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Medical Physiology > Smooth Muscle Contraction > Flashcards

Smooth Muscle Contraction Flashcards

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USMLE® Step 1 flashcards
1
Q

how is smooth muscle regulated

A

both neural and hormonal control systems

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2
Q

what is phasic smooth muscle

A

produce transient contractions associated with AP, rhythmic contractions, may contract intermittently during voluntary control

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3
Q

what is tonic smooth muscle?

A

produce sustained contraction - hold tension, then relax and then hold again

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4
Q

what is single unit smooth muscle

A

bunch of cells electrically coupled so that potential changes and contraction spread throughout the muscle – acting like a single unit

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5
Q

what is multi unit smooth muscle

A

not electrically coupled, so act independently

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6
Q

examples of phasic muscle

A
  1. stomach and intestines - rhythmic contraction

2. esophagus and urinary bladder - intermittent contraction during swallowing or urination

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7
Q

examples of tonic muscle

A
  1. sphincters - hold tension and then relax

2. blood vessels and airways - normally contracted and generate variable stready state force

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8
Q

describe autonomic nerves

A

have varicosities rather than synapses (widening of the cell where it releases NT)

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9
Q

how is info carried to CNS?

A

afferent

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10
Q

what intrinsic innervation do organs have?

A

local networks to regulate even if ANS is out, like meissner and auerbach plexus’ !

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11
Q

how is smooth muscle velocity regulated?

A

phosphorylation of myosin light chains! regulated by calmodulin

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12
Q

what controls force of contraction and velocity in smooth muscle?

A

percentage of myosin light chain phosphorylation and Ca level

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13
Q

what happens with increased phosphorylation of myosin light chains?

A

increase contraction and velocity

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14
Q

how are number of active crossbridges regulated in smooth muscle?

A

calcium level and phosphorylation of myosin

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15
Q

what does myosin phosphatase do?

A

dephosphorylates myosin light chains - no new crossbridge attachments

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16
Q

when does force increase?

A

Ca-Calmodulin complex makes MLCK more active than MP

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17
Q

how does sm muscle relax?

A

MP more active than MLCK

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18
Q

how can calcium concentration be increased in smooth muscle?

A

HORMONES and NT

  1. depolarization - opens vg ca channels
  2. IP3 - Ca release from SR
  3. hormones/NT - open ligand gated Ca channels
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19
Q

what occurs when calcium concentration increase

A

more Ca binds to calmodulin

20
Q

what occurs when there are more Ca-calmodulin complexes?

A

increased MLCK activity – increased phosphorylation of MLC and more cross bridges

21
Q

describe tonic contraction

A

slow cycling, long attachment (covalent attachment of phosphorylation of MLCK), conserves energy

22
Q

how is SR controlled in smooth muscle?

A

chemically via hormonal signals and 2nd messengers

23
Q

how is SR controlled in cardiac muscle

A

chemical and electrical control

24
Q

why is 2nd messenger system needed for Ca release from SR?

A

SR is not connected to membrane by T tubule system, so electrical control doesn’t work

25
Q

what is the calcium increase that triggers contraction?

A
  1. influx of Ca across sarcolemma

2. 2nd msgr mediated SR release

26
Q

how is sustained contraction of smooth muscle cells achieved?

A

influx of Ca from ECF

27
Q

how does Ca influx

A
  1. receptor activated

2. potential dependent

28
Q

describe how second messenger systems increase Ca

A
  1. phospholipase C PLC produces IP3 and DAG
  2. IP3 opens Ca channels of SR
  3. Rho kinase phosphorylates MP, reducing activity
  4. Rho kinase turns on CPI 17 which inhibits MP
  5. increased free Ca and decreased phosphatase activity
  6. increased force and velocity
29
Q

what occurs if potassium conductance is increased?

A

K leaves the cell and the cell hyperpolarizes, reducing Ca channels open and reducing Ca influx, reducing force

30
Q

what inhibitory receptors reduce Ca influx?

A

potassium conductance

31
Q

what occurs if K conductance is decreased

A

cell depolarizes, opening Ca channels and increasing Ca influx.

32
Q

what effect does cAMP or cGMP have on the cardiac cell?

A

relaxation, cAMP phosphorlyates MLCK and reduces its activity and reduces Ca concentration, therefore making relax

33
Q

why does NO promote dilation/relaxation of smooth muscle?

A

NO increases cGMP, which reduces MLCK and [Ca], reducing force

34
Q

explain why vasodilation happens while skeletal muscle contracts

A

skeletal muscle releases NO during contraction which changes tissue metabolic activity and changes blood flow to the tissue!!!!! active tissue releases NO, which promotes relaxation of blood vessel smooth muscle, increasing blood flow to that area c

35
Q

contrast cGMP decrease in heart vs smooth muscle

A

decrease in cGMP in heart would decrease force, decrease cGMP in smooth muscle increases force

36
Q

what does Rho kinase do

A

inhibits MP, which increases phosphorylated MLC and increases force

37
Q

what occurs during vasospasm

A

IP3 turns on Rho kinase, which inhibits MP, RhoA activated by GTP stimulates ROK which phosphorylates MP and turns on CPI17, increasing calcium and cross bridge

38
Q

effect, receptor and signal of NE

A

NE binds to alpha1 adrenergic receptors and causes contraction via IP3

39
Q

effect, receptor, signal of Epi

A

epi binds to B2 adrenergic receptors and causes relaxation via cAMP (increased cAMP decreases force)

40
Q

what sympathetic receptors in heart

A

beta1 adrenergic (increase in cAMP increases force)

41
Q

effect, receptor and signal Ach

A
  1. acts on muscarininc 3 receptors on smooth muscle cells to cause contraction via IP3
  2. acts on M3 on endothelial cells to cause relaxation due to NO
42
Q

effect recetpro signal Angiotensin II

A

works on AT-II receptors to contract via IP3

43
Q

effect receptor signal ADH/vasopressin

A

works on AVPR1A (V1) receptors to cause contraction via IP3

44
Q

effect receptor signal endothelin

A

binds to endothelin receptor to cause contraction via IP3

45
Q

effect receptor signal adenosine

A

binds to adenosine receptor to cause relaxation due to cAMP

46
Q

what occurs in hypercalcemia

A
  1. flaccid paralysis in skeletal muscle bc blocks v.g. Na channels and holds them in fixed position
  2. increases force of contraction of cardiac and smooth muscle

Medical Physiology (21 decks)

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