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Physiology 1 (WPH) > L10: smooth muscle contraction & regulation > Flashcards

L10: smooth muscle contraction & regulation Flashcards

1
Q

what is a single unit smooth muscle

A

cells connected by gap junctions so that tissue behaves as a syncytium
(e.g. uterus, ureters, GI tract)

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2
Q

what is a multi unit smooth muscle

A

collection of individual cells not interconnected, individually innervated, and contract independently
(e.g. iris of eye)

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3
Q

this muscle type uses ATP most economically

A

smooth muscle

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4
Q

this muscle type has slower cross-bridge cycling rate

A

smooth muscle

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5
Q

what anchors actin filaments in smooth muscle cells?

A

dense bodies aka dense plaques aka focal adhesions (when on cell membrane)

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6
Q

T/F dense bodies can be adhered to membrane or located more centrally in the cytosol

A

true

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7
Q

the smooth muscle analogue of z-lines are

A

dense bodies

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8
Q

what is the main protein in dense bodies

A

α actinin

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9
Q

two types of contractile actin include

A

α and γ

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10
Q

cytosolic / cytoskeletal actin is of this form

A

β

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11
Q

in smooth muscle:
α actin
β actin
γ actin

A

α actin - contractile
β actin - structural / cytosolic
γ actin - contractile

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12
Q

to what percentage of rest length can a smooth muscle cell contract?

A

~30% of rest length

thanks to side polarity of myosin, no z lines

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13
Q

what structural features allow smooth muscle to contract to shorter proportions than skeletal and cardiac muscle?

A

side polarity of thick filaments

no z-lines

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14
Q

T/F thin filaments in smooth muscle are longer than those in skeletal muscle

A

true

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15
Q

how is smooth muscle contraction regulated? outline

A 
Ca++
calmodulin
MLCK
MLC
myosinPi is active cycles with actin
-Ca++
- 4Ca++calmodulin
-MLCK
-myosin phosphorylation
-actin myosin cross bridge cycling
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16
Q

how is smooth muscle contraction regulated? describe

A 
t-tubule DHPR releases Ca++
Ca++ activates SR Ca++ release from RYR2
4Ca++ bind Calmodulin
4Ca++Calmodulin bind MLCK
44Ca++CalmodulinMLCK phosphorylate MLC
myosinPi is active cycles with actin
-Ca++
- 4Ca++calmodulin
-MLCK
-myosin phosphorylation
-actin myosin cross bridge cycling
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17
Q

T/F both smooth and skeletal muscle contraction are regulated by Ca++

A

true

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18
Q

T/F smooth muscle has troponin

A

false

no troponin, only non-inhibitory tropomyosin

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19
Q

T/F smooth muscle has tropomyosin

A

true

though non-inhibitory as there is no troponin

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20
Q

myosin light chain kinase in smooth muscle is controlled by…

A

Ca++CAM

calcium-calmodulin complex

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21
Q

what is the agonist pathway that regulates smooth muscle contraction? outline

A

agonist
RhoA
ROCK
- myosin phosphatase

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22
Q

what is the agonist pathway that regulates smooth muscle contraction? describe

A

agonist NT / receptor, activates
RhoA GTPase, activates
Rho Kinase, phosphorylates (inhibits)
- myosin phosphatase

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23
Q

what is the function of myosin phosphatase?

A

dephosphorylate myosin in smooth muscle so it is no longer active to bind to actin

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24
Q

what is the function of MLCK?

A

phosphorylate myosin regulatory light chains (proximal) so it is active to bind to actin

25
Q

what is the antagonist pathway that regulates smooth muscle contraction? outline

A 
antagonist
cGMP
PKG
-ROCK
\+myosin phosphatase
26
Q

what is the antagonist pathway that regulates smooth muscle contraction? describe

A 
antagonist NT / receptor, increases
cGMP, activates
PKG protein kinase G, inhibits (phosphorylates
-ROCK Rho Kinase, can't phosphorylate
\+myosin phosphatase
27
Q

what does ROCK do in smooth muscle contraction?

A

phosphorylates myosin phosphatase, inhibiting it so it cannot dephosphorylate and inactivate myosin

28
Q

what does PKG do in smooth muscle contraction?

A

phosphorylates ROCK so it can’t phosphorylate (inhibit) myosin phosphatase, so contraction is inhibited

29
Q

T/F the degree of contraction displayed by smooth muscle is the result of the balance of myosin phosphorylation and dephosphorylation reactions

30
Q

list smooth muscle:
regulatory pathway
agonist pathway
antagonist pathway

A

Ca+CAM+MLCK
RhoA+ROCK-MyosinPhosphatase
cGMP+PKG-ROCK+MyosinPhosphatase

31
Q

which muscle type is capable of a latch state?

A

smooth muscle

32
Q

what is latch state in smooth muscle contraction?

A

stimulus ends
Ca++ decreases
myosin ATPase stops working
*BUT myosin crossbridges remain attached for long periods of time, allowing tension holding without ATP consumption
(mechanism unknown… may result from dephosphorylation of myosin cross bridges before they detach)

33
Q

what is the mechanism of the latch state?

A

unkown… could be that myosin cross bridges are dephosphorylated while they are still attached

34
Q

T/F all muscles can be stretch activated

A

true

but smooth muscle is the most-so

35
Q

what is stretch activation of muscle

A

thought to result from membrane conductance changes in specific stretch-activated channels that lead to depolarization and contraction independent of neurohormonal influences
(most in smooth muscle, but present in all muscle)

36
Q

T/F stretch-activated channels are highly selective

A

false

non-selective (Na+, K+, Ca++, Mg++)

37
Q

outline the mechanism of stretch activation

A 
stretch/distension
non-selective channels (Na,K,Ca,Mg)
VGchannels & depolarization
Ca++ influx
contraction
38
Q

when is a smooth muscle wall subject to stress relaxation?

A

when stretch is not enough to cause contraction… wall tension initially rises, then drops due to visco-elastic properties

39
Q

visceral smooth muscle cells are
A. single unit
B. multi unit

A 
single unit
(like a functional syncytium)
40
Q

T/F the distinction between single and multiunit smooth muscle types is incomplete and there is overlap between the two categories

41
Q

which can exhibit pacemaker activity
A. single unit smooth muscle
B. multi unit smooth muscle

A

single unit smooth muscle

42
Q

describe pacemaker activity

A

spontaneous electrical activity from pacemaker cells is transmitted by intercellular electrical junctions which lead to contractile activity as a “single unit”

43
Q

what is a BER

A

a basic electrical rhythm, or slow wave

44
Q

what causes a BER

A

basic electrical rhythm is thought to result from cyclic changes in ion conductances of pacemaker cells

45
Q

is the slow wave BER by itself enough to reach threshold and cause action potentials?

A

it may be, or it may not be, depending on the pacemaker

will be subject to modulation either way

46
Q

in pacemaker activity, what determines:
contraction force
contraction frequency

A

force dependent on frequency of spike activity

frequency dependent on BER (phase-locked)

47
Q

T/F pacemaker activity is phase-locked

A

true

it is dependent on the BER basic electrical rhythm

48
Q

smooth muscle pacemaker is __ in origin, but __ in modulation

A

myogenic in origin

neurohormonal in modulation

49
Q

what modulates pacemaker activity?

A

neurohormonal input

50
Q

T/F slow waves may be associated with different numbers of action (spike) potentials

A

true

depending on neurohormonal input

51
Q

T/F slow waves and action (spike) potentials arise from different membrane mechanisms

A

probably true, not fully known

52
Q

what is the myenteric plexus

A

a plexus of nerves associated with the enteric smooth muscle nervous system
-this is where vagal efferent fibers synapse with the GI tract

53
Q

where do vagal efferent fibers synapse with the GI tract?

A

at the myenteric plexus

54
Q

parasympathetic (usually cholinergic) stimulation on the myenteric plexus is usually…

A

excitatory and causes depolarization and motor activity

55
Q

sympathetic (usually adrenergic) stimulation on the myenteric plexus is usually…

A

inhibitory (less motor activity)

56
Q

parasympathetic stimulation on the myenteric plexus is usually
A. cholinergic
B. adrenergic

A

cholinergic

57
Q

sympathetic stimulation on the myenteric plexus is usually
A. cholinergic
B. adrenergic

A

adrenergic

58
Q

how can a smooth muscle subject to a BEG basic electrical rhythm achieve large contractile forces?

A

action (spike) potentials on successive slow waves can summate (usually like unfused tetanus)

Physiology 1 (WPH) (18 decks)

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