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Cells to Tissues > Smooth muscle > Flashcards

Smooth muscle Flashcards

1
Q

What are the 2 categories of smooth muscle?

A
  1. Unitary or visceral connected by low resistance gap junctions and act as a functional syncitium.
  2. Multiunit smooth muscle, a collection of NOT interconnected cells.
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2
Q

Describe smooth muscle actin and myosin organization.

A

Mostly disordered with dense bodies (kinda like z lines) and dense plaques (like focal adhesions)

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3
Q

What are 3 types of actin in smooth muscle?

A

alpha and gamma (contractile) and beta (cytoplasmic)

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4
Q

Unlike skeletal muscle which has bipolar myosin filaments, smooth muscle myosin is _____-polar.

A

Side-polar, which allows complete cross over of filament on one side.

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5
Q

Why can smooth muscle thin filaments shorten so extensively?

A

Filaments are quite a bit longer and the lack of z line means filaments aren’t limited by the length of a sarcomere and can overlap extensively.

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6
Q

What ways can Ca2+ enter the smooth muscle cell to trigger contraction?

A
  1. Voltage/ligand gated channel
  2. Ryanodine calcium receptor (+ feedback)
  3. IP3 gated calcium channel
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7
Q

How is myosin activity regulated in smooth muscle?

A

Phosphorylation. No troponin/tropomyosin!!

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8
Q

How does the myosin kinase (MLCK) get activated?

A

4Ca2+ calmodulin binding

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9
Q

How does calcium affect myosin-dephosphorylation (contractility agonist)?

A

See pic

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10
Q

How does protein kinase G act as a contractility antagonist?

A

see pic

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11
Q

What are tonic vs phasic smooth muscles?

A

Tonic expend little energy and can stay contracted for ages (e.g. artery) while phasic consume a lot (e.g. GI contraction/relaxation)

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12
Q

How do tonic muscles maintain contraction?

A

Latch state: modification of the crossbridge cycle, possibly by dephosphorylation of crossbridges while they are still attached to actin.

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13
Q

What is stretch-activation and how does it work?

A

When smooth muscle is stretched, it automatically contracts most likely via stretch-activated channels that lead to depolarization.

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14
Q

When SM stretch is insufficient to reach threshold, it relaxes (stress-relaxation). What property is this an example of?

A

Visco-elasticity

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15
Q

Are multiunit or single unit smooth muscles governed by pacemakers?

A

Single unit. Multinuit are innervated individually.

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16
Q

Are increased electrical spikes (higher frequency) associated with greater muscle tension in SM?

A

Yes

17
Q

What is peristalsis?

A

The gradual, wavelike contraction typical of smooth muscle

18
Q

How does tension change in smooth muscle?

A

The tone/tension can vary and they’re never truly contracted or relaxed.

19
Q

Smooth muscle can contract down a ____% of their original length.

A

Major, due to structure of SM.

20
Q

The velocity of smooth muscle contraction is quite _____, because ATP is split _______ by the myosin isozyme (myosin ATPase).

A

slow, slower,

21
Q

What are 6 important properties of smooth muscles?

A
  1. High % contraction
  2. Slow contraction
  3. Vary tone
  4. Latch (maintain tone w/out energy expenditure)
  5. Stretch activation
  6. Pacemaker
22
Q

How do SMs vary tone so well?

A

No troponin, use signal transduction instead

23
Q

Can smooth muscles achieve the same level of maximum force as skeletal muscle?

A

Yes, smooth muscles are economical (slow/less ATP) but can be just as strong

24
Q

Can the MLCK function in the absence of calcium-calmodulin?

A

No!

25
Q

How does cAMP affect relax the muscle?

A

Activates PKA which increases calcium sequestration and thus relaxation.

26
Q

Does activation of beta receptors increase or decrease smooth muscle contractility?

A

Decrease

27
Q

Does activation of alpha receptors increase or decrease smooth muscle contractility?

A

Increase

28
Q

What is the action of rho kinase?

A

Phosphorylates the phosphatase and diminishes its activity. This will lead to longer A-M binding and increase contractility!

29
Q

How does cGMP affect contractility?

A

Activates protein kinase G (PKG) which inhibits Rhokinase ultimately leading to LESS contraction.

30
Q

How does NO affect contractility?

A

Decreases contractility by activating cGMP.

31
Q

How does calcium act in the latch mechanism?

A

Once tension is reached, calcium rises with tension but then falls down to some super basal level but NOT zero.

32
Q

What part of myosin is unstable in aqueous environments?

A

Single chain helices (part of the flexible lever arm). Stabilized by phosphorylation

33
Q

What happens to myosin if not stabilized by phosphorylation?

A

Myosin heads stick to each other and bind to their own thick filament

34
Q

When stretch activated channels are activated, what enters the cell?

A

Positively charged ions causing local depolarization which can open nearby voltage-gated channels

Cells to Tissues (23 decks)

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