Smooth Muscle II Flashcards
(30 cards)
How does smooth muscle contraction start
increase in intracellular Ca++
what is the primary source of Ca++ for smooth muscle
extracellular
what happens when intracellular Ca++ is increased
binds to calmodulin
what does calmodulin-Ca++ do
bind to and activated MLCK
what does MLCK do
phosphorylates myosin and allows for activation of myosin ATPase, thus binding of actina nd myosin
how long can the attachment-detachment cycle using ATP continue
as long as myosin is phosphoryalted
what is different about ATPase in smooth vs. skeeltal muscle
it’s not always active in smooth muscle
decreased MLCk activation and myosin phosphatease activity can lead to what
relaxation of tonic contraction
what is happening in relaxation o fmuscle
intracellular Ca++ decreases
you get dephosphorylation of myosin by myosin phosphase
what happens in latch bridge
low MLCK, ATPase, and myosin phosphatase activity
cross-bridge is maintained in contracted state
think of it like a very slow power stroke
difference of smooth muscle contraction in comparision to skeletal muscle
smooth muscle has long, tonic contractions that can occur for hours or days
difference of smooth muscle energy
low energy to produce same tension as in skeletal muscle due to cross-bridge characteristics
stress-relaxation response of smooth muscle
happens in response to stretching/filling to maintain constant pressure (bladder)
why is the onsut and duration of smooth muscle relatively long
due to rate of atin/.myosin attachement/detachment and availability of Ca++
does smooth muscle have structured NMJ?
no
how are nerve fibers arranged on smooth muscle
diffuse branches of merve fibers lie over sheets of smooth muscle
what does smooth muscle have instead of end-feet
nerve fiber has multiple varicosities along the axes of a nerve fiber
diffuse junctions
nerve fiber does not direcetly contact smooth muscle
contract junctions
nerve fiber does contact smooth muscle in multi-unit smooth muscle
in general if acetylcholine excites a tissue waht will NE do
inhibit it
electromechanical stimulation event
open up Ca++ channels and cause contraction
electromechanical inhibition effect
close Ca++/Na+ channels or open K+ channels in order to cause a hyperpolarization and inhibit
pharmacomehcanical stimulation
you don’t have to have a change in membrane potential in order to get contraction
what are teh 2 sources of Ca++ in smooth muscle
extracellular fluid (primary) sarcoplasmic reticulum
