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Physiology > Smooth Muscle > Flashcards

Smooth Muscle Flashcards

1
Q

What are general properties of smooth muscle?

A
  • Located on hollow organs and not attached to skeleton
  • capable of sustained contractions with minimum energy use
  • innervated by autonomic nervous system (extrinsic innervation) and by neurons in plexuses with smooth tissue (intrinsic innervation) especially in the GI tract
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2
Q

What innervates extrinsic innervation?

A

autonomic nervous system

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3
Q

What innervates intrinsic innervation

A

neurons in plexuses with smooth muscle tissue (eg. GI tract)

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4
Q

What is the histology of smooth muscle fibers?

A
  • uninucleate
  • spindle shaped
  • smaller than skeletal muscle fibers
  • SR is not as elaborate as skeletal muscle
  • No T-tubules, but has rows of caveolae
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5
Q

What are properties of the caveolae rows in smooth muscle fibers?

A
  • increased surface-to volume ratio
  • lay close to SR
  • contains voltage gated Ca channels and other proteins probably involved in many forms of signal transduction
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6
Q

What are the types of smooth muscle?

A

Single-unit (visceral) and Multiunit

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7
Q

Where are single-unit smooth muscles found?

A

Intestines, uterus, small arteries and veins

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8
Q

What connects single unit cells? What’s their function?

A

Gap junctions that allow for response as a unit

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9
Q

Do single-unit or multiunit smooth muscles have spontaneous fluctuations in the membrane potential?

A

Single unit

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10
Q

Which type of smooth muscle, single-unit or multi unit, has no action potentials?

A

multiunit

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11
Q

Where can you find multiunit smooth muscle?

A

Iris and ciliary muscles

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12
Q

What defines a multiunit smooth muscle?

A

few gap junctions and individual cells that respond independently, allowing for finer control

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13
Q

In the smooth muscle contractile mechanism, what are the involved contractile proteins? How does it differ than skeletal muscle?

A

myosin, actin, and tropmyosin

NO TROPONIN

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14
Q

What is the structure of smooth muscle contractile proteins? How do they differ than skeletal muscle?

A

Thin filaments anchor to Dense bodies (not z-line). Each group of thin filaments surrounds a few thick ones. Lots of thin filaments to thick filaments.

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15
Q

What is the biochemistry of activation, contraction and relaxation of smooth muscle?

A
  1. Stimulation leads to increased [Ca2+]_i
  2. Calcium binds to calmodulin
  3. Ca-calmodulin complex activates myosin light chain kinase (MLCK)
  4. MLCK phosphoylates the light changes of myosin molecules
  5. Phosphoylated myosin interacts with actin producing a contraction
  6. Ca2+ is actively pumped out of the cell or into the SR causing a fall in [Ca2+]_i
  7. MLCK inactivates; phosphoylation of myosin stops
  8. MLC phosphatase dephosphoylates the myosin light kinase chains
  9. Smooth muscle relaxes

In summary, smooth muscle force is a balance between phosphoylation and dephosphoylation of the myosin light chain

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16
Q

True or False: the contractile at any given Ca2+ level can be modulated by altering the activity of kinase or phosphatase

A

TRUE! SO TRUE!

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17
Q

What is a Beta_2-receptor activation do? Where does it occur?

A

increases cAMP levels, which activates protein kinase A, which phosphorylates MLCK. Results in less tension being produced due to less activity from MLCK.

Occurs on vascular or bronchiolar smooth muscle

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18
Q

What is the affect of Nitric oxide (NO) on the contractile force?

A

NO increases intracellular cGMP leels, which activates protein kinase G, which phosphoylates the myosin light chain kinase (MLCK). Therefore, less tension is produced.

19
Q

What is the effect of excitatory stimuli on the contractile force?

A

Some excitatory stimuli activate phospholipase C, which produces IP_3 and diacylglycerol (DAG).

phosphoylation reduces the activity of MLC phosphatase resulting in a greater tension

20
Q

What to actions would alter the activity of either kinase or phosphotase to produce less tension?

A

introduction of nitric oxide or beta_2-receptor activation

21
Q

What to actions would alter the activity of either kinase or phosphotase to produce more tension?

A

introduction of excitation stimuli to produce IP_3 or diacylglycerol (DAG)

22
Q

What are the three general ways of regulating intracellular Ca2+?

A

Ca2+ influx across the sarcolemma
Ca2+ efflux from SR
Extrusion of Ca2+ from myoplasm

23
Q

What channels regulate Ca2+ influx across the sarcolemma?

A
  • voltage gated Ca channels
  • receptor-regulated Ca channels
  • store operated Ca channels
24
Q

What opens receptor-regulated Ca channels? Do they produce a depolarization?

A

neurotransmitter or hormones.

Little or no depolarization is generated.

25
Q

What opens store-operated Ca channels? what is it’s function?

A

low SR Ca levels.

function: replenish SR Ca

26
Q

What are two ways to produce Ca2+ efflux from the SR?

A

Via receptor-regulated efflux or

Ca2-induced Ca2+release from the SR

27
Q

What is the mechanism behind receptor -regulated efflux of Ca2+ from the SR? What type of membrane is created?

A

the binding of a neurotransmitter or hormone to the receptor causes formation of a second messenger (IP_3) which causes release of Ca2+ from the SR.

No membrane potential change occurs.

28
Q

What is the mechanism between Ca2+-induced Ca2+ release from SR

A

Ca2+ influx across the sarcolemma release Ca2+ from the sarcoplasmic reticulum.

29
Q

Which of the two ways to produce Ca2+ efflux is more important?

A

IP_3-induced release

30
Q

Whare are two pathways of extruding Ca2+ from the myoplasm?

A

via sarcolemma pathway and SR pathway

31
Q

What two amazing molecules help you extrude Ca2+ from the myoplasm via the sarcolemma pathway?

A
  1. Ca pump (PMCA)

2. Na-Ca exchanger

32
Q

What does the Ca pump (PMCA) do?

A

extrude Ca2_ from tye myopalsm via the sarcolemma

33
Q

What does the Na-Ca exchanger do?

A

Move Calcium out of from the myoplasm via the sarcolemma for Sodium in.

34
Q

What is the way via the sarcoplasmic reticulum pathway to extrude Ca2+ from the myoplasm?

A

First use Ca pumps on SR membrane (CERCA)

then use SR Ca2+ binding proteins

35
Q

What does SERCA do?

A

pump Ca2+ ointo the SR

36
Q

What does calrecticulin do?

A

it’s a protein that binds Ca2+ to remove it from the SR

37
Q

what does calsequestrin do?

A

binds Ca in the SR

38
Q

Describe the speed of contraction and energy supply in smooth muscle.

A

Contraction relaxation cycle is very slow in smooth muscle (seconds). Crossbridge recyling in smooth muscle require ATP, but the sustained contraction in smooth muscle consumes much less ATP than skeletal muscle

39
Q

Why is the contraction relaxation cycle so slow in smooth muscles?

A

myosin has very slow attachment and detachment rates AND pumping of Ca2+ out of the myoplasm is slow

40
Q

Describe properties of crossbridge recycling in smooth muscle

A
  1. Requires ATP
  2. no creatine phosphate reserve
  3. most of ATP comes from aerobic metabolism, but ATP can be produced anaerobically when oxygen is low
41
Q

What effect does slow myosin attachment and detachment rate have on the amount of ATP use in a sustained contraction?

A

Much less ATP used in a sustained contraction than skeletal muscle

42
Q

How does the length-tension relationship and degree of shortening in smooth muscles compare to skeletal muscles?

A

Smooth muscles generate tension under GREATER STRETCH (increased lengths) and GREATER DEGREE OF SHORTENING (decreased lengths) than skeletal muscle

43
Q

What is smooth muscle tone?

A

a sustained level of tension in a smooth muscle resulting from free Ca2+

Physiology (9 decks)

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