The marianas trench, where the pacific plate descends under the leading edge of the eurasian plate, is the deepest sea floor in the world. these ocean trenches form when two oceanic plates collide a) and the younger, less dense of the two plates rides over the edge of the older plate. b) and the younger, denser of the two plates, rides over the edge of the older plate. c) when convection currents in the mantle force the older plate downward. d) and the plates are approximately the same age and density.

Choose the incorrect statement (a) the motor end plate membrane is only capable of generating graded potentials, but it is contiguous with the skeletal muscle sarcolemma, which can generate action potentials. (b) propagation of an action potential through the t-tubules into the sarcoplasmic reticulum triggers the release of ca++ into the cytoplasm of a skeletal muscle fiber. (c) the generation of suprathreshold endplate potentials in multiple muscle fibers could be due to the increased frequency of action potential generation at the axon hillock of a single motor neuron. (d) a greater amount of ach would be found in the presynaptic vesicles of a motor unit that fired several action potentials after exposure to botulinum toxin, than in a motor unit that fired several action potentials after exposure to the venom of the krait snake (which contains α-bungarotoxin).