Smooth Muscle Flashcards
What is the shape of smooth muscle cells?
short, fusiform
do smooth muscle cells have a sarcomere?
no- smooth muscle has no striations= no sarcomeres
how many nuclei does smooth muscle have
smooth muscle has one-centrally located nucleus
does smooth muscle still have actin and myosin?
yes
Why in a smooth muscle cell is the major source of calcium external?
because it has less sarcoplasmic reticulum
in smooth muscle cells are the thin filaments attached to Z lines?
no- they are attached to dense bodies
Is innervation apparent in smooth muscle cells?
yes- there are nerve fibers that are attached to bundles of smooth muscle cells
What is different in the arrangement of myosin and actin in smooth muscle
the actin is longer
Smooth muscle cells are linked together by…
attachement plaques (like adhering junctions)
describe the myosin ATPase activity of smooth muscle cells
it is much slower
what does the myosin light chain do?
it regulates the ATPase behavior of myosin head
the longer actin and myosin filaments push in which direction?
antiparallel
What is the calcium sensor in smooth muscle cells
calmodulin
How many calcium channels do smooth muscles have
3; RyR, IP3, and calcium channels from the outside (surface L-type calcium channels)
What does a kinase do
phosphorylates
What does myosin light chain kinase do and how is it activated?
it is activated by Ca2+ -calmodulin; it phosphorylates the myosin light chain
What happens when MLCK phosphorylates light chains in myosin heads?
increases the myosin ATPase activity
What does a phosphatase do?
pulls phosphate off, relaxes muscle
What does kinase use as its source of phosphate
ATP (hydrolysis)
Where does smooth muscle rest?
-50
Pharmacomechanical Coupling
occurs when chemical signals change muscle tension through signal transduction pathways with little to no change in membrane potential
What is the first messenger for a metabotropic receptor?
Receives signal on the outside (something like a drug, hormone or a neurotransmitter)
What is an example of a second messenger (metabotropic)
IP3 (small molecules that initiate and coordinate intracellular signaling pathways)
What can modulatory pathways do (smooth muscle)
alter the activity of MLCK or phosphatase
What effect does nitric oxide have on Ca2+ in the smooth muscle cells
pumps more calcium into the sarcoplasmic reticulum -> causing contraction
Compare to the other muscle cells, smooth muscle cells are (describe their contraction)
the slowest to contract and to relax
