Phys - Smooth Muscle Flashcards Preview

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Flashcards in Phys - Smooth Muscle Deck (59):
1

What is missing in smooth muscle?

Sarcomeres
T-tubules or terminal cisternae

SR is poorly developed
-still functions, but extracellular Ca++ is needed

2

Caldesmon and Calponin

Actin binding proteins that are modulatory of ATPase

Probably not primary control proteins

3

Unlike skeletal muscle, smooth muscle does not have which troponin unit?

Troponin I

4

Classification of smooth muscle units

Single unit (visceral or unitary)

Multi unit

5

Single unit smooth muscle characteristics

Behaves in a syncytial manner
-All the cels of the single unit act together

Tends to have many gap junctions

Relatively sparse innervation

6

Organs with single unit smooth muscles

Small intestine
Colon
Bladder
Uterus
Ureters

Lymph vessels
Precapillary sphincters

7

Do single unit smooth muscles have fast or slow wave potentials?

Slow
Sometimes cause contractions, sometimes do not


8

Action potentials of single unit smooth muscles

Spikes

All or none
Almost always contraction
More spikes = stronger contraction

9

Slow stretch vs fast stretch of single unit smooth muscle

Slow = lengthening
-ex: bladder capacity w/o pressure increase
-plasticity or stress relaxation

Fast = contraction
-ex: smallest arterioles or precapillary sphincters

10

Organs with multi unit smooth muscle

Ciliary muscle
Iris
Tracheal muscle
Bronchial muscle
GI sphincter
Vas deferens

Resistance vessels
Larger arterioles

11

Multi unit smooth muscle characteristics

Each cell acts independently (like skeletal muscle)

Less gap junctions

Higher innervation ratios than single unit

12

True or false: multi unit smooth muscle does not have action potentials.

True
Typically

13

High progesterone effect of smooth muscle

Reduce gap junctions in myometrial smooth muscle during pregnancy

-causes myometrium to behave more like non-innervated multiunit smooth muscle

-myometrial muscle remains relatively inactive/dormant/quiescent

14

Effects of rising estrogen levels on smooth muscle

Hypertrophy

Increase gap junctions

Myometrial behaves more like a single unit
-parturition

15

Morning sickness is caused by__

Reduced number of gap junctions by high levels of progesterone

16

High levels of cAMP cause __

Relaxation

by lowering MLCK concentration

17

In smooth muscle latch state:
Efficiency is ___
Economy is ___

Efficiency is low
ATP required for control and cross bridge cycling

Economy is high
Absence of shortening
Maintain tone with minimal use of ATP

18

Na+ / Ca++ exchanger

3 Na+ / Ca++

19

Phospholamban inhibits __

Ca++ ATPase

Phosphorylation of PLB relaxes

20

Testing membrane potential of smooth muscle

-55 mV

Due to high Na+ leak

Inward Ca++ current

21

Smooth muscle has (a lot of, or few) voltage-gated Na+ channels?

Few

- fast channels

22

L-type Ca++ channels

Long acting
Slow

Depolarization: ⬆️ intracellular Ca++

Hyperpolarization: ⬇️ intracellular Ca++

Can be blocked by Ca++ channel blockers

23

T-type Ca++ channels

Fast
Not blocked by Ca++ channel blockers

24

How is smooth muscle unique in activation?

Neurotransmitters, hormones, and drugs can lead to contraction and relaxation

25

cAMP causes PKA-dependent phosphorylation of ___ which causes __

Phospholamban

Increased Ca++ reuptake at the SR

RELAXATION

26

NO and ANP are part of

cGMP-dependent relaxation

Decreased myosin light chain phosphorylation

27

IP3 actions

Releases intracellular Ca++ stores

28

PLC-dependent contraction is mediated by __

Gq (m1,3,5 and alpha 1 adrenergic)

29

DAG activates __

PKC

Phosphorylates myosin light chains?
L-type Ca++ channel phosphorylation

30

ATP sensitive K channels
When are the closed?
Open? Mechanism?

Closed when [ATP]i is normal

Opens in ischemia (⬇️ ATP)
- K+ influx = hyperpolarization
- voltage sensitive Ca++ channels close
- intracellular Ca++ decreases
- smooth muscle relaxes

31

Ligand operated G protein coupled K channels - mechanism

Agonists :
ACh, m2
Adenosine, A1


Activates G alpha 1 type G protein

G alpha 1 binds IK(ACh) channel
K+ channels open
K+ efflux
Hyperpolarization
L-type Ca++ channels close
Relaxation occurs

32

Intermediate filaments of smooth muscle
2 protein components

Desmin
Vimentin

33

Dense bodies contain ___
These are functionally analogous to ___
They anchor __

Actinin
Z lines
Actin

34

____ allow communication between adjacent smooth muscle cells

Gap junctions and
Mechanical junctions

35

Smooth muscle contains no __

T tubules
Terminal cisternae
Sarcomeres
Troponin

36

Actin/myosin ratio in skeletal vs smooth muscle

Skeletal 2:1
Smooth 10:1

37

Actin binding proteins whose phosphorylation can affect ATPase and modulate smooth muscle contraction

Caldesmon
Calponin

38

Light chains serve and essential regulatory function in ___ muscle but not ___ muscle

Smooth
Skeletal

39

Smooth muscle myosin is thought to be organized in a ___ arrangement whereas skeletal is ___

Side-polar
Bipolar

*contributes to smooth muscles lack of well defined sarcomeres

40

What type of smooth muscle is
Small intestine

Single unit/Visceral

41

What type of smooth muscle is
Uterus

Single unit:Visceral

42

What type of smooth muscle is
Ciliary muscle
Iris muscle

Multi unit

43

What type of smooth muscle is
1. Large blood vessels
2. Small blood vessels
3. Lymph vessels

1. Multi unit
2-3. Single unit/Visceral

44

What type of smooth muscle is
Colon

Single unit/visceral

45

What type of smooth muscle is
Urinary bladder
Ureters

Single unit/visceral

46

What type of smooth muscle is
Bronchial muscle
Trachial muscle

Multi unit

47

What type of smooth muscle is
GI sphincters

Multi unit

48

What type of smooth muscle tends to have many gap junctions and sparse innervation?

Single unit/visceral

49

True or false:
Multi unit smooth muscles do not typically display APs when stimulated to contract

True

50

Explain "stress relaxation"

Slow stretch of single unit
Bladder stretches and holds urine without increasing pressure

51

Regulation of smooth muscle contraction occurs on ___
*skeletal?

Thick filaments
Myosin
*thin filament

52

Ca binds ___ and this complex binds ___, and this complex does what?

Calmodulin
MLCK
-phosphorylates a serine residue on 2 of the light chains

53

If MLCK is high___

Myosin is largely phosphorylated and has high ATPase activity
High Ca levels

54

Constant and stable low level of contraction.
Seen in what organs?

Tone
GI sphincters
blood vessels

55

True or false:
Smooth muscles shorten during the latch state.

False

56

Efficiency is ___ in smooth muscle
Economy is ___

Low
High

57

Low levels of ___ cause relaxation in smooth muscle

Phosphorylated myosin light chains

58

Ca is removed from the cell by ___

Sarcolemma 3 Na/Ca exchanger
Ca ATPase

59

Resting membrane potential of smooth muscle is

-55