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