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

L10: smooth muscle contraction & regulation Flashcards

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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?

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A

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

25
what is the antagonist pathway that regulates smooth muscle contraction? outline
``` antagonist cGMP PKG -ROCK +myosin phosphatase ```
26
what is the antagonist pathway that regulates smooth muscle contraction? describe
``` antagonist NT / receptor, increases cGMP, activates PKG protein kinase G, inhibits (phosphorylates -ROCK Rho Kinase, can't phosphorylate +myosin phosphatase ```
27
what does ROCK do in smooth muscle contraction?
phosphorylates myosin phosphatase, inhibiting it so it cannot dephosphorylate and inactivate myosin
28
what does PKG do in smooth muscle contraction?
phosphorylates ROCK so it can't phosphorylate (inhibit) myosin phosphatase, so contraction is inhibited
29
T/F the degree of contraction displayed by smooth muscle is the result of the balance of myosin phosphorylation and dephosphorylation reactions
true
30
list smooth muscle: regulatory pathway agonist pathway antagonist pathway
Ca+CAM+MLCK RhoA+ROCK-MyosinPhosphatase cGMP+PKG-ROCK+MyosinPhosphatase
31
which muscle type is capable of a latch state?
smooth muscle
32
what is latch state in smooth muscle contraction?
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
what is the mechanism of the latch state?
unkown... could be that myosin cross bridges are dephosphorylated while they are still attached
34
T/F all muscles can be stretch activated
true | but smooth muscle is the most-so
35
what is stretch activation of muscle
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
T/F stretch-activated channels are highly selective
false | non-selective (Na+, K+, Ca++, Mg++)
37
outline the mechanism of stretch activation
``` stretch/distension non-selective channels (Na,K,Ca,Mg) VGchannels & depolarization Ca++ influx contraction ```
38
when is a smooth muscle wall subject to stress relaxation?
when stretch is not enough to cause contraction... wall tension initially rises, then drops due to visco-elastic properties
39
visceral smooth muscle cells are A. single unit B. multi unit
``` single unit (like a functional syncytium) ```
40
T/F the distinction between single and multiunit smooth muscle types is incomplete and there is overlap between the two categories
true
41
which can exhibit pacemaker activity A. single unit smooth muscle B. multi unit smooth muscle
single unit smooth muscle
42
describe pacemaker activity
spontaneous electrical activity from pacemaker cells is transmitted by intercellular electrical junctions which lead to contractile activity as a "single unit"
43
what is a BER
a basic electrical rhythm, or slow wave
44
what causes a BER
basic electrical rhythm is thought to result from cyclic changes in ion conductances of pacemaker cells
45
is the slow wave BER by itself enough to reach threshold and cause action potentials?
it may be, or it may not be, depending on the pacemaker | will be subject to modulation either way
46
in pacemaker activity, what determines: contraction force contraction frequency
force dependent on frequency of spike activity | frequency dependent on BER (phase-locked)
47
T/F pacemaker activity is phase-locked
true | it is dependent on the BER basic electrical rhythm
48
smooth muscle pacemaker is __ in origin, but __ in modulation
myogenic in origin | neurohormonal in modulation
49
what modulates pacemaker activity?
neurohormonal input
50
T/F slow waves may be associated with different numbers of action (spike) potentials
true | depending on neurohormonal input
51
T/F slow waves and action (spike) potentials arise from different membrane mechanisms
probably true, not fully known
52
what is the myenteric plexus
a plexus of nerves associated with the enteric smooth muscle nervous system -this is where vagal efferent fibers synapse with the GI tract
53
where do vagal efferent fibers synapse with the GI tract?
at the myenteric plexus
54
parasympathetic (usually cholinergic) stimulation on the myenteric plexus is usually...
excitatory and causes depolarization and motor activity
55
sympathetic (usually adrenergic) stimulation on the myenteric plexus is usually...
inhibitory (less motor activity)
56
parasympathetic stimulation on the myenteric plexus is usually A. cholinergic B. adrenergic
cholinergic
57
sympathetic stimulation on the myenteric plexus is usually A. cholinergic B. adrenergic
adrenergic
58
how can a smooth muscle subject to a BEG basic electrical rhythm achieve large contractile forces?
action (spike) potentials on successive slow waves can summate (usually like unfused tetanus)

Physiology 1 (WPH) (18 decks)

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