Suppose that both stimuli seen in these graphs happened equa

Suppose that both stimuli seen in these graphs happened equally at the same time on a postsynaptic membrane as a result of two different synapses. Which of the following best describes the result?

A. No chemically gated ion channels would open.

B. Temporal summation would occur.

C. There would be little or no graded potential.

E-55 E-70 Threshold Stimulus 10 20 Time (ms) E-55 70 Threshold Stimulus 10 20 Time (ms)

Solution

Option A is incorrect. Without opening of ion channels membrane potential cannot change after application of stimulus.

Option B is also incorrect. Temporal summation results in action potential, but in the above cases, there is no possibility of action potential at all. Likewise, option D is also incorrect.

Option C is the correct answer. A little bit of graded potential may or may not be there. While one stimulus will depolarize the membrane slightly, the other one will slightly hyperpolarize it. As a result, the membrane will remain in its original state itself, without any change. Please note that graded potentials are small changes in membrane potentials which arise due to summation of actions of multiple (in this case, two) stimuli.