosin undergoes conformational change
Actin moves towards centre of sarcomere

19
Q

Contractile cycle(Relaxation of acto-myosin complex

A

ATP binds to myosin head causing cross bridge to break and myosin head detaches from actin

20
Q

How does contraction occur in cardiac muscles?

A

Ion channels in T-tubules pump out Ca2+ into cell
Increased [Ca2+] results in calcium induced calcium release from RyR2
Lead to contraction

21
Q

Skeletal vs Cardiac

A

Skeletal:Physical interaction between DHP and RyR
Cardiac:Opening calcium channel promotes CICR

22
Q

What are smooth muscles not in?

A

Contractile proteins not in regular arrays:

Not striated

23
Q

What do smooth muscles not have?

A

Don’t have a T-tubule system

24
Q

Smooth muscles have a less developed…

A

Less developed SR

25
Q

What are smooth muscles able to sustain?

A

Sustain contraction for longer periods

26
Q

What do myofilaments in smooth muscle connect with?

A

Myofilaments connect with dense bodies

27
Q

What is present instead of troponin?

A

No troponin but caldemson and calponin

28
Q

What does tropomyosin not interact with?

A

Tropomyosin doesn’t interact with myosin binding site

29
Q

Difference between the myosin in smooth and skeletal muscles

A

Myosin in smooth muscles is a different isoform than skeletal muscles

30
Q

What does myosin have a lower of?

A

Lower ATPase activity

Lower affinity for ATP

31
Q

Contraction of smooth muscle

A

Increased calcium
Calcium binds to calmadulin
Activates myosin light chain kinase which phosphorylates myosin at light chain

32
Q

What does activation of myosin light chain kinase do?

A

Phosphorylates regulatory MLC at Ser 19
Increases ATPase activity of myosin lead by 1000x
Alters structure of myosin

33
Q

Relaxation of smooth muscle and comment on the dephosphorylatoin of myosin

A

[Ca2+] drops
MLCK becomes inactive
MLCP removes phosphate from Ser 19
But dephosphorylated myosin has a low ATP affinity
Latch state and slow release of actin from myosin

34
Q

Smooth muscle vs skeletal muscle

A 
Greater shortening in smooth
Slower speed of contraction in smooth
Lower energy requirement in smooth
Greater force generation in smooth
Latch state due to myosin having low ATP affinity

Fundamentals in pharmacology and physiology (15 decks)

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