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Physiology > Smooth Muscle > Flashcards

Smooth Muscle Flashcards

1
Q

No _____ are seen in smooth muscle

A

sarcomeres

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2
Q

What is the actin/myosin ratio in smooth muscle

A

10:1

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3
Q

Intermediate filaments are cytoskeletal elements which form a structural backbone against which contraction occurs. ____ and ____ are 2 components of this cytoskeleton

A

desmin; vimentin

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4
Q

Dense bodies contain the protein ____ and are functionally analogous to Z-lines in striated muscle.

A

actinin

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5
Q

____ _____ allow direct electrical communications between adjacent smooth muscles

A

gap junctions

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6
Q

Smooth muscle contains no T-tubules and no terminal cistern system. This feature correlates with its small size and unique lack of what?

A

dependence on a muscle AP to induce contraction

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7
Q

In smooth muscle, the SR is poorly developed. Therefore, it is more dependent on _____ ____ for contraction

A

extracellular Ca2+

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8
Q

_____ is associated with smooth muscle actin. No ____ is associated with smooth muscle actin.

A

tropomyosin; troponin

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9
Q

Although _____ and ____ are actin binding proteins whose phosphorylation can modulate smooth muscle contraction by affecting ATPase activity, class thinking is that smooth muscle regulation differs from striated muscle regulation in that it is coupled to ____ levels through myosin-based mechanism

A

caldesmon; calponin; Ca2+

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10
Q

Myosin has ___ heavy chains and ____ light chains. Which ones serve an essential regulatory function in smooth muscle but probably not in striated muscle

A

2; 4; light chains

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11
Q

Smooth muscle myosin is thought to be organized in a ____-____ arrangement as opposed to a _____ arrangement seen for striated muscles.

A

side-polar; bipolar

note: this likely contributes to smooth muscles’s lack of well-defined sarcomeres

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12
Q

There are two types of smooth muscle units: single (visceral) and multiunit. Where is the single unit (visceral) subtype found?

A

small intestine, colon, uterus, urinary bladder, ureters, lymph vessels, smaller arterioles

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13
Q

Single unit smooth muscle tends to have many ____ _____ between cells. Innervation tends to be relatively ____

A

gap junctions; sparse

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14
Q

Slow wave potentials are associated with what subtype of smooth muscle?

A

single (visceral) unit

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15
Q

Single (visceral) unit smooth muscle shows this characteristic which allows slow stretch and lengthening of the muscle without a significant increase in pressure. ex: bladder filling up to a point

A

plasticity

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16
Q

This type of contraction is seen in single (visceral) unit smooth muscle. hint: think bladder

A

stretch induced contraction

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17
Q

In regards to multiunit smooth muscle, each smooth muscle cell acts relatively independently of other smooth muscle cells in the organ. In this sense, multiunit smooth muscle is like ____ muscle

A

skeletal

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18
Q

Where is the multiunit subtype of smooth muscle found?

A

ciliary muscle, iris, bronchial muscles, tracheal muscles, vas deferens, GI sphincters, and larger blood vessels

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19
Q

Multiunit smooth muscle tends to have less ___ ____ between cells making each cell operated independently. Multiunit smooth muscle tends to have higher _____ ratios than in visceral smooth muscle

A

gap junctions; innervation

20
Q

True or false, the membrane potential of multiunit smooth muscle is stable with no spontaneous depolarization

A

true

21
Q

Describe the effects of progesterone and estrogen on smooth muscle in pregnancy.

A

progesterone: reduces the number of gap junctions in myometrial smooth muscle, making it behave more like non-innervated multiunit smooth muscle, and render it relatively quiescent.
estrogen: causes smooth muscle hypertrophy and increase the number of gap junctions. This allows the muscle to behave more as a single unit smooth muscle and participate in parturition

22
Q

Intracellular calcium levels rise in smooth muscle to trigger contraction as in striated muscle. However, regulation occurs on the ____ filament, not in the ____ filament as in striated muscle.

A

thick (myosin); thin (actin-troponin-tropomyosin)

23
Q

In regards to smooth muscle contraction, Ca2+ binds Calmodulin ___:___

A

4:1

24
Q

The Ca2+/calmodulin complex binds to which kinase to form an active enzyme.

A

myosin light chain kinase

25
Q

The active Ca-calmodulin-MLCK enzyme complex phosphorylates a ___ residue of the myosin light chains associated with each myosin head. This phosphorylation requires ___ ATP and is essential to confer significant ___ activity on smooth muscle myosin

A

serine; 1; ATPase

26
Q

Myosin light chain phosphatase is continually removing the phosphates put on myosin light chains by active MLCK. If MLCK is inactive, what is the status of myosin? What about if MLCK activity is high?

A

MLCK inactive: myosin light chains are relatively dephosphorylated and MLCK has low ATPase activity

MLCK active: myosin is largely phosphorylated and MLCK has high ATPase activity

27
Q

MLCK activity is in correspondence to low and high ____ __ conditions

A

intracellular Ca2+

28
Q

In regards to MLCK activity, when does fact cycling and shortening of smooth muscle occur?

A

when MLCK/Phosphatase C activity ratio is high

29
Q

This is a special state that allows smooth muscle to maintain tone with a minimal expenditure of ATP. Shortening is not occurring.

A

latch state

30
Q

If myosin chains are dephosphorylated, myosin ATPase activity decreases. What does this mean in regards to the latch state?

A

it’s more difficult to release myosin heads from actin, which requires ATP hydrolysis - muscle can hold tone

31
Q

Why is efficiency low in smooth muscle?

A

because energy is required for both control and cross bridge cycling during shortening

32
Q

Why is economy high in smooth muscle?

A

because the ATP use is low to maintain force in the absence of external work - this is the latch state

33
Q

Low levels of phosphorylated myosin light chains cause _____

A

relaxation

34
Q

In regards to smooth muscle relaxation, Ca2+ is removed form the cell by the sarcolemmal ___/___ exchanger and a sarcolemmal ____ ATPase

A

3 Na+/Ca2+; Ca2+

35
Q

Phospholamban is a protein that normally inhibits the SR Ca2+ ATPase. Phosphorylation of phospholamban inhibits it. What would the result of this be?

A

Inhibiting the inhibiter -> promotion of Ca2+ sequestration - relaxation

36
Q

Resting membrane potential in smooth muscles is relatively positive, perhaps ____ mV

A

-55

37
Q

As in skeletal and heart muscle, changes in smooth muscle membrane potential can lead to contraction by opening voltage-sensitive Ca2+ channels. Unlike skeletal and hear muscle, ____-____ potentials as well as muscle ____ ____ can result in contraction

A

local-graded; action potentials

38
Q

Describe L-type Ca2+ channels

A

“L” is for long acting - channels open slowly and close slowly; affected by Ca2+ channel blockers

39
Q

Describe T-type Ca2+ channels

A

“T” is for transient - channels open and close quickly. Rapid influx from these channels may be key to Ca2+ induced Ca2+ release from SR, which is dependent on change of Ca2+ concentration, not absolute concentration

40
Q

Smooth muscle has relatively few of the voltage-gated ____ channels seen in other excitable cell types

A

Na+

41
Q

Describe cAMP-dependent relaxation

A

Protein Kinase A phosphorylates MLCK and prevents the calcium-calmodulin complex from activating it

42
Q

Describe cGMP-dependent relaxation

A

decrease in myosin light chain phosphorylation - may be due to increased phosphatase activity or decreased MLCK activity; changes are mediated through phosphorylation by cGMP-dependent protein kinase

43
Q

Describe PLC-dependent contraction

A

IP3 is formed and releases intracellular Ca2+ stores. DAG is also made and activates PKC which can phosphorylate an number of proteins that cause smooth muscle contraction

44
Q

In regards to ATP-sensitive K+ channels, ____ can decrease the intracellular [ATP], open these K+ channels, and hyper polarize the membrane

A

Ischemia

45
Q

In regards to ATP-sensitive K+ channels, _______ closes voltage gated, L-type Ca2+ channels, reduces Ca2+ influx, and relaxes the smooth muscle

A

hyperpolarization

46
Q

In regards to G-protein coupled K+ channels, agonsists (ACh) bind their receptors, causing receptor interaction with a G-protein of the ____ family

A

G alpha i

47
Q

The G alpha i subunit that is released directly, binds K+ channels and opens them. The cell _____, ___-___ Ca2+ channels are ____, and relaxation occurs

A

hyperpolarizes; L-type; closed

Physiology (7 decks)

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