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Cardio/Pulm Final > Lecture 2: Smooth Muscle Physiology > Flashcards

Lecture 2: Smooth Muscle Physiology Flashcards

1
Q

Histological appearance of skeletal muscle.

A

Large, multi-nucleated striated cells

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2
Q

Histological appearance of smooth muscle.

A

Smaller, single nucleus cells with NO striations

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3
Q

Sarcoplasmic reticulum of skeletal muscle

A

Large, WELL-developed SR with triads

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4
Q

Sarcoplasmic reticulum of smooth muscle

A

Poorly developed SR

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5
Q

Thin filament components of skeletal muscle

A

Actin, Tropomyosin, and troponin

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6
Q

Thin filament components of smooth muscle

A

Actin and Tropomyosin

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7
Q

Thick filament composition of skeletal muscle

A

Myosin with ATPase (faster activity)

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8
Q

Thick filament composition of smooth muscle

A

Myosin with ATPase (slow); myosin light chains

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9
Q

Which type of muscle contains more thin filaments; thick filaments?

A
  • Smooth = MORE thin (2x more)

- Skeletal = MORE thick (4x more)

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10
Q

As skeletal muscle is stretched, what happens to the ability to generate tension (force)?

A

Increased stretching = Decreased tension (force)

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11
Q

What 5 important functions must the muscle of the gut, vasculature, and respiratory tract be able to do?

A

1) Contract and maintain contraction for long period of time (energy efficient)
2) Contract periodically to mix contents of organ
3) Maintain shape of organ
4) Generate active tension even when stretched
5) Use relatively little ATP

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12
Q

Where is smooth muscle found?

A

1) Vasculature (arteries in particular)
2) GI tract
3) Urogenital tract
4) Respiratory tract
5) Eye

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13
Q

Where do the thin filaments of smooth muscle anchor?

A

Dense bodies

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14
Q

What do the different isoforms of myosin in smooth muscle contain?

A
  • Myosin light chain kinase

- Myosin light chain phosphatase

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15
Q

Is all smooth muscle the same?

A

No, because the needs are different based on where yo find smooth muscle, there ARE different types (although contractile mechanism is the same)

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16
Q

Where would you find smooth muscle with lots of gap junctions?

A
  • The gut

- Contraction is well coordinated

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17
Q

Where would you find more autonomous smooth muscle with less gap junctions?

A
  • Vasculature (arteries in particular)
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18
Q

Skeletal muscle is innervated by; using what neurotransmitter?

A
  • Alpha-motorneurons arising from spinal cord

- Acetylcholine

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19
Q

Intrinsic innervation of smooth muscle uses; is independent of?

A
  • Neurons (sensory and motor)

- Independent of CNS and PNS

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20
Q

What controls extrinsic innervation of smooth muscle; importance?

A
  • The autonomic nervous system

- Allows CNS to control viscera

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21
Q

How does acetylcholine act on smooth muscle?

A
  • Excites SOME smooth muscle (gut)

- May inhibit others (cause relaxation)

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22
Q

Norepi and epinephrine cause ______ of vascular smooth muscle?

A

Contraction

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23
Q

Norepi and epinephrine cause ______ of gut smooth muscle?

A

Inhibition

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24
Q

What neurotransmitter is the major inhibitor of smooth muscle?

A

Nitric Oxide (NO)

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25
Q

NO acts via what kind of mechanism?

A

cGMP mechanism

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26
Q

What is one of the major differences between skeletal and smooth muscle as far as neural control goes?

A

Smooth muscle CAN be DIRECTLY INHIBITED (caused to relax)

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27
Q

Where is neurotransmitter released from in smooth muscle?

A

Varicosities - swellings in the axon

28
Q

Skeletal muscle has only _______receptors for contraction?

A

Ach receptors

29
Q

NO does not require a membrane-bound receptor why?

A

Extremely lipid soluble; diffuses through cell membrane and has its action on the cGMP system

30
Q

Which 3 hormones are able to elicit smooth muscle contraction?

A

1) Acetylcholine
2) Epinephrine
3) Cholecystokinin (CCK)

31
Q

Another name for NO is?

A

Endothelium-derived relaxing factor (EDRF)

32
Q

Which agent can be released as both a NT and through paracrine mechanisms?

A
  • NO
33
Q

Stretching of some smooth muscle does what?

A

Another mechanism for activation

34
Q

What are the receptor types for skeletal muscle?

A

Nicotinic cholinergic

35
Q

What are the receptor types for smooth muscle?

A

Muscarinic cholinergic; Adrenergic, others

36
Q

What are the 2 sources of Ca2+ for smooth muscle contraction?

A

1) Sarcoplasmic reticulum

2) Extracellular sources

37
Q

The SR and Extracellular sources of Ca2+ are regulated ________ of one another.

A

Independently

38
Q

The binding of a hormone to a GPCR and subsequent activation of IP3 causes what in smooth muscles?

A

The release of Ca2+ from the SR

39
Q

What else is activated upon the creation of IP3 in smooth muscle?

A

PKC

40
Q

Why is the mechanism of using IP3 to release Ca2+ from the SR significant?

A

Smooth muscle can be activated to contract in the absence of an action potential

41
Q

What are the two type of channels for extracellular Ca2+ sources in smooth muscle?

A

1) Voltage-gated Ca++ channels

2) Ligand-gated Ca++ channels

42
Q

What is the importance of extracellular sources of Ca2+ in smooth muscle?

A

Allows for sustained contractions of smooth muscle

43
Q

What must occur for the myosin-ADP*Pi of smooth muscle to increase its affinity for the actin binding site?

A

Phosphorylation of the myosin light chain

44
Q

What’s step 1 for smooth muscle contraction?

A

Increase the intracellular calcium

45
Q

What occurs during step 2 of smooth muscle contraction?

A

Calcium will bind with Calmodulin

46
Q

What occurs during step 3 of smooth muscle contraction?

A

Calmodulin activates myosin light-chain kinase (MLCK)

47
Q

What occurs during step 4 of smooth muscle contraction?

A

MLCK phosphorylates the myosin light chain

48
Q

How does MLCK phosphorylate the myosin light chain?

A

Hydrolyzes a separate ATP —> ADP + Pi

49
Q

How many ATP are being used in smooth muscle contraction; location?

A

2 separate ATP; one on the light chain, and one on the myosin head

50
Q

What’s step 5 of of smooth muscle contraction?

A

Myosin cross bridge can begin cycle

51
Q

What occurs after the myosin forms a cross bridge with the actin binding site?

A

ADP + Pi will be released from the myosin head. A conformational change occurs and the power stroke is initiated

52
Q

The myosin head will stay bound to the actin binding site until?

A

An ATP comes in and binds to the myosin head proper, the myosin head will then dissociate back to the low affinity state

53
Q

During smooth muscle relaxation where is the calcium pumped and why?

A

Outside of the cell, because that is where most of it came from.

54
Q

What occurs once the calcium is taken off the calmodulin?

A

Calmodulin will inactivate the MLCK and we see the formation of a myosin light-chain phosphatase, which will remove the Pi from the myosin light chain and allow relaxation.

55
Q

The Pi can be removed from the myosin light chain at any point in the cycle - the cycle will then continue _______ and a new cycle ________. (latch mechanism)

A
  • Very slowly

- Cannot be started

56
Q

What occurs during the latch mechanism?

A
  • Dephosphorylation of the MLCK during cycle - slows cycle, especially at the binding of ATP (very slow).
  • Cross-bridges remain stuck (and therefore generating tension) for prolonged period of time
57
Q

With every stretch of smooth muscle cells what occurs with passive tension?

A

Increases a little, but as actin and myosin rearrange, the passive tension decreases again

58
Q

How are the thick and thin filaments arranged in smooth muscle?

A

Randomly! With far more thin filaments

59
Q

As smooth muscle is stretched, the myosin heads, once free from the actin, will interact with?

A

A DIFFERENT thin filament

60
Q

The “loose” arrangement of the thick and thin filaments allows them to ________ when the cell is stretched

A

Re-arrange

61
Q

The rearrangement of thick and thin filaments in smooth muscle allows for?

A

Passive tension to dissipate

62
Q

Why is the rearrangement in smooth muscle important for active tension?

A

Allows the cell to continue to develop active tension over a much wider range of lengths than we see in skeletal muscle

63
Q

Damage to blood vessels causes chemical signals to be released, which trigger smooth muscle to do what?

A

De-differentiate into fibroblasts

64
Q

Why is the de-differentiation of smooth muscle into fibroblasts important during injury?

A

Fibroblasts secrete the collagen needed to repair the damage

65
Q

What occurs to the fibroblasts once the damage is resolved?

A

They differentiate back into the smooth muscle cells required to make the blood vessel work properly

66
Q

What is the de-differentiation and differentiation of smooth muscle referred to as?

A

Plasticity

67
Q

Why is it crucial that smooth muscle can be intrinsically innervated independently of the CNS and PNS; paraplegic example?

A

In someone like a paraplegic, if the smooth muscle didn’t have intrinsic innervation they would not be able to do any kind of digestion

Cardio/Pulm Final (18 decks)

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