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54 Cards in this Set
- Front
- Back
Where is smooth muscle located?
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the majority is in walls of hollow organs and tubes
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What are 2 unique problems smooth muscle is responsible for?
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1. Being able to contract over a wide range of lengths.
2. Being able to contract for sustained periods of time. |
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what innervates smooth muscle?
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autonomic nerves
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what's unique about autonomic innervation?
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-the axon lays across the muscle cells.
-no real terminal. -receptors are farther away so NT has to diffuse further. |
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what's the name for the point analogous to a nerve terminal?
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Varicosity
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of smooth muscle, what is the characteristic
-shape -size -nucleus |
shape = spindle
nucleus = one size = smaller than skeletal |
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compared to skeletal muscle is smooth more or less developed?
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less
-doesn't extend length of muscle -has SR, but no t-tubules. |
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are smooth muscles coupled
-mechanically -electrically |
Yes - both.
Mechanical: conected so all contract together. Electrical: most coupled through gap junctions to behave as a single unit. |
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what are 5 characteristics of smooth myofilaments?
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-smooth, not striated
-longer thick filaments -thin filaments have no troponin -Intermediate filaments -Dense bodies |
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what's different about
-thick filaments -thin filaments and why? |
thick: longer to allow more tension to develop over longer length.
thin: contain no troponin because tropomysin doesn't cover the binding site for myosin. |
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what are
-intermediate filaments? -dense bodies? |
int. fils = structural proteins that support the cell's shape.
dense bodies = analag. to Z lines - hold Actins together |
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what are the two types of smooth muscle units?
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-single unit
-multi unit |
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what is multiunit smooth muscle?
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-multiple, discrete units that function independently.
-stim by nerves separately. |
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what are some sites of multi-unit smooth muscle?
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lens adjusters, iris, base of hair follicles, large airways, large blood vessels.
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what is single-unit smooth muscle?
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-muscle that acts as one single unit; contracts together.
-gap junctions couple together. -myogenic |
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what does myogenic mean?
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refers to muscle that needs no nervous stimulation; self-excitable - smooth musc is.
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where is single-unit smooth muscle found?
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-GI tract
-small blood vessels -reproductive/urinary tract walls |
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what are the steps in smooth muscle cross-bridge cycling?
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1. Ca2+ binds calmodulin
2. Calmodulin/Ca binds myosin lightchain kinase (MLCK) 3. MLCK phosphorylates myosin crossbridges 4. Cross-bridges bind actin 5. Crossbridge shortens/tense |
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how does the cross-bridge cycling get stopped?
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when calcium is taken back up into both sources.
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what is the result of calcium re-uptake?
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MLCP - phosphatase - takes the phosphate off myosin crossbridge.
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what are the two sources of cytosolic calcium for crossbridge cycling?
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-sarcosplasmic reticulum
-exctracellular calcium |
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what are 3 things that can cause smooth muscle membrane activation?
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-spontaneous electrical activity
-nerves and hormones -local factors |
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does smooth muscle have a resting membrane potential?
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no; it depends on the site of the membrane you're looking at.
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what are 2 characteristics of smooth muscle electrical activity?
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-Pacemaker potentials
-Slow waves - the mp oscillates, and can be at different levels depending on time/factors. |
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what do nerves and hormones to to smooth muscle?
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-change the baseline resting potential by changing calcium levels.
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what 3 ways do nerves and hormones alter calcium levels?
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1. depolarizing and causing an action potential.
2. opening voltage-gated Ca2+ channels. 3. Activating G-proteins to cause IP3 generation |
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what does IP3 do to smooth muscle?
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nerves/hormones activate G proteins to generate IP3, it then makes the sarcopl. retic release calcium.
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Are action potentials necessary for smooth muscle contraction?
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NO!
-can use voltg-gtd Ca2+ channels -can use Gproteins/IP3 |
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what 3 local factors can change to activate smooth muscle?
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1. acid - pH decrease
2. O2 levels 3. Stretching -can constrict or dilate bronchial muscle; cause intestinal constractions |
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is there recruitment in smooth muscle contraction? why?
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no
b/c they are already all contracting together as one unit. |
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does the cytosolic calcium level alter?
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yes - by the control mechanisms noted before; allows for greater/lesser strengths of contractions.
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how is the length-tension relationship in smooth muscle compared to skeletal?
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tension increases over much broader lengths.
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define the pacemaker potential
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after an action potential, the resting membrane continues to depolarize until threshold, then into action potential again.
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what type of smooth muscle units are electrically coupled?
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single unit
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how are cells in smooth muscle arranged?
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NOT striated; no sarcomere pattern!
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why are thick filaments in sm. muscle LONGER than skeletal?
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so they can develop tension over a longer range; actin and myosin filaments don't collide as soon.
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is myosin light chain phosphatase always active or no?
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always - just when calmodulin binds calcium is MLCkinase active enough to phosphorylate the myosin crossbridge.
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what allows calcium reuptake into the SR and extracellular fluid?
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Calcium ATPase
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what is the major difference between single and multi-unit smooth muscle?
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multi = needs nerve stimulation
single= self-excitable, doesn't require nerve stimulation! |
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what is neurogenic muscle?
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muscle requiring nerve stimulation
-skeletal, multi-unit smooth |
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what is myogenic muscle?
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muscle that is self-excitable
-smooth |
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does smooth muscle have troponin?
tropomyosin? |
no troponin
yes, tropomyosin, but it has no role. |
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in smooth muscle, what is the molecule analagous to troponin?
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calmodulin kind've.. at least it's what is active first.
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how is electrical activity spontaneously generated in smooth muscle cells?
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by pacemaker potentials.
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what is the resting membrane potential of smooth muscle?
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constantly fluctuating.
About -50 mV at baseline. When very negative, causes a pacemaker potential to depolarize the membrane. |
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does smooth muscle have T tublules?
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NO
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does smooth muscle have troponin?
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no
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what is in place of troponin?
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calmodulin
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where does calcium come from in smooth muscle?
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-Sarcoplasmic reticulum
-extracellular fluid |
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what couples smooth muscle cells electrically?
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GAP JUNCTIONS
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what will increase excitation of smooth muscle cells?
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anything causing an increase in intracellular calcium
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in smooth muscle, how many actin thin filaments are there for every thick filament?
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eleven - 11
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what allows for calcium reuptake?
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Calcium ATPase - works to reuptake into both SR and extracellular
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how do nerves and hormones alter contractile activity of smooth muscle?
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by releasing (at varicosities for nerves) near muscle cells, and causing inhibition or excitation of the cells.
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