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Flashcards in smooth muscle contraction Deck (42):

what is a dense body

a cytoskeletal specialization that the thin filaments are anchored to


out of the following list, which are components of smooth muscle; thin filaments, thick filaments, sarcomeres, dense bodies, A bands, I bands, striations, actin, myosin, T tubules, troponin C?

smooth muscle only has:
thin/thick filaments
dense bodies


explain how smooth muscle is activated

spontaneously as in peristalsis or uterus
excited by nerves-ex vascular smooth muscle
or by stretch


describe a slow muscle twitch (in comparison to skeletal muscle)

slow contraction velocity and slow relaxation but muscle shortening is large
duration of tension is usually longer- tonic contractions


list 5 things that are contained within a caveoli in a smooth muscle cell

-Muscarinic ACh receptors
-Adrenergic receptors
-L type calcium channels
-ATP sensitive potassium channels
-Calcium sensitive potassium channels


when describing skeletal muscle vs smooth muscle action potentials, are both Na+ dependent? If not, what are they?

NO! skeletal muscle is Na+ dependent but smooth muscle is calcium dependent


compare the cross bridge cycle timing in smooth muscle vs the cycle in skeletal muscle

The proportion of time spent in the tension generating phase of the cross bridge cycle is longer for smooth muscle than that of skeletal muscle thus resulting in greater force of smooth muscle contraction with less energy expenditure (ATP hydolysis)


compare the percentage shortening in skeletal and smooth muscle

Smooth muscle can contract to less than 1/3 of its stretched length where as skeletal muscle only contracts about 1/4-1/3 of its stretched length


what are the names of the two units that smooth muscle can be divided into?



is the statement below describing unitary or multiunit smooth muscle;
"coupled via gap junctions, can be spontaneously activated"



give 3 examples in the human body of multiunit smooth muscle

-smooth muscle fibers in the ciliary and iris of the eye
-piloerector muscles that cause hair erection
-airway smooth muscle
(also some arteriolar muscle)


give 4 examples in the human body of unitary smooth muscle

-small blood vessels
-GI tract
-most arterial muscle


out of smooth muscle, skeletal muscle and cardiac muscle, which utilize 2 sources for Ca?

smooth and cardiac muscle


what would be the effect of L-type calcium channel blocking drugs?

decrease influx of calcium, and reduce contractile activity in both smooth and cardiac muscle


what are the two ways that calcium is removed from the sarcolemma?

-By Ca++ pumps in the SR membrane and in the sarcolemma
-And by 3Na/ca exchange across sarcolemma


what is capactive calcium entry?

the SR is refilled by calcium from outside the cell- this seems to occur in a way that entering calcium does not trigger a contraction
this can occur when the SR calcium stores become depleted


if there is no troponin C in smooth muscle, how is contraction triggered?

by calcium activation of myosin light chain kinase (MLCK)


where does calcium bind when initiating an AP in smooth muscle?

to calmodulin which is on the MLCK


what is MLCP

a soluble phosphatase in the sarcoplasm that desphosphorylates the regulatory light chain of myosin


what are the two categories of smooth muscle contraction?



list the 4 steps leading to contraction that both the electromechanical and the pharmacomechanical categories of smooth muscle contraction lead to

1. increase in intracelluar ca
2. CICR (ca induced ca release)
3. ca++ calmodulin activation of MLCK
4. activation of smooth muscle myosin
5. contraction


what type of contraction pathway does an action potential or stretch stimulate?



when is the pharmacomechanical pathway activated?

ligand binding to cell surface receptor


what is basal electric rhythm (BER)?

refers to waves of rhythmic depolarization of intestinal smooth muscle cells, which originate at a specific point and then are propagated along the length of the GI track


what can BER control?

BER controls the maximal frequency of contractions, their propagation velocity and the direction in which they propagate


can BER initiate action potentials?

it is only when there is a release of neurotransmitters from enteric nerve endings that are superimposed on the BER waves that an AP can occur


what is the name of the additional step that is seen in the crossbridge cycle of smooth muscle but not that of skeletal muscle?

the "latch" state


how is the latch state mechanism theorized?

It is thought that this state occurs because: the MLCP dephosphorylation of the myosin light chain occurs while the myosin head IS bound to actin


what is ET-1

amino acid peptide produced by vascular endothelium
its formation and release are stimulated by angiotension II, ADH, thrombin, cytokines, reactive oxygen species and shearing forces acting on vascular endothelium


explain the effects of initial activation of ET-1b

causes formation of NO which then causes vasodilation and hypotension


explain the cardiovascular effects of endothelin (ET-1)

initially vasodilation and hypotension (ET-1b) followed by prolonged vasoconstriction and hypertension (smooth muscle ETa and ETb activation)


list some diseases or conditions associated with elevated endothelin

coronary vasospasm
heart failture


which receptor binds epinephrine to stimulate contraction?

alpha 1 receptor


which receptor binds epinephrine to stimulate relaxtion?

beta 2 receptor


how is local blood flow controlled acutely?

via rapid changes in vasodilation or vasoconstriction


what are the two theories that may account for active hyperemia?

-oxygen lack theory: low O2 causes smooth muscle relaxation of the sphincter
-vasodilatory theory: substances (adenosine) are released by active muscles which cause relaxation of the sphincter


what is hyperemia?

when the rate of blood flow through a tissue becomes increased in response to the tissue's high activity


explain the mechanism of A2 adenosine receptors

they couple to Gs leading to adenylate cyclase stimulation and an increase in camp and PKA activity


explain the mechanism of A1 adenosine receptors

can couple to ATP sensitive K+ channels causing smooth muscle hyperpolarization and a decrease in calcium influx (shuts calcium channels down)


what is 1 difference and 1 similarity between adenosine and adrenergic receptors?

they are DIFFERENT proteins encoded by DIFFERENT genes
but they are both G-coupled receptors that can activate or inhibit similar downstream pathways


what is stress relaxation

certain areas of smooth muscle (ie bladder) can have a decline in pressure over time at a constant volume strain
the amount of stress relaxation a smooth muscle can undergo is related to its amount of elastin


name two neurotransmitters that have been identified in the vaso-vagal "receptive response" mechanism

nitric oxide