9 - Smooth Muscle Flashcards Preview

Physiology Exam 1 > 9 - Smooth Muscle > Flashcards

Flashcards in 9 - Smooth Muscle Deck (73):
1

There are two types of smooth muscle. What are they?

1 - Multi-unit
2 - Unitary (syncytial or visceral)

2

What is multi-unit smooth muscle?

Discrete smooth muscle fibers that contract independently of each other

3

Where would you find multi-unit smooth muscle?

Ciliary and iris muscles of the eye as well as piloerector muscles

4

Do multi-unit smooth muscles communicate through gap junctions?

No - they do not communicate with each other

5

What are multi-unit smooth muscle fibers innervated by?

Autonomic nervous system

6

What is unitary smooth muscle?

A group of smooth muscle fibers that contract together as a single unit

7

How are unitary smooth muscle fibers usually arranged?

In sheets or bundles - these arrangements usually work together in concert

8

What are unitary smooth muscle fibers innervated by?

The Autonomic nervous system as well as non-neuronal regulators such as hormones or metabolites

9

Is each fiber of a unitary muscle innervated?

No - this is different from multi-unit smooth muscle.

Each bundle or sheet of unitary smooth muscle is innervated at specific points and the signal is then communicated between fibers via gap jucntions

10

What does this system of innervation and communication allow for?

Unitary smooth muscles are able to exhibit synchronized contractions for the entire group of fibers

11

Where would you find unitary smooth muscle fibers?

- GI tract
- Bile duct
- Ureters
- Uterus
- Blood vessels

12

What contractile elements will you find in smooth muscle?

Actin
Myosin
Tropomyosin

13

What are you missing in smooth muscle contraction that you utilize in skeletal muscle contraction?

Troponin

14

How is myosin different in smooth muscle than it is in skeletal muscle?

In smooth muscle, all the myosin heads are not arranged in the same direction

15

What does the irregular arrangement of myosin in smooth muscle allow for?

Multi-directional contraction or force generation in multiple planes

16

What are dense bodies similar to in skeletal muscle?

Dense bodies are functionally similar to Z discs of skeletal muscle

17

What do dense bodies consist of?

Structural proteins that are disbursed throughout the cell

18

What is the function of dense bodies?

THey serve to anchor adjacent cell to each other

19

What does the cellular connection via dense bodies allow for?

The force of contraction can be transmitted from one cell to the next

20

What else do dense bodies serve to do?

They are the anchoring point for actin thin filaments

21

Do actin and myosin have similar or different functions in smooth muscle and skeletal muscle?

Very similar

22

What does actin attach to in smooth muscle?

Dense bodies

23

Where do you find myosin in smooth muslce?

Interspersed between the actin filaments

24

During smooth muscle contraction, do actin and myosin undergo the same sliding overlap?

It is similar but it has a different contractile structure than skeletal muscle due to the arrangement of mysoin heads

25

What occurs structurally at the molecular level during smooth muscle contraction?

Due to the multidirectional arrangements of myosin heads and the arrangement of structural proteins in all planes of the cell, the contraction allows for SHRINKING and BULGING of the cell

26

How is the shrinking and bulging of the cell in smooth muscle different from the muscle contraction in skeletal muscle?

In skeletal muscle, the muscle fiber simply shortens in length rather than getting pulled in multiple directions

27

How is the regulation of myosin different in smooth muscle than it is in skeletal muscle?

The source of calcium is different

28

What is the primary source of Ca++ in skeletal muscle?

Sarcoplasmic reticulum

29

What is the primary source of Ca++ in smooth muscle?

The extracellular fluid

30

What accounts for this difference?

The sarcoplasmic reticulum in smooth muscle is not well developed and is a weak source of calcium

31

What does the Ca++ of smooth muscles do once it enters the cell?

Binds to a protein called calmodulin

32

What does the calcium-calmodulin complex activate?

Myosin light-chain kinase (MLCK)

33

What does the MLCK enzyme do?

Phosphorylates the regulatory chain of myosin - this ultimately regulates the activity of the myosin ATPase

34

Is the attachment and detachment cycle of myosin and actin using ATP similar or different to the cycle seen with skeletal muscle?

Similar

35

What does a decrease of calcium lead to?

Dephosphorylation of the regulatory domain of myosin

36

What happens when the regulatory domain of myosin is not phosphorylated?

Relaxation

37

What is the latch state?

A state that forms which allows persistent contraction with low energy requirements

38

What occurs that allows the latch state to be maintained

Once the actin-myosin bridge forms, the regulatory site can be dephosphorylated

There is reduced ATPase activity and therefore a "slow" power stroke

This causes the actin-myosin bridge to be maintained for a relatively long period of time in a tonic contraction

39

Are neuromuscular junctions found in smooth muscle like they are in skeletal muscle?

No

40

Instead of neuromuscular junctions, what type of innervation do we see from neurons?

DIffuse branches of nerve fibers that lay over sheets of smooth muscle

41

Is there an end foot at the end of a nerve terminal in smooth muscle?

No - instead there are varicosities, which release neurotransmitters

42

What types of neurotransmitters regulate smooth muscle contraction?

Norepinephrine
Acetylcholine

43

What chemicals regulate smooth muscle contraction?

Metabolic products, ions, gases

44

What hormones regulate smooth muscle contraction?

Endothelin
Angiotensin
Vasopressin

45

What is electromechanical stimulation?

A change in membrane permeability that results in a depolarization of smooth muscle

46

When would electromechanical stimulation occur?

If sodium or calcium channels were opened

47

What is electromechanical inhibition?

A change in membrane permeatiblity that results in the hyperpolarization of smooth muscle

48

When would electromechanical inhibition occur?

If membrane sodium or calcium channels were closed or if potassium channels were opened

49

What is pharmacomechanical stimualtion?

The stimulation of smooth muscle contraction by signaling molecules

50

When would pharmacomechanical stimulation occur?

Some hormones will activate the phospholipase C (PLC) pathway through their receptor, which then increases the intracellular concentration of the second messenger (IP3) which then allows intracellular stores of calcium to be released and smooth muscle to contract

51

What is pharmacomechanical inhibition?

The inhibition of smooth muscle contraction which is mediated by signaling molecules

52

When would pharmacomechanical inhibition occur?

Some hormones will activate the Protein Kinase A (PKA) pathway, which then phosphorylates MLCK, whcih prevents the calcium-calmodulin complex from activating MLCK, which blocks muscle contraction

Some hormones activate myosin phosphatase, which leads to an inhibition of the contractile process as well

53

How does calcium participate in electrical events in smooth muscles?

Depolarization due to movement of Ca++ into the cell

54

How does calcium participate in mechanical events in smooth muscle?

Calcium inside the cell binds to calmodulin, which is required to activate MLCK and contract the muscle

55

What is a spike potential of smooth muscle?

A type of smooth muscle action potential that resembles a normal action potential

56

What causes the depolarization (incline) of a spike potential?

Depolarization due to Ca++ and Na+ movement into the cell

57

What causes the hyperpolarization (decline) of a spike potential?

Repolarization due to K+ movement out of the cell

58

What is an action potential with a plateau in smooth muscle?

A type of smooth muscle action potential that depolarizes until it reaches its peak, begins to hyperpolarize and decline, but experiences a prolonged plateau before eventually completing the hyperpolarization back to resting potential

59

What causes the plateau in an action potential in smooth muscle?

Prolonged and slow opening of Ca++ channels

60

What is a resting slow wave of a smooth muscle membrane?

A continuous cycling of depolarization and repolarization without eliciting a spike potential that would lead to a contraction

61

Is the membrane of a resting slow wave ever at rest?

No - it continues to depolarize and repolarize

62

What occurs at the peak of depolarization of a slow wave?

Rapid depolarization or a spike potential can occur at this peak of depolarization - this can lead to contraction

63

Where would you find smooth muscle that exhibits a resting slow wave?

Smooth muscle of the gastrointestinal tract

64

What type of smooth muscle contains cells that are connected via gap junctions?

Unitary smooth muscle

65

What type of smooth muscle would you find in the small intestine?

Unitary smooth muscle

66

What is a contractile protein that is present in skeletal muscle but not smooth muscle?

Troponin

67

What protein can bind to calcium in smooth muscle?

Calmodulin

68

What protein can bind to calcium in skeletal muscle?

Troponin

69

Which type of regulator will stimulate smooth muscle contraction, acetylcholine or epinephrine?

CAN'T TELL - it is tissue specific

70

What is the primary source of calcium for smooth muscle contraction?

Extracellular fluid

71

What does the calcium from the extracellular fluid allow for?

Change in membrane potential and a contractile event

72

What ions are responsible for the depolarization of smooth muscle?

Sodium and calcium

73

True or false: a change in membrane potential is required to induce smooth muscle contraction

No - it CAN, but it is not required