Questions: QUESTION 21 How much of a change in the membrane potential is necessary for the summation of postsynaptic potentials to result in an action potential being generated? +10 mV -30 mV +30 mV -100 mV +15 mV QUESTION 22 A channel opens on a postsynaptic membrane that causes a negative ion to enter the cell. What type of graded potential is this? repolarizing non-polarizing summating hyperpolarizing depolarizing

Question 21:

The answer is the last one: $+15 \mathrm{mV}$.

Explanation:

• An action potential is typically generated when the membrane potential reaches a threshold level. In most neurons, this threshold is around -55 mV. The resting membrane potential is usually around -70 mV. Therefore, a change of approximately +15 mV is necessary to reach the threshold from the resting potential.
• $+10 \mathrm{mV}$: This change might not be sufficient to reach the threshold from the resting potential.
• $-30 \mathrm{mV}$: A negative change would move the membrane potential further from the threshold, not closer.
• $+30 \mathrm{mV}$: This change is more than necessary to reach the threshold, but the minimum required change is +15 mV.
• $-100 \mathrm{mV}$: A negative change of this magnitude would hyperpolarize the membrane, moving it far from the threshold.

Question 22:

The answer is: hyperpolarizing.

Explanation:

• Hyperpolarizing: When a negative ion enters the cell, it makes the inside of the cell more negative, which is characteristic of a hyperpolarizing graded potential.
• Repolarizing: This term refers to the return of the membrane potential to its resting state after depolarization, not applicable here.
• Non-polarizing: This is not a standard term used to describe graded potentials.
• Summating: This refers to the process of adding up multiple graded potentials, not the type of potential itself.
• Depolarizing: This occurs when the membrane potential becomes less negative (more positive), which is not the case when negative ions enter the cell.