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BIOL1011 > Smooth muscle > Flashcards

Smooth muscle Flashcards

1
Q

Why is smooth muscle called what it is?

A

it does not give the histological appearance of cross-striations

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2
Q

Is smooth muscle under voluntary or involuntary control? What controls its functions?

A

It is involuntary meaning it is under autonomic and hormonal control

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3
Q

What is smooth muscle specialised for?

How does this compare with skeletal muscle?

A

Smooth muscle is specialised for continuous contractions of relatively low force, under involuntary control

Whereas, Skeletal muscle is specialised for relatively forceful contractions of short durations and under fine voluntary control

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4
Q

Where is smooth muscle found?

A

It is present in the walls of hollow organs like the urinary, bladder, uterus, stomach and intestines

Also present in passageways, such as the arteries, and veins of circulatory system

And tracts of respiratory, urinary and reproductive systems

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5
Q

how many nuclei does a smooth muscle cell have and where is that nucleus located?

A

they have one nuclei per cell and it is located right in the middle of the cell

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6
Q

What is the shape of the cell’s described as?

A

Spindle shaped cells.

This means that they are wider in the middle than at the ends

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7
Q

What’s not present in smooth muscles?

A

T tubules

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8
Q

What’s on the outside/inside of the cell:

Circular smooth muscle

longitudinal smooth muscle

A

Longitudinal is found on the inside

circular is found on the outside

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9
Q

What are the 2 forms of smooth muscle?

A

circular smooth muscle

and

longitudinal smooth muscle

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10
Q

label this electronmicrograph of smooth muscle?

A
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11
Q

What do dense bodies contains and what’s their main function?

A

dense bodies contain lots of proteins and they help anchor filaments

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12
Q

What do smooth muscle produce and what is this called?

A

smooth muscle produces its own connective tissue, known as endomysium

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13
Q

What structures do smooth muscles not contain?

What structures do they have?

A

Don’t contain: striations, sarcomeres, T tubules

Do contains: actin, myosin, thin/thick filaments

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14
Q

What are Ca2+ ions supplied by ?

(2 regions)

A

They are supplied by the SR in the fibres

and

by sequestration from the extracellular fluid through membrane indentations called Calveoli

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15
Q

When the muscle contracts, does the distance between dense bodies becomes shorter or longer?

A

shorter

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16
Q

Label this relaxed/ contracted smooth muscle

A
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17
Q

What does the skeletal muscle act against?

What does smooth muscle act against?

A

Skeletal muscle acts against the skeleton

Smooth muscle acts against the extracellular matrix

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18
Q

The extracellular matrix that the smooth muscle acts against, secretes what?

A

collagen and glycoproteins

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19
Q

In smooth muscle, what is the tension generated by?

what is this tension transmitted through?

What overall effect does it cause?

A

The tension is generated by contraction and its transmitted through the focal adhesion densities to the surrounding connective tissue this allowing groups of cells to act as one

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20
Q

what does smooth muscle contraction depend on?

How is this mechanism different to skeletal muscle?

A

It is a Ca2+ dependant mechanism but smooth muscles does not contain troponin like skeletal muscle does

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21
Q

What are the steps to smooth muscle contraction?

A
  1. Ca2+ ions are released from caveolae/ SR
  2. Ca2+ ions form complex with calmodulin
  3. Ca2+ - calmodulin complex activates the myosin light chain kinase (MLCK)
  4. MLCK is phosphorylated and activates myosin ATPase activity
  5. myosin is now able to bind to actin
  6. ATP-dependant contraction cycle ensues
  7. contraction continues as long as myosin is phosphorylated
  8. Phosphatase cleaves the phosphate group
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22
Q

How is smooth muscle contraction stopped?

A

ATP-dependant calcium pumps actively transporting Ca2+ back into the SR and out of the cell

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23
Q

What is calmodulin sometimes referred to as?

A

CaM

OR

Calcium- modulated protein

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24
Q

What is CaM?

A

an intracellular target of the second messenger Ca2+

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25
Q

Once CaM is bound to Ca2+ what happens?

A

the CaM acts as part of a calcium signal transduction pathway by interacting with kinases and phosphatases

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26
Q

What is CaM structurally similar to?

A

Troponin

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27
Q

What remains in the cytoplasm after contraction and why? Why is it important?

A

A low concentration of Ca2+. This helps to maintain muscle tone. This is important in certain tracts and around blood vessles

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28
Q

Most smooth muscle’s must function for long periods of time without rest. What does this mean for their power output and the amount of energy they use?

A

They have a low power output and the contractions can continue without using large amounts of energy

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29
Q

Can some smooth muscle maintains contractions even as Ca2+ is removed and myosin kinase in inactivated (dephosphorylated)?

A

yes

30
Q

How does the contraction of smooth muscles occur without the presence of Ca2+?

Whats not needed?

What does this allow to maintain?

A

Cross-bridges can form between myosin heads and actin, these are known as latch-bridges. This helps keep the thick and thin filaments linked together for long periods of time without the need for ATP

This allows the maintaining of muscle ‘tone’ in smooth muscle that lines arterioles and other visceral organs

31
Q

Name some things that can stimulate smooth muscle?

A
  • Involuntary and contracts without nerve stimulation
  • hormones
  • stretch
  • metabolic state- CO2, low PH, O2 deficiency
  • autonomic nerve fibres stimulate multiple myocytes
32
Q

What influences the contractile activity of smooth muscle?

A

neurotransmitters which are released by autonomic neuron endings

33
Q

what do smooth muscles have instead of an end-plate region like the skeletal muscle’s have?

A

swollen regions known as varicosities

34
Q

What do varicosities contain?

How are these released from the varicosities?

A

many vesicles filled with neurotransmitters, some of which are released when an AP passes the varicosity

35
Q

What do varicosities form?

A

A single axon which is located along several muscle cells

36
Q

What are a number of smooth muscle cells influcenced by?

What is a single smooth muscle cell influenced by?

A

NUMBER of smooth muscle cells are influenced by the neurotransmitters released by a single neuron

ONE smooth muscle cell is influenced by neurotransmitters from more than one neuron

37
Q

What are the 2 types of units of smooth muscle cells?

A

single-unit smooth muscles

and

multi-unit smooth muscle

38
Q

What unit is more common in smooth muscles?

A

single unit is more common

39
Q

What is a single-unit smooth muscle?

A

The smooth muscle has its muscle fibres joined by gap junctions so that the muscle contracts as a single unit (the electrical signal is transferred across the gap junctions)

40
Q

Where is single-unit smooth muscle found?

What is it commonly called?

A

in the walls of all visceral organs (EXCEPT THE HEART)

so is commonly called the Visceral muscle

41
Q

What response does visceral muscle have?

What does this mean?

A

stress-relaxation response

This means that as the muscle of a hollow organs is stretched when it fills, the mechanical stress of the stretching will trigger contraction.

This is immediatly followed by relaxation so that the organ does not empty its comtents prematurely

42
Q

What does visceral muscle help maintain around the hollow organs?

A

muscle tone when the organ empties and shrinks, this prevents ‘flabbiness’ in the empty organ

43
Q

What type of contraction does visceral organ produce?

What does this allow?

A

A slow and steady contraction that allow substances, such as food in the digestive tract, to move through the body

44
Q

Why are multi-unit smooth muscle not electrically coupled?

A

They rarely possess gap junctions

45
Q

When a multi-unit is stimulated where does the impulse travel to?

A

The impulse doesn’t spread from one cell to the next but instead is confined to the cell that was originally stimulated

46
Q

Where does stimuli for the multi-unit smooth muscle come from?

A

the autonomic nerves or hormones but NOT from stretching

47
Q

Where is multi-unit smooth muscle found?

A

around large blood vessels, in the respiratory airways and in the eyes

48
Q

The fight or flight response leads to many physiological responses, it also causes chnages in smooth muscle activity. What type of changes does it cause?

A
  • skin- smooth muscle in follicles can cause hair to stand on end
  • eye- iris in smooth muscle dilates
  • stomach, intestines and bladder
  • bronchodilation
49
Q

What do gap junctions allow in single-unit smooth muscle?

How is this different in multi-unit smooth muscle?

A

Gap junctions in single-unit smooth muscle allow the spread of the electrical activity between all cells so they all contract as a single unit

Whereas, in multi-unit smooth muscle there is electrical isolation so when an impulse arrives only a few cells will contract as opposed to all

50
Q

Label the bronchiole?

A
51
Q

Label the layers of this electron microscrope image of a bronchiole

A
52
Q

Give an example of a therapeutic targeting of smooth muscle?

A

Beta2 agonist. It is found in salbutamol inhalers.

it targets Beta2 receptors (GPCR) located in bronchial smooth muscle, results in bronchodilation

53
Q

Tell me the steps to how the Beta2 receptor agonsit causes bronchodilation

A
54
Q

What coordinates the peristalic movement of the food bolus through the GI tract?

A

the longitudinal cross-sectional smooth muscles

55
Q

what decreases peristalisis?

A

the fight and flight response

56
Q

Whats the oesophagus?

A

A strong muscular tube that convery food from the oropharynx (part of the mouth) to the stomach

57
Q

is swallowing volunatary or involuntary?

A

voluntary

58
Q

whats an example of skeletal and smooth muscle working together?

A

swallowing

59
Q

in the oesophagus, is the circular or longitudinal smooth muscle found on the inside/outside?

A

circular smooth muscle on inside

longitudinal smooth muscle on outside

60
Q

what is the ureter made of?

A

smooth muscle fibres

61
Q

What process squeezes urine into the bladder?

A

peristalsis

62
Q

What are the layers of smooth muscle of the bladder?

A

inner longitudinal

middle circular

outer longitudinal

63
Q

label the ureter?

A
64
Q

whats the myometrium?

A

the smooth muscle tissue of the uterus

65
Q

during pregnancy how does the myometrium change?

A

it greatly increases in size?

66
Q

what does the hormone oxytocin stimulate?

A

the contraction of myometrium. helps to expel the foetus from the uterus

67
Q

Whats intravenous salbutamol been used for?

A

to relax the uterine smooth muscle to delay poremature labour-same mechanism as for bronchodilation

68
Q

when oxytocin binds to a receptor, what does it trigger the release of? How does this then result in contraction?

A

it causes the release of Ca2+ from the SR.

The Ca2+ ions bind to calmodulin which activates myosin light chain kinase (MLCK) which then results in contraction

69
Q

Tell me the differences between smooth muscle and skeletal muscle excitation and the steps that lead to an external force being generated?

A
70
Q

Tell me the stages to cross-bridge activation in smooth and skeletal muscle

A
71
Q

because smooth muscle cells do not contain troponin, cross-bridge formation is not regulated by the troponin-tropomyosin complex but is instead regulated by what?

A

the regulatory proteins calmodulin

BIOL1011 (8 decks)

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