Describe the processes of excitation and contraction within a smooth muscle cell (60%
of marks). Briefly outline the mechanism by which nitric oxide affects smooth muscle
cell activity (40% of marks).
College Answer
Insufficient breadth and depth of knowledge limited candidates’ performance to this
question. Candidates were expected to mention mechanisms of muscle cell membrane
activation (e.g. Ca2+ channel mediated action potential, Pacemaker potential, etc), sources
of rise in intracellular Ca2+, intracellular Ca2+ binding to calmodulin in cytoplasm
Ca2+calmodulin complex binding to, and activation of myosin light chain kinase, energy
dependent myosin cross bridges and cycling and mechanism of smooth muscle relaxation. Nitric Oxide (NO) activates guanylyl cyclise which in turn catalyzes the dephosphorylation of
GTP to cyclicGMP which in turn induces smooth muscle relaxation, and the various
mechanisms by which this occurs..