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Physiology > Smooth muscle > Flashcards

Smooth muscle Flashcards

1
Q

Smooth muscle fibers are larger or smaller than skeletal muscle fibers?

A

Smaller (thinner and shorter)

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2
Q

Does smooth muscle contain striations?

A

No

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3
Q

True or false: all smooth muscle is largely the same

A

False- differs in innervation, packaging, organization

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4
Q

Where are nuclei found in smooth muscle?

A

Centrally

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5
Q

What are multi-unit smooth muscle?

A

discrete smooth muscle fibers that contract independently

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6
Q

What are unitary smooth muscle?

A

a group of fibers that contract together as a single unit

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7
Q

Which type of smooth muscle utilizes gap junctions?

A

Unitary smooth muscle

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8
Q

Which type of smooth muscle is utilized for small movements?

A

multiunit

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9
Q

Which type of smooth muscle are organized into sheets or bundles that contract together?

A

Unitary

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10
Q

Which type of smooth muscle utilizes the ANS primarily?

A

Multiunit

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11
Q

Which type of smooth muscle utilizes hormones?

A

Unitary

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12
Q

Do smooth muscles express troponin?

A

No

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13
Q

What is the difference in the myosin head in smooth muscle? What does this allow for?

A

that the myosin heads are not all arranged in the same direction. This allows for multi-directional contraction or force generation can in multiple in multiple planes.

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14
Q

What is the function of the dense bodies found dispersed throughout smooth muscle cells?

A

Like z discs

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15
Q

What replaces Z discs in smooth muscle?

A

Dense bodies

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16
Q

What is the function of the dense bodies?

A

Allow for force of contraction to be transmitted from one cell to the next

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17
Q

What is the arrangement of myosin in smooth muscle?

A

Arranged in multiple planes

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18
Q

Which attaches to the dense bodies: actin or myosin?

A

Actin

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19
Q

What is the primary source of Ca in smooth muscle?

A

the extracellular fluid

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20
Q

How much Ca does the sarcoplasm contribute to smooth muscle cell contraction

A

Very little

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21
Q

What is the point of regulation for Ca in smooth muscle? (What does Ca bind to? What enzyme is affected? What does this cause?)

A

Binds to calmodulin, and activates myosin light-chain kinase (MLCK). This then phosphorylates the regulatory chain of myosin ATPase

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22
Q

In skeletal muscle ATPse is always on. Is this the case for smooth muscle? How?

A

No, must be activated by myosin light chain kinase

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23
Q

What forms the cross bridge between myosin head and actin?

A

Phosphorylation by from ATP, from myosin phosphorylase

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24
Q

Decreased MLCK activation and myosin phosphatase activity can lead to what?

A

Relaxation or tonic contraction

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25
Q

When intracellular [Ca] falls, what happens?

A

Prevents further MLCK activation,

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26
Q

Where can multi-unit smooth muscle be found?

A

Ciliary and iris muscle of the eyes, piloerector muscles

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27
Q

What is the action of MLCK?

A

Phosphorylate the regulator chain of myosin ATPase

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28
Q

What state is the myosin head in (in smooth muscle) when ADP + Pi is bound to it?

A

Actin and myosin are bound

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29
Q

What happens when myosin loses the ADP +Pi?

A

Power stroke

30
Q

What is the chemical change in smooth muscle that allows myosin to detach?

A

ATP binds to the myosin head

31
Q

How many molecules of ATP are needed for smooth muscle contraction?

A

2–One ATP molecule is needed for the phosphorylation of the regulatory chain of myosin and the second ATP molecule is needed for the cross bridge cycling.

32
Q

What brings about relaxation of smooth muscle?

A

A decrease in [Ca], leading to a decrease in MLCK activation

33
Q

What is the primary innervation of multiunit smooth muscles?

34
Q

What is the primary innervation of unitary muscles?

A

Autonomics, as well as environmental factors

35
Q

Which type of smooth muscle cells have gap junctions, unitary or multiunit?

36
Q

Where are unitary muscles primarily found?

A

GI tract, bile ducts, ureters, uterus, blood vessels

37
Q

Is ATPase regulated in skeletal muscle? How about in smooth muscle? What is the regulator in each (if any)?

A

No regulation in smooth muscle

Calmodulin/Ca complex turn it on for smooth muscle

38
Q

How many inorganic phosphates are bound to myosin in skeletal muscle? Smooth muscle?

A

One is skeletal

Two in smooth

39
Q

What causes the power stroke in smooth muscle?

A

The loss of ADP and one of the Pi

40
Q

What recocks the myosin head in smooth muscle?

A

Binding of a new ATP

41
Q

What must happen to the ATP on the myosin head to allow for attachment of the head to actin?

A

must be hydrolyzed to ADP

42
Q

What are the two ways in which smooth muscles can relax?

A
  1. Lower [Ca]

2. Dephosphorylation of myosin by myosin phosphatase

43
Q

What are the two chemical changes that can lead to the “latch bridge” state?

A

Low MLCK and myosin phosphatase activity

Low ATPase activiy

44
Q

What is the chemical state of myosin in the latch state?

A

ADP and Pi can be bound, but the regulatory Pi is not.

45
Q

How many ATP molecules are needed for contraction in smooth muscle? What is the reason for this?

A

2-One ATP molecule is needed for the phosphorylation of the regulatory chain of myosin and the second ATP molecule is needed for the cross bridge cycling.

46
Q

Which type of muscle can have rapid contraction and relaxation? Opposite?

A

Skeletal

Opposite = smooth

47
Q

Which cross bridge cycling is fast: skeletal or smooth? Which is slow?

A 
Fast = Skeletal
Slow = Smooth
48
Q

What is the max force that skeletal muscle can generate?

A

3-4 kg/m^2

49
Q

What is the max force that smooth muscle can generate?

A

4-6 kg/m^2

50
Q

Which type of muscle is able to under a latch mechanism?

51
Q

Which type of muscle has stress-relaxation?

52
Q

Which muscle type exerts more energy for fast twitches? Slow?

A

Fast, smooth uses more

Slow, skeletal uses more

53
Q

Why can smooth muscle require less energy to produce the same tension over an extended period of time, when it require more ATP per cycle of myosin movement?

A

Far less cycles occur to maintain contracted state

54
Q

During smooth muscle relaxation, ATPase activity is relatively (large or small)? What is the consequence of this?

A

Small

The actin-myosin cross bridge is not formed

55
Q

There are no neuromuscular junctions in smooth muscle. How, then, is smooth muscle innervated?

A

Via diffuse branches of nerve fibers that lay over sheets of smooth muscle

56
Q

What accounts for the slow onset of an action potential activating a smooth muscle?

A

There is more physical space between the neuron varicosities compared to a neuromuscular plate

57
Q

What are the bodies along an axon terminal that innervate smooth muscles?

A

Varicosities

58
Q

What are the primary neurotransmitters in smooth muscle control? Which is usually excitatory, and which is usually inhibiting?

A

Norepi =inhibiting

Acetylcholine = excitatory

59
Q

True or false: when acetylcholine plays an excitatory role in smooth muscle innervation, norepi always plays the exact opposite, and vice versa

60
Q

“In some cases of (BLANK) smooth muscle, nerve fiber does contact the smooth muscle, forming a ‘contact junction’”.

61
Q

What is electro-mechanical stimulation? How could this occur?

A

a change in membrane permeability that results in a depolarization of smooth muscle. This could occur if membrane sodium or calcium channels were opened.

62
Q

What is electro-mechanical inhibition? How could this occur?

A

change in membrane permeability that results in a hyperpolarization of smooth muscle. This could occur if membrane sodium or calcium channels were closed or if potassium channels were opened.

63
Q

What is pharmacomechanical stimulation? How could it occur?

A

stimulation of smooth muscle contraction by signaling molecules. For example, some hormones will activate the phospholipase C (PLC) pathway through their respective receptor.

64
Q

What is pharmacomechanical inhibition? How could it occur?

A

as the inhibition of smooth muscle contraction mediated by signaling molecules. For example, some hormones will activate the protein kinase A (PKA) pathway, causing MLCK to be phosphorylated/deactivated

65
Q

What are the three different regulator categories of smooth muscle?

A

Neurotransmitters
Chemical/physical factors
Hormones

66
Q

What are the two roles of [Ca] in smooth muscle contraction?

A

Can cause action potential

Activates MLCK

67
Q

What are the two types of action potentials in smooth muscles?

A

Spike potentials

ACtion potentials ith plateaus

68
Q

What is the resting membrane potential of smooth muscles? How does this compare to skeletal?

A

around -60 mV. Lower (absolute value) compared to skeletal muscle (~-90 mV)

69
Q

What is responsible for the prolonged phase action potential (the pone with a plateau)?

A

Ca (channels are slower to open and close)

70
Q

What is the slow wave potential? What is the consequence of this?

A

a basoelectrical rhythm of membrane potential that occurs at rest.

This means that a smooth muscle cell is more likely to be depolarized at peaks in the baseoelectric rhythm

71
Q

What are the 9 hormones that affect smooth muscle function?

PO-HEAVENS

A 
Norepi
Epi
Angiotensin
Endothelin
Vasopressin
Oxytocin
Serotonin
Histamine
Prostaglandins

Physiology (75 decks)

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