Cardiovascular Physiology Smooth Muscle Flashcards
where is smooth muscle found
around hollow organs such as blood vessels, airways, GI tract, uterus and fallopian tubes, ureters and bladder
what is smooth muscle important in
ocular function, piloerection
what can contraction of smooth muscle cause
propulsion or resistance
is stimulus for smooth muscle intrinsic or extrinsic
can be either
what is smooth muscle regulated by
autonomic neurons, hormones, and autocrine/paracrine signals
describe the smooth muscle cell
smaller cells with single central nucleus
describe the contraction of smooth muscle compared to skeletal muscle
-contractions are slower to develop
-contractions last significantly longer
-maximum force generation greater
-primarily oxidative metabolism
what is the shape of smooth muscle cells
elongated and tapered
does smooth muscle contain T tubules or SR
lacks T tubules and only has rudimentary SR
describe the duration of twitches between all 3 types of muscle
skeletal muscle is shortest and smooth muscle is the longest
what are the 2 types of smooth muscle
-multi unit
- single unit (unitary, visceral)
describe multi unit smooth muscle
-no gap junctions
-each cell responds independently
- muscle behaves as multiple units
-control exerted mainly by nerve signals
- cells function independently
- no tone
describe single unit smooth muscle
-cells connected by gap junctions
-functional syncytium
-control by variety of stimuli
- pacemaker cells
-cells organize into sheets or bundles
-may have tone
what are examples of multi unit smooth muscle
-piloerector muscle
-iris
- ciliary muscles
what are examples of single unit smooth muscle
gut
bladder
uterus
what is an example of a multi unit and single unit smooth muscle cell
blood vessels
what are the contractile elements of smooth muscle
actin and myosin
describe actin in smooth muscle
higher levels and longer than in skeletal/cardiac myocytes
- arranged diagonally to long axis of cell
what does alpha actinin attach to
actin to dense bodies instead of Z line
describe myosin in smooth muscle
-fewer myosin fibers than skeletal/cardiac myocytes
- myosin filaments interspersed with actin
what does calcium bind to in smooth muscle
calmodulin
what are the two actin binding proteins and what do each do
- calponin: inhibits myosin ATPase
- caldesmon: inhibits myosin/actin bond
what needs to be removed from calcium in smooth muscle before contraction can occur
calponin and caldesmon
is smooth muscle organized into sarcomeres
no
what are the requirements for contraction in smooth muscle
-calcium
-ATP
-myosin light chain phosphorylation
what is myosin light chain phosphorylation required for
myosin head to interact with actin
what does myosin light chain kinase do
adds phosphate and begins contraction
what does myosin light chain phosphatase do
removes phosphate and stops contraction
what can smooth muscle contraction be stimulated by
-stretch
-ligands (NTs, hormones, paracrines, autocrines)
-intrinsic activity (pacemaker cells)
where does calcium come from in smooth muscle
mostly extracellular and some intracellular
are action potentials required for contraction
no or depolarization
are smooth muscle cells tonic or phasic
tonic, they are normally contracted and can alter their force of contraction
what is cross bridge cycling in smooth muscle controlled by
a calcium regulated enzyme that phosphorylates myosin
what are the steps of contraction in smooth muscle
- inactive calmodulin -> actin calcium calmodulin
-inactive myosin light chain kinase -> active myosin light chain kinase
-phosphorylation by myosin light chain kinase which forces cross bridge toward thin filament - cross bridge cycling
- myosin light chain phosphatase dephosphorylates and stops contraction
what are the two sources of calcium in smooth muscle
-the SR
- extracellular calcium entering the cell through plasma membrane calcium channels
how is the calcium removed in smooth muscle
-to SR via calcium ATPase
- to ECF via calcium ATPase and sodium/calcium exchanger
how do you vary the force of contraction in smooth muscle
alter the amount of calcium
what is the latch state
tension is maintained in the smooth muscle although calcium levels and ATP usage in the cytosol are low
what is the mechanism for how the latch state occurs
-binding of acetylcholine to muscarininc receptors
- increased influx of calcium into the cell
- activation of calmodulin dependent myosin light chain kinase
- phosphorylation of myosin
- increased myosin ATPase activity and binding of myosin to actin
-contraction
-dephosphorylation of myosin by myosin light chain phosphatase
-relaxation or sustained contraction due to the latch bridge and other mechanisms
which muscle cells can be activated or inhibited
smooth muscle and cardiac muscle
do smooth muscle neurons form synapses
no
what do smooth muscle axons contain
varicosities
where is the NT in smooth muscle released into
interstitial fluid
how does the NT distribute to receptors on smooth muscle cell surfaces
via simple diffusion
do hormones change membrane potential in smooth muscle
may or may not
what is the difference between multiunit and single unit smooth muscle
mutli unit smooth muscle - each cell has its own activation
in single unit smooth muscle - theres only one signal to all cells
what local factors cause smooth muscle activation
paracrine signals, acidity, O2, and CO2 levels, osmolarity and the ion composition of the ECF
what does response to local factors do
alters smooth muscle contraction in response to changes in the muscles immediate internal environment, independent of long distance signals from nerves and hormones
what local factor causes smooth muscle relaxation
nitric oxide
what does stretching do locally to smooth muscle
cause response by contracting by opening mechanosensitive ion channels leading to membrane depolarization
describe pacemaker potentials in smooth muscle
-resting membrane not stable, slow depolarization to threshold
-mechanism unknown
where are smooth muscle pacemaker cells found
in GI tract
what is the only type of muscle that has tone
single unit smooth muscle
which muscle type is unaffected by hormones
skeletal
