10 Smooth Muscle Flashcards
phasic contraction
contraction followed by relaxation
tonic contraction
sustained contraction
features of smooth muscle (5)
1/ uninuclear 2/ no striations 3/ no T-tubules 4/ lots of caveolae 5/ numerous cell-to-cell junctions
dense bands from adjacent cells combine to form
intermediate junctions (mechanical coupling) - for transmission of force between cells
a gap junction provides
electrical (ionic) coupling
major storage site for Ca2+ ions in smooth muscle
SR
2 receptors in the SR
IP3 and ryanodine
binding of IP3 to its receptors allows
release of intracellular Ca2+ needed for contraction
three types of myofilaments in smooth muscle
actin, myosin, intermediate
thin filaments contain
actin, tropomyosin
calponin, caldesmon
NO TROPONIN!
instead of troponin, smooth muscle has
calponin and caldesmon
thick filaments are composed of
two heavy chain subunits
two light chain subunits
intermediate filaments are
a cytoskeletal component
neurotransmitters that cause contraction
excitatory transmitters
neurotransmitters that cause relaxation
inhibitory transmitters
these are also not present in smooth muscle
NMJs
multi-unit smooth muscle
- neurogenic (requires nerve stimulus to initiate contraction, like striated muscle)
- walls of large blood vessels, large airways of respiratory tract, eye muscles
single unit (unitary) smooth muscle
- arranged in sheets; sheets act as a single unit
- sparsely innervated
- electrically coupled via gap junctions
pacemaker regions contain these special cells
Interstitial cells of Cajal (ICC)
cross-bridges (for sliding filament mechanism) project from the ___ filaments
thick filaments
myosin light chains must be ____
phosphorylated
this enzyme is responsible for myosin phosphorylation
myosin light chain kinase (MLCK)
myosin light chain kinase (MLCK) requires these two things for activity
calcium and calmodulin
this initiates smooth muscle contraction
calcium-dependent phosphorylation of myosin light chain
MLC dephosphorylation occurs via
myosin light chain phosphatase (MLCPase)
for smooth muscle contraction, increase this, decrease that
increase MLC-p
increase MLCK
decrease MLCPase
for smooth muscle relaxation, increase what decrease what
decrease MLCK
decrease MLC-p
increase MLCPase
increased cytosolic ____ activates myosin light chain kinase (MLCK)
calcium
electro-mechanical coupling is when
depolarization of the membrane leads to opening of voltage-gated Ca2+ channels, followed by increase in cytosolic Ca2+
these receptors on the SR are stimulated to release more Ca2+ via calcium-induced-calcium release
ryanodine receptors (RyR)
pharmaco-mechanical coupling of smooth muscle
binding of an agonist on the membrane leads to elevation in cytosolic Ca2+ without any change in membrane electrical potential
pharmaco-mechanical pathway involves
G-q (heterotrimeric G protein)
PLC-B1
IP3
DAG
in the pharmaco-mechanical pathway, IP3 binds to its receptor ____ on the SR which does this:
IP3R, to release calcium
smooth mm relaxation results from reduction in cytosolic ____
calcium
second messengers involved in smooth muscle relaxation
cAMP and cGMP
For smooth muscle relaxation, cAMP is stimulated by
B-adrenergic activators (adrenalin)
for smooth muscle relaxation, cGMP is stimulated by
NO
