A postsynaptic neuron has three presynaptic inputs from neurons X, Y, and Z. When X and Y are stimulated simultaneously and repeatedly, the postsynaptic neuron reaches threshold and undergoes an action potential. When X and Z are stimulated simultaneously, however, there is no change in the membrane potential of the postsynaptic neuron. The simultaneous stimulation of X and Y is an example of: Select one: O A. presynaptic facilitation. O B. spatial summation. O C. neuronal divergence. O D. presynaptic inhibition. O E. temporal summation. is/are secreted by the adrenal ---- during chronic stressful conditions to promote the synthesis of glucose from non- carbohydrate substrates. Select one: A. ACTH medulla B. Glucagon cortex C. Glucocorticoids - cortex D. Mineralocorticoids - cortex O E. Epinephrine- medulla