Smooth muscle contractions Flashcards
Duration of a smooth muscle contraction depends on…
length of the Ca gradient
prolonged stimulus of a tonic smooth muscle by NE or Epi leads to…
isotonic contraction, but with less Ca and therefore less ATP cycling, the contraction becomes more energy economical
phasic smooth muscle cells will respond to sequential stimuli by…
summing their Ca concentrations to increase contraction force as more MLCK is activated by calmodulin
greater concentrations of ACh cause smooth muscle to…
experience greater response (stronger contraction for longer)
relative to skeletal muscle, the force-velocity curve for smooth muscle is…
lower, due to less actin activated ATP-ase activity
relative to skeletal muscle, the length-force relationship curve of smooth muscle is…
broader, due to the short myosin heads, and long actin filaments; physiologically sensical since smooth muscle covers organs that expand
cGMP role in smooth muscle
arg->nitric oxide (by calmodulin/Ca + nitric oxide synthase) -> guanyl cyclase -> cGMP -> inhibits smooth muscle contraction (lowers intracellular Ca)
cGMP activates? which does…
cGMP activates cGMP dependent protein kinase
cGK ->
1) opens K channels, which hyperpolarizes the cell and stops L-type Ca channels
2) activates IP3 receptor associated Gkinase (IRAG) which blocks IP3 receptors
3) +p to the myosin binding subunit of myosin light chain phosphatase (MLCP) which activates it
cAMP in smooth muscle
when activated by Gs subunits of GPCR’s that are beta-adrenergic receptors, it causes a drop in intracellular Ca levels
muscles in the penis responsible for erections…
trabecular muscles (relax during erection)
arteries in the penis that feed from the cavernous (deep) artery of the penis
helicine arteries
PDE-5
phosphodiesterase that breaks down cGMP - inhibited by sildenafil
neurogenic erectile dysfunction
common for the cavernous nerve to be damaged in radical prostatectomies or other surgeries on the rectum/bladder
improved technique is available
arteriogenic ED
hyperlipidemia/hypertension; endothelial dysfunction
venogenic ED
1) presence of extra venous channels in the cavernosum
2) trauma to the tunica albunginea (which the veins are pressed against)
3) insufficient trabecular muscle relaxation - often due to excessive adrenergic tone
