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2023 Systems Phys > Smooth Muscle > Flashcards

Smooth Muscle Flashcards

1
Q

Where is smooth muscle located?

A

in the walls of holloow organs (gallbladder, uterus, bladder)
Tubes (GI tract, blood vessels)

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2
Q

What is a major purpose of smooth muscle?

A

maintain organ shape and push contents along

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3
Q

Describe smooth muscle contraction

A

slower and longer than skeletal muscle
more efficient
responds to variety of stimuli
latch state possible

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4
Q

Why is smooth muscle contraction more efficient than skeletal muscle contraction?

A

Generates comparable force using 300X less ATP
gives up speed for ability to adapt and adjust

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5
Q

What does the latch state do?

A

provides prolonged contraction w/o input of ATP

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6
Q

What is the structure of smooth muscle?

A

dense bodies (instead of z lines)
tropomyosin
caveolae (instead of t tubules)
underdeveloped SR

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7
Q

What do dense bodies do?

A

anchor actin

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8
Q

What holds dense bodies in place?

A

intermediate filaments

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9
Q

What does smooth muscle lack that skeletal muscle has?

A

sarcomeres (no striations)
troponin
t-tubules

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10
Q

Why is the SR not well developed in smooth muscle?

A

intracellular Ca2+ is less important

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11
Q

How is actin/myosin arranged in smooth muscle?

A

oriented diagonally
diamond-shaped lattice (not parallel with long axis)

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12
Q

What does sliding cause in smooth muscle?

A

causes cells to shorten and expand

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13
Q

What do long thin filaments allow in smooth muscle?

A

a large range of shortening (to fully expel bladder)

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14
Q

What are the two types of smooth muscle?

A

Single Unit
Multiunit

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15
Q

Define: Single Unit Smooth Muscle

A

only a few muscle fibers innervated in each group
stimulatd together, contract together

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16
Q

Single Unit smooth muscle can be stimulated by…

A

innervation, stretch, and hormonally

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17
Q

Explain Single Unit smooth muscle

A

Few muscles innervated in each group
impulse spreads through gap junctions
whole sheet contracts as unit
stimulated together, contract together

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18
Q

What is the structure of neuromuscular synapse in smooth muscle?

A

neurons have multiple varicosities (swellings of axons)
No complex structure at synapse (no MEP)
one smooth muscle can get input from both PNS and SNS

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19
Q

What do pacemaker cells do in single unit smooth muscle?

A

initiate spontanoeous electrical activity that spreads throughout the muscle

20
Q

What are the two types of fluctuations in electrical activity in single unit smooth muscle?

A

Slow Wave Potentials
Action (spike) Potentials

21
Q

Define: Slow Wave Potentials

A

coordinate muscle contractions in the gut by controlling the appearance of a second type of depolarizing event

22
Q

Where do action potentials occur in single unit smooth muscle?

A

only occur at the crests of slow waves

23
Q

Excitation-Contraction Coupling in smooth muscle

A

RMP is relatively low (-50 to -60 mV)
Long AP = 10-50 ms
No voltage gated Na+ channels at “motor end plate”
Voltage gated Ca2+ channels (dihydropyridine)

24
Q

What is the dihydropyridine receptor in skeletal muscle?

A

voltage sensor

25
Q

What is the dihydropyridine receptor in cardiac muscle?

A

voltage-dependent Ca2+ channel
only lets a little Ca2+ in

26
Q

What is the dihydropyridine receptor in smooth muscle?

A

voltage-dependent Ca2+ channel lets in enough Ca2+ for AP

27
Q

What does Ca2+ effect in smooth muscles?

A

the state of thick filaments

28
Q

Where does Ca2+ come from in smooth muscles?

A

Mostly outside the cell, a little is released by the SR

29
Q

How does Ca2+ enter the smooth muscle cells from the outside?

A

Depolarization -> voltage-gated Ca2+ channels open
NTs, hormones, etc. open Ca2+ channels

30
Q

Smooth muscle contraction

A

Extracellular Ca2+ enters cell
Ca2+ binds calmodulin
activates myosin light chain kinase (MLCK)
MLCK phosphoylates light chain of myosin
phosphorylated myosin allows crossbridges to form and break repeatedly

31
Q

In smooth muscle, myosin is….

A

“off”

32
Q

In skeletal muscle, myosin is….

A

always “on”

33
Q

Smooth muscle relaxation mechanism

A

Contractile stimulus is removed -> Ca2+ concentration decreases
or direct actionh of a substiture that inhibits the contractile mechanis, (increase myosin phosphatase activity)

34
Q

Pharmacological Relaxation of smooth muscle

A

L-type Ca2+ channel blocker
increase in cAMP or cGMP

35
Q

What does cAMP do in smooth muscle?

A

(EPI via β2) inhibits MLCK

36
Q

What does cGMP do in smooth muscles?

A

(nitroglycerin) stimulates myosin phosphatase

37
Q

What is EPI used or in relation to smooth muscle?

A

used in treatment of bronchospasm of asthma

38
Q

What is nitroglycerin used for in terms of smooth muscles?

A

used to relax cornary arteries
converted to nitric oxide in the body

39
Q

What is Sildenafil used for?

A

cGMP phophodiesterases for ED

40
Q

Sexual stimulation -> production and release of __ -> activates __ -> prodices __-> results in __-> increase in BF

A

NO
guanylate cyclase
cGMP
smooth muscle relaxation

41
Q

How can vascular smooth muscle (aorta) endure 60 “insults” per minute and sustain BP w/o expending a lot of ATP?

A

Develop force
smooth muscle has a way for cross bridges to remain attached, cycle slowly, and consume less ATP
partial constriction
Latch State

42
Q

Mechanism of Tonic Contraction

A

Dephosphorylation of myosin while still attached to actin -> ATPases activity decreases -> more difficult to release myosin heads from actin; slow cross-bride cycling (low ATP use)

43
Q

What does the mechanism of tonic contraction result in?

A

more difficult to release myosin heads from actin; slow cross-bride cycling (low ATP use)

44
Q

Increased intracellular Ca2+ in smooth muscle…

A

regulates myosin

45
Q

Ca2+ is increased in smooth muscle through:

A

Mechanically gated Ca2+ channels
Ligand gated Ca2+ channels (ANS, hormones, paracrine)
Voltage gated Ca2+ channels

46
Q

Smooth muscle is capable of which types of contraction?

A

phasic (short term) and tonic

47
Q

Overlapping myofilaments in smooth muscle

A

slide and generate force

2023 Systems Phys (41 decks)

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