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20 Cards in this Set
- Front
- Back
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Mechanism of contraction of Smooth Muscles.
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Similar to skeletal muscles even in the absence of sarcomeres. Myosin moves along actin filaments
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Visceral Smooth Muscles. Do they need nerves? Where are they found?
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Do not need nerves to function, found in resistance arteries and organs such as the bladder and intestines
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Multiunit Smooth Muscles. Where are they located? Do they need nerve stimulation?
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located some distance from each other and have collagen between them. Located in large blood vessels, the iris of the eye and the piloerector muscles in the skin
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Describe the microanatomy of the Smooth Muscle.
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No striations, no sarcomeres
Have actin, myosin and gap junctions |
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Regulation of Smooth Muscle contraction.
What is binding of myosin to actin dependent on? |
Phosphorylation of myosin light chains
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Regulation of Smooth Muscle contraction.
What allows for the relaxation of myosin from actin (which enzyme)? |
Myosin phosphatase
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What determines the degree of contraction of smooth muscles?
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the ratio of activated kinase (MLCK) over phosphatase
MLCK/phosphatase |
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What activates MLCK? And what does MLCK stand for in the first place?
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Calmodulin activates MLCK which is myosin light chain kinase
Calmodulin itself is activated by Ca++ |
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What two Ca++ "movers" are found in smooth muscles?
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Na+/Ca++ exchangers, and Ca-ATP-ase
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What can reduce contractile tone of the smooth muscles?
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cAMP-dependent protein kinase (PK phosphorylates MLCK, which inhibits MLCK's combination with the Ca2+ - calmodulin complex
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What is the effect of Norepinephrine on the smooth-muscle contraction system?
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Norepinephrine binds to the alpha-adrenergic receptors and opens calcium channels --> depolarization
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What is the effect of Epinephrine on the smooth-muscle contraction system?
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Epinephrine binds to the beta-adrenergic receptors and via GTP causes activation of cAMP
cAMP -> protein kinase -> phosphorylation of MLCK Phosphorylation of MLCK leads to DECREASED CONTRACTILE TONE |
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T/F Sarcomeres are present in the smooth muscles
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False
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T/F Smooth muscles contain troponin
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False
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T/F Myosin phosphorylation is important in Smooth Muscle contraction
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True, it is a major site of control
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T/F T-tubules are absent in the smooth muscle
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True
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T/F SR is present in smooth muscle
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True
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T/F Phospholamban is present in the smooth muscle
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False
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T/F Na-Ca Exchange is present in the smooth muscle
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True
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What is the function(s) of nerves in smooth muscles?
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Nerves can control or modulate activity in the smooth muscles
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