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A&P Smooth Muscle
| Question | Answer |
|---|---|
| T/F - Smooth muscle lacks troponin | T |
| Troponin is the regulatory protein in cardiac and sk muscle as ______ is the regulatory proteins in smooth muscle | Myosin light chain kinase (MLCK) and myosin light chain phosphatase (MLCP) |
| These regulate the rate of myosin ATPase activity | Calponin and Caldesmon |
| In what fashion are smooth muscle filaments oriented | diagonal |
| Z lines/proteins are to SK muscle and cardiac muscle as _____ is to smooth muscle | dense bodies (filaments are anchored here) |
| T/F - The T-tubules in smooth muscle allow the propogation of the AP | false - no T-tubules. Cells are very small - no need for T-tubules |
| What volume of Ca++ stores do smooth muscle have | very little (relies on extracellular Ca++) |
| T/F - smooth muscle cells have gap junctions | true |
| Examples of single-unit smooth muscle | GI, uterus, urinarry bladder |
| T/F - Single unit smooth muscle are highly innervated with few gap junctions | false - few innervations and many gap junctions |
| Multiunit smooth muscle is ______ innervated and has ______ gap junctions | highly, few |
| contractile strength of multiunit smooth muscle is dependent upon what? | number of fibers stimulated and frequency of stimulation (similar to skeletal muscle) |
| examples of multiunit smooth muscle | iris, arteries, smooth airways |
| 3 things that trigger smooth muscle contraction | electrical depolarization, chemical stimuli (hormones, metabolites, etc), stretch (mechanical stimuli) |
| Electrical depolarization of cell involves what what kind of receptor | L-type voltage-gated Ca++ channels |
| two types of smooth muscle action potentials | spike, plateau |
| the prolonged contraction of the uterus is an example of what kind of smooth muscle action potential | plateau |
| What causes pacemaker depolarization of smooth muscle | Ca++ leaking into cell from always-open channels |
| example of a functional use for smooth muscle pacemaker depolarization | rhythmic contractions of the GI |
| What kinds of channels detect when SR Ca++ levels are low - and what does this trigger | Store-operated channels, triggers extracellular influx of Ca++ |
| The release of Ca++ from the SR in smooth muscle is mediated by what | IP3 (Inositol trisphosphate) which binds to a receptor on the sarcoplasmic reticulum, RYR receptors |
| the two regulatory proteins Calponin and Caldesmon are regulatory in what way | modulate the activity of ATPase at the head of myosin |
| T/F - smooth muscle does not need an action potential to contract | true |
| How does calcium enter the smooth muscle cell | voltage-gated L-type channels, Store-operated channels, Release of Ca++ from the SR by cholinergic stimulation |
| Ca++ release from the sarcoplasmic reticulum happens how | calcium induced, IP3 (second messenger) |
| IP3 is produced by activation of what kind of receptor | Muscarinic GPCR aQ - which is coupled with phospholipase C |
| Once calcium levels increase in the smooth muscle cell, calcium is going to bind to _______ | calmodulin |
| Calmodulin, after it is bound by calcium is going to be responsible for activating _______ | Myosin light-chain kinase (MLC kinase), Calcium/calmodulin dependent kinases (additional enzymes) |
| Myosin light-chain kinase is going to phosphorylate ______ | Myosin light-chains (on the heads of myosin), |
| phosphorylating myosin light-chains is going to do what | activate the myosin head |
| Calcium/calmodulin dependent kinases is going to be responsible for what? | phosphorylating calponin |
| phosphorylation of calponin does what? | decreases its inhibitory action on ATPase |
| calponin does what? | inhibits ATPase |
| Norepinephrine binds to a _________ receptor on the smooth muscle | aS GCPR |
| activation of phospholipase C by the aQ leads to the production of what | diacylglycerol (DG), IP3 |
| production of diacylglycerol (DG) activates what product | protein kinase C (PKC) |
| what does protein kinase C (PKC) do | sensitizes the cell to calcium-mediated events (the cell is going to be very sensitive to the cytosolic calcium) |
| relaxing the smooth muscle is done how | removing the phosphate from MLC using myosin light chain phosphatase, reabsorption of calcium in the sarcoplasmic reticulum, pumping calcium out of the cell, NE stimulation |
| T/F - myosin light chain phosphatase is always turned on | true |
| regulating myosin phosphatase is done how | phosphorylation by Rho-kinase - which inactivates myosin phosphatase |
| T/F - hormones can lead to either contraction or relaxation of smooth muscle | true |
| Increased cGMP (cyclic GMP) leads to increased _______, which in turn, leads to what? | Protein Kinase G (PKG), reduced calcium levels and sensitivity of the contractile system to Ca++, and increased MLCP activity |
| T/F - smooth muscle has a rapid cross bridge formation and cycling rate | false - slow cross bridge formation and cycling rate (very efficient) |
| Smooth muscle maintains tension for _______ periods of time | long |
| T/F - Smooth muscle has low energetic needs | true |
| Smooth muscle has an _______ tension as length increases | increased |
| Smooth muscle does what in the presence of stretch | contracts |
| T/F - smooth muscle needs an action potential to contract | false |
| T/F - Nitric oxide has a direct effect on smooth muscle relaxation | false - indirect |
| ATPase activity is where | the head of myosin |
| What form of calcium channels are found in the calveoli | L-type voltage-gated calcium channels |
| Intracellular calcium is released how | stimulation by IP3 or RYR activation (by Ca++) |
| Trace the chain reaction of sympathetic stimulation | NE -> GCPR aS -> increase adenylyl cyclase -> increase cAMP -> increase PKA -> (p)(inhibition) MLCK -> sm muscle relaxation |
| Trace the chain reaction of parasympathetic stimulation | Acetylcholine -> GCPR aQ -> phospholipase C -> IP3 -> release of Ca++ from SR -> sm muscle contraction |
| Trace the EXTRA chain reaction of parasympathetic stimulation which aids to Ca++ sensitivity | Acetylcholine -> GCPR aQ -> phospholipase C -> DG -> Protein Kinase C -> + smooth muscle sensitivity to Ca |
| Once Ca++ is in the cell, trace the steps that lead to MLC | Calcium Calmodulin (CaCm) -> MLCK -> (p) MLC -> muscle contractility |
| Once Ca++ is in the cell, trace the steps that lead to ATPase increase | Calcium Calmodulin (CaCm) -> CaCm dependent kinases -> (p)(inhibition) Calpone -> +ATPase activity |
| Trace the steps leading to erection | Ca++ -> CaCm -> NO synthase -> NO -> Guanylyl cyclase -> PKG -> increased MLCP, reduced Ca++ sensitivity, reduced cytosolic Ca++ concentration |
| In skeletal muscle, activation of ryanodine receptors occurs via a ______, whereas, in cardiac and smooth muscle, the primary mechanism of activation is _______ | physical coupling to the dihydropyridine receptor (a voltage dependent L-type calcium channel), calcium-induced calcium release |
| T/F Multi-unit Smooth muscle contracts with stretch | F - only unitary |
| Multiunit smooth muscle is under _____ control | central |
| Unitary smooth muscle is under _____ control | Local |
Created by:
mmw562