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Physiology > Smooth Muscle > Flashcards

Smooth Muscle Flashcards

1
Q

Smooth muscle is under _____ control

A

involuntary

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2
Q

Smooth muscle are nonstriated b/c…

A

actin and myosin aren’t arranged in regular sarcomeres

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3
Q

Smooth muscle responds to what types of stimuli?

A
  • electrical signal

- hormones

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4
Q

Contraction of smooth muscle leads to…

A

alteration in dimension of organ

  • propels substance w/in organ
  • increase resistance to flow of substance
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5
Q

T/F: smooth muscles are more variable than skeletal muscles

A

T, b/c they operate over a wide range of lengths

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6
Q

Smooth muscles are arranged in…

A
  • circular
  • longitudinal
  • oblique
  • bundles
  • sheets
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7
Q

Differences between smooth and skeletal muscles:

A
  • contract and relax slower
  • lose less E
  • have less localized receptor sites
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8
Q

Smooth muscle is different based on…

A
  • location
  • contractions
  • arrangements
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9
Q

Visceral muscle:

A

lines walls of hollow internal organs

- organs part of gastrointestinal, urinary, respiratory, and reproductive systems

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10
Q

Vascular muscles are located in…

A

blood vessels

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11
Q

Types of smooth muscle that differ in location:

A
  • visceral
  • vascular
  • ocular
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12
Q

Types of smooth muscle that differ in contractions:

A
  • phasic

- tonic

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13
Q

Phasic contractions depend on…

A

the demands of the situation

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14
Q

Tonic contractions:

A

change diameters slowly

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15
Q

Tonic contractions can be…

A

maintained for long periods without fatigue

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16
Q

Tonic contractions use high/low ATP due to…

A

low, latch-bridge state

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17
Q

Smooth muscle cross-bridges cycle at…

A

slower rate than skeletal muscle

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18
Q

Different types of arrangements:

A
  • multiunit

- unitary

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19
Q

Multiunit arrangement:

A

individual cells and small groups of cells

- not electrically coupled

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20
Q

Multiunits act as…

A

many separate units b/c fibers operate independently

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21
Q

Multiunits are densely innervated by…

A

ANS fibers

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22
Q

Lots of nerves provide…

A

separate signals, which allows for greater control

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23
Q

Examples of multiunit smooth muscles:

A
  • very small blood vessels
  • muscles of skin
  • iris
  • ciliary body of eye
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24
Q

Unitary (single unit):

A

large # of cells that function together as a single unit

  • not as strictly controlled by ANS
  • electronically coupled
  • can be initiated by pacemaker cell
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25
Q

Unitary arrangements make up the bulk of…

A

visceral organs

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26
Q

Unitary arrangements control…

A

peristalsis (aka wave contraction)

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27
Q

Single unit and multiunits are both mostly…

A

combination of cell-cell coupling and locally produced activators/inhibitors

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28
Q

Innervations of smooth muscle are under…

A

involuntary NS control

- doesn’t need NS innervation

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29
Q

Smooth muscles are innervated by…

A

motor neurons of ANS

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30
Q

Motor neurons of ANS:

A
  • have no motor end plate
  • supply smooth muscle flow across tissue
  • NT released at varicosities
  • has electromechanical coupling like skeletal muscles
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31
Q

T/F: smooth muscles can also contract without innervation

A

T

- many have intrinsic activity

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32
Q

If smooth muscles can contract without innervation, what are the influenced by then?

A
  • hormonal factors

- environmental factors

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33
Q

Examples of hormonal factors:

A
  • uterine muscle response to oxytocin

- vasoactive substances (paracrine)

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34
Q

Environmental factors:

A
  • under myogenic control
  • contract when stretched
  • ex: distention of stomach
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35
Q

Smooth muscles that can contract without innervation acts via…

A

pharmacomechanical coupling

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36
Q

Smooth muscle cells are generally arranged in what kind of layers:

A
  • circular
  • longitudinal
  • helical (oblique)
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37
Q

T/F: smooth muscle cells are in antagonistic pairs

A

F

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38
Q

Smooth muscle cells around large blood vessels are arranged in…

A

helical/circular layers

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39
Q

Smooth muscle cells in arterioles are arranged in…

A

singular circular shape

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40
Q

When circular muscle is contracted…

A
  • diameter is decreased

- stops movement

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41
Q

When longitudinal muscle is contracted…

A
  • organ is shortened

- moves substance through

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42
Q

Varicosities:

A
  • periodical swellings of ANS neurons
  • has vesicles w/ NT
  • affected cells will depolarize
  • whole sheets contract as functional syncytium
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43
Q

APs in varicosities have…

A

long durations

- spread to neighboring cells via gap junctions

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44
Q

Smooth muscle cells don’t have:

A
  • fast VGC Na+
  • T-tubules
  • troponin
  • visible striated sarcomeres
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45
Q

Smooth muscle cells have:

A
  • slow L type VGC Ca2+
  • caveolae
  • calmodulin as regulatory protein
  • actin and myosin wrapped in spirals between dense bodies
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46
Q

T/F: smooth muscle is not myosin driven

A

F

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47
Q

Single units are connected by…

A

gap junctions

  • forms low-resistance pathway
  • allows for electrical and chemical communication
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48
Q

Single units are…

A
  • small
  • mononucleated
  • spindle shaped
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49
Q

Dense bodies in single units act as…

A

z line because it connects actin and myosin bundles

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50
Q

T/F: there are the same amount of actin in skeletal muscle as smooth muscle

A

F, there are x2 the amount of actin in smooth muscle

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51
Q

Actin:

A
  • has no troponin, so not bound to tropomyosin

- myosin binding site is exposed

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52
Q

Myosin:

A
  • not in ready state
  • not cocked
  • 1/4 of the amount in skeletal muscle
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53
Q

Myosin has myosin linked regulatory proteins, which are:

A
  • myosin light chain (MLC)
  • myosin light chain kinase (MLCK)
  • myosin light chain phosphatase (MLCP)
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54
Q

Myosin light chain (MLC) is at the…

A

base of myosin head

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55
Q

Function of myosin light chain kinase (MLCK):

A

phosphorylates MLC, which will activate myosin ATPase

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56
Q

Function of myosin light chain phosphatase (MLCP):

A

dephosphorylates MLC, which decreases myosin ATPase activity

57
Q

Ratio of MLCK and MLCP determine…

A

the ability of smooth muscles to respond to Ca2+

58
Q

Sarcoplasmic reticulum (SR):

A

storage reservoir for Ca2+

59
Q

Release of Ca2+ from SR is controlled by…

A
  • dihydropyridine (DHPR) by electromechanical signal

- IP3 gated Ca2+ channel by pharmacomechanical Gq mechanism

60
Q

Function of SERCA primary transport pump on SR:

A

return Ca2+ to SR

61
Q

Single units are rich in…

A
  • mitochondria

- myoglobin (stores O2)

62
Q

Sarcolemma:

A

Specialized to regulate intracellular Ca2+

63
Q

Ca2+ channels on sarcolemma can be…

A

VG, LG, or MG

64
Q

T/F: VG and MG Ca2+ channels are store independent

A

T

  • Ca2+ source is ECF
  • decrease in Ca2+ leads to decrease in contractions
65
Q

Ca2+ enters cell via…

A
  • store operated Ca2+ channels (SOCC)
66
Q

SOCC is also known as…

A

receptor operated Ca2+ channel (ROCC)

67
Q

SOCC is opened by…

A

intracellular Ca2+ and gets released from storage in SR

68
Q

All the ways to stimulate contraction are…

A
  • myosin linked

- work by increasing intracellular Ca2+

69
Q

Contraction can be stimulated by…

A
  • hormones
  • nerves
  • pacemaker cells
  • drugs
70
Q

T/F: AP is usually needed for contraction

A

F, usually not needed

71
Q

RMP of smooth muscles can be…

A

variable b/c of depolarizing and repolarizing cycles (slow wave potentials)

72
Q

Pacemaker potentials occur via…

A

AP made from threshold being reached

73
Q

Pacemaker potentials are responsible for…

A

rhythmic activity of GI tract

74
Q

For all mechanisms, the amount of contraction is proportional to…

A

levels of intracellular Ca2+

75
Q

3 ways to initiate Ca2+ influx:

A
  • electromechanical coupling
  • pharmacomechanical coupling
  • mechanomechanical coupling
76
Q

Electromechanical coupling is less common b/c…

A

more energy expensive

77
Q

Electromechanical coupling is stimulated by…

A
  • norepi
  • serotonin
  • histamine
  • some drugs
78
Q

Electromechanical coupling acts on…

A

nonCa2+ related channels to generate AP

  • opens L-type VGC Ca2+ in sarcolemma
  • not a lot of VGC Na+
79
Q

Ca2+ for electromechanical coupling comes from…

A

ECF

80
Q

Pharmacomechanical coupling:

A
  • no significant effect on membrane potential

- requires turning on phospholipase C (PLC), which differs depending on the receptor

81
Q

What is the predominant coupling mechanism in vascular smooth muscle?

A

pharmacomechanical coupling

82
Q

How does PLC get activated w/ norepi in vascular smooth muscle?

A
  1. norepi binds to alpha 1 receptor
  2. Gq mechanism activated
  3. alpha q subunit activates PLC
83
Q

How does PLC get activated w/ ADH in vascular smooth muscle?

A
  1. ADH binds to V1 receptors
  2. Gq mechanism activated
  3. alpha q subunit activates PLC
84
Q

How does PLC get activated in GI smooth muscle?

A
  1. Ach binds to M3 receptor

2. beta gamma subunit activates PLC

85
Q

How does PLC get activated in bronchial smooth muscle?

A

paracrine histamine action via Gq

86
Q

How does PLC get activated on uterine smooth muscle?

A

oxytocin binds to class 1 G protein coupled receptor

87
Q

Activated PLC will…

A

cleave PiP2, which turns into DAG and IP3

88
Q

Diacylglycerol (DAG):

A
  • activates PKC

- inhibits MLCP

89
Q

Inositol triphosphate (IP3):

A
  • opens LGC Ca2+ on SER

- liberates Ca2+ from SR

90
Q

What happens to smooth muscle at rest?

A
  • active sites are exposed

- myosin heads aren’t in position to form cross-bridges

91
Q

Steps of contraction:

A
  1. cells stimulated by electromechanical or pharmacomechanical signals
  2. influx of Ca2+
  3. 4 Ca2+ bind to calmodulin (CAM)
  4. MLCK activated
  5. MLCK phosphorylates MLC
  6. myosin heads move to cocked position
  7. cross-bridges form
92
Q

CAM is a…

A

Ca2+ binding messenger protein

- acts as regulatory protein

93
Q

In order for MLCK to phosphorylate MLC, it needs…

A
  • terminal phosphate to be transferred to light chain

- phosphotase enzyme also activated

94
Q

Function of phosphotase enzyme:

A

removes phosphate group

- slow so doesn’t affect contraction

95
Q

Cross bridge cycle:

A
  • similar to skeletal muscle

- cycles slower than skeletal muscle b/c detachment is slow

96
Q

Steps of cross bridge cycle:

A
  1. attachment
  2. rotation of head
  3. detachment
  4. production of force and movement
97
Q

Cross bridge cycle functions as latch bridge b/c…

A

spends most of their time attached

- b/c of this, has low ATP use (1/cycle)

98
Q

Termination of contraction occurs when MLCK…

A

is inactivated by low Ca2+ levels

99
Q

Ca2+ can be removed by…

A
  • SERCA
  • Ca2+ ATPase on membrane
  • Na+/Ca2+ exchanger on plasma membrane
100
Q

Cross-bridges will dephosphorylate by…

A

MLCP, which occurs at much slower rate than phosphorylation

101
Q

During phasic contractions, muscles are most often…

A

at rest

102
Q

Phasic contractions:

A

brief twitch-like contractions in response to single stimulus or brief bursts of stimulus

103
Q

Phasic contractions are equivalent to what kind of contractions in skeletal muscles?

A

isotonic twitch-like contractions

104
Q

Phasic contractions are often associated w/…

A

AP

105
Q

Phasic contractions are usually in organs that…

A

propel/move substances within organ

106
Q

Gut uses phasic contractions by…

A

slow wave AP, which moves food along in periodic contractions

107
Q

The phasic contractions in the gut are activated by…

A

electromechanical activation by pacemaker cells

- opens L-type Ca2+ (DHP channel) on plasmalemma

108
Q

AP in the gut is conducted via…

A

gap junctions

109
Q

Afferent arterioles of the kidney utilizes what type of contraction?

A

phasic

110
Q

Phasic contractions in the afferent arterioles of the kidney are activated by…

A

Ang 2, which in turn activates DHP L-type Ca2+ channels

111
Q

Tonic contractions are…

A
  • most often contracted

- sustained contractions in response to single/continued stimulation by nerves drugs, or hormones

112
Q

Tonic contractions produce…

A

constant tension (aka tone)

113
Q

Level of tone in tonic contractions are set by…

A

concentration of specific chemicals or hormones

- norepi and epi act on alpha 1, which leads to Gq mechanism being activated on sphincters of bladder and GI tract

114
Q

Efferent arterioles of kidney utilizes what type of contractions?

A

Tonic

- Ang 2 stimulates Ca2+ entry via SOCC

115
Q

Tonic contractions are in organs that…

A

have to stay contracted for long periods of time

116
Q

Examples of organs that use tonic contractions:

A
  • bladder
  • sphincters
  • many blood vessels
117
Q

Relaxation of muscles that utilize tonic contraction leads to…

A

increased flow to the area

118
Q

Contraction of muscles that utilize tonic contraction areas leads to…

A

diversion of blood elsewhere

119
Q

Tonic contractions can develop…

A

high forces

120
Q

Tonic contractions can also prevent…

A

movement of substances

- ex: sphincters

121
Q

Relaxation is induced by…

A
  • hormones
  • NT
  • drugs
122
Q

4 ways of relaxation:

A
  • norepi acts on beta 2 coupled to Gi
  • norepi acts on alpha 2 coupled to Gi
  • by-product of cellular metabolisms
  • nitric acid
123
Q

When norepi acts on beta 2, smooth muscle is relaxed during…

A

stress

124
Q

Effects of norepi acting on beta 2 coupled to Gi:

A
  • decreased gut motility
  • delays micturition
  • inhibits labor
  • dilates small arteries to skeletal muscle and coronary arteries
  • bronchodilates
125
Q

When norepi acts on alpha 2 coupled to Gi, what is prevented?

A

sympathetic contraction of smooth muscle

126
Q

Examples of beta 2 agonists that act via Gi:

A
  • clonidine
  • guanabenz
  • guanfadine
  • alpha methyldopa
127
Q

Effects of norepi acting on alpha 2 coupled to Gi:

A

decrease in:

  • cAMP in presynaptic neurons
  • release of norepi
  • contraction
128
Q

By-product of cellular metabolism leads to…

A

decrease in [Ca2+]

129
Q

Examples of by-products that lead to vasodilation:

A
  • adenosine
  • lactic acid
  • increase in K+
  • increase in CO2
  • increase in body temp
  • decrease in O2
130
Q

Nitric acid gets released from…

A

endothelial cells of stressed blood vessels

131
Q

Nitric acid acts on…

A

guanylyl cyclase, which catalyzes GTP and turns it into cGMP

132
Q

Guanylyl cyclase:

A
  • turns off IP3, which inhibits Ca2+ entry
  • activates K+ channels, which leads to hyperpolarization and relaxation
  • activates PKG -> activates MLCP -> dephosphorylates MLC -> relaxation
133
Q

Sildenafil works by…

A

blocking phosphodiesterase removal of cGMP

- more cGMP present = more dilation of penile erectile blood vessels

134
Q

Nitric acid can vasodilate…

A
  • blood vessels directly

- indirectly by inhibiting Ang 2

135
Q

Nitroglycerin gets converted to…

A

NO in blood vessels, which in turn dilates coronary blood vessels

136
Q

Stress relaxation:

A

ability to return to resting force of contraction after stretch

137
Q

Example of stress relaxation:

A

urinary bladder returns to resting force as bladder fills and is stretched

138
Q

Reverse stress relaxation:

A

ability to return to resting force when force drops

Physiology (33 decks)

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