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Physiology > Cardiovascular Physiology Smooth Muscle > Flashcards

Cardiovascular Physiology Smooth Muscle Flashcards

1
Q

where is smooth muscle found

A

around hollow organs such as blood vessels, airways, GI tract, uterus and fallopian tubes, ureters and bladder

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2
Q

what is smooth muscle important in

A

ocular function, piloerection

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3
Q

what can contraction of smooth muscle cause

A

propulsion or resistance

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4
Q

is stimulus for smooth muscle intrinsic or extrinsic

A

can be either

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5
Q

what is smooth muscle regulated by

A

autonomic neurons, hormones, and autocrine/paracrine signals

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6
Q

describe the smooth muscle cell

A

smaller cells with single central nucleus

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7
Q

describe the contraction of smooth muscle compared to skeletal muscle

A

-contractions are slower to develop
-contractions last significantly longer
-maximum force generation greater
-primarily oxidative metabolism

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8
Q

what is the shape of smooth muscle cells

A

elongated and tapered

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9
Q

does smooth muscle contain T tubules or SR

A

lacks T tubules and only has rudimentary SR

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10
Q

describe the duration of twitches between all 3 types of muscle

A

skeletal muscle is shortest and smooth muscle is the longest

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11
Q

what are the 2 types of smooth muscle

A

-multi unit
- single unit (unitary, visceral)

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12
Q

describe multi unit smooth muscle

A

-no gap junctions
-each cell responds independently
- muscle behaves as multiple units
-control exerted mainly by nerve signals
- cells function independently
- no tone

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13
Q

describe single unit smooth muscle

A

-cells connected by gap junctions
-functional syncytium
-control by variety of stimuli
- pacemaker cells
-cells organize into sheets or bundles
-may have tone

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14
Q

what are examples of multi unit smooth muscle

A

-piloerector muscle
-iris
- ciliary muscles

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15
Q

what are examples of single unit smooth muscle

A

gut
bladder
uterus

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16
Q

what is an example of a multi unit and single unit smooth muscle cell

A

blood vessels

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17
Q

what are the contractile elements of smooth muscle

A

actin and myosin

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18
Q

describe actin in smooth muscle

A

higher levels and longer than in skeletal/cardiac myocytes
- arranged diagonally to long axis of cell

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19
Q

what does alpha actinin attach to

A

actin to dense bodies instead of Z line

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20
Q

describe myosin in smooth muscle

A

-fewer myosin fibers than skeletal/cardiac myocytes
- myosin filaments interspersed with actin

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21
Q

what does calcium bind to in smooth muscle

A

calmodulin

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22
Q

what are the two actin binding proteins and what do each do

A
  • calponin: inhibits myosin ATPase
  • caldesmon: inhibits myosin/actin bond
23
Q

what needs to be removed from calcium in smooth muscle before contraction can occur

A

calponin and caldesmon

24
Q

is smooth muscle organized into sarcomeres

A

no

25
Q

what are the requirements for contraction in smooth muscle

A

-calcium
-ATP
-myosin light chain phosphorylation

26
Q

what is myosin light chain phosphorylation required for

A

myosin head to interact with actin

27
Q

what does myosin light chain kinase do

A

adds phosphate and begins contraction

28
Q

what does myosin light chain phosphatase do

A

removes phosphate and stops contraction

29
Q

what can smooth muscle contraction be stimulated by

A

-stretch
-ligands (NTs, hormones, paracrines, autocrines)
-intrinsic activity (pacemaker cells)

30
Q

where does calcium come from in smooth muscle

A

mostly extracellular and some intracellular

31
Q

are action potentials required for contraction

A

no or depolarization

32
Q

are smooth muscle cells tonic or phasic

A

tonic, they are normally contracted and can alter their force of contraction

33
Q

what is cross bridge cycling in smooth muscle controlled by

A

a calcium regulated enzyme that phosphorylates myosin

34
Q

what are the steps of contraction in smooth muscle

A
  • inactive calmodulin -> actin calcium calmodulin
    -inactive myosin light chain kinase -> active myosin light chain kinase
    -phosphorylation by myosin light chain kinase which forces cross bridge toward thin filament
  • cross bridge cycling
  • myosin light chain phosphatase dephosphorylates and stops contraction
35
Q

what are the two sources of calcium in smooth muscle

A

-the SR
- extracellular calcium entering the cell through plasma membrane calcium channels

36
Q

how is the calcium removed in smooth muscle

A

-to SR via calcium ATPase
- to ECF via calcium ATPase and sodium/calcium exchanger

37
Q

how do you vary the force of contraction in smooth muscle

A

alter the amount of calcium

38
Q

what is the latch state

A

tension is maintained in the smooth muscle although calcium levels and ATP usage in the cytosol are low

39
Q

what is the mechanism for how the latch state occurs

A

-binding of acetylcholine to muscarininc receptors
- increased influx of calcium into the cell
- activation of calmodulin dependent myosin light chain kinase
- phosphorylation of myosin
- increased myosin ATPase activity and binding of myosin to actin
-contraction
-dephosphorylation of myosin by myosin light chain phosphatase
-relaxation or sustained contraction due to the latch bridge and other mechanisms

40
Q

which muscle cells can be activated or inhibited

A

smooth muscle and cardiac muscle

41
Q

do smooth muscle neurons form synapses

A

no

42
Q

what do smooth muscle axons contain

A

varicosities

43
Q

where is the NT in smooth muscle released into

A

interstitial fluid

44
Q

how does the NT distribute to receptors on smooth muscle cell surfaces

A

via simple diffusion

45
Q

do hormones change membrane potential in smooth muscle

A

may or may not

46
Q

what is the difference between multiunit and single unit smooth muscle

A

mutli unit smooth muscle - each cell has its own activation
in single unit smooth muscle - theres only one signal to all cells

47
Q

what local factors cause smooth muscle activation

A

paracrine signals, acidity, O2, and CO2 levels, osmolarity and the ion composition of the ECF

48
Q

what does response to local factors do

A

alters smooth muscle contraction in response to changes in the muscles immediate internal environment, independent of long distance signals from nerves and hormones

49
Q

what local factor causes smooth muscle relaxation

A

nitric oxide

50
Q

what does stretching do locally to smooth muscle

A

cause response by contracting by opening mechanosensitive ion channels leading to membrane depolarization

51
Q

describe pacemaker potentials in smooth muscle

A

-resting membrane not stable, slow depolarization to threshold
-mechanism unknown

52
Q

where are smooth muscle pacemaker cells found

A

in GI tract

53
Q

what is the only type of muscle that has tone

A

single unit smooth muscle

54
Q

which muscle type is unaffected by hormones

A

skeletal

Physiology (41 decks)

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