Question

A presynaptic nerve terminal releases a neurotransmitter that activates K+ conductance in the postsynaptic membrane. If the postsynaptic cell body had an initial voltage of -65 mV and ENa = +70 mV, ECl = -70 mV and EK = -90 mV, the new postsynaptic voltage will be:

a) Between 0 mV and +70 mV
b) Between 0 mV and -70mV
c) Between -70 mV and -90 mV
d) More negative than -90 mV
e) -70 mV

Answer 1

When K+ conductance is activated in the postsynaptic membrane, the voltage moves towards the equilibrium potential of K+, which is -90 mV. Therefore, the new postsynaptic voltage will be between -70 mV and -90 mV.

Step-by-step explanation:

If a presynaptic nerve terminal releases a neurotransmitter that activates K+ conductance in the postsynaptic membrane, the postsynaptic voltage will change based on the equilibrium potential of K+ (EK = -90 mV). Since the initial voltage of the postsynaptic cell body is -65 mV and activation of K+ conductance generally leads to an efflux of K+ ions, making the inside of the cell more negative, the new postsynaptic voltage will tend toward EK.

The correct answer is, therefore, c) Between -70 mV and -90 mV, as the postsynaptic voltage will become more negative than the original -65 mV, moving in the direction of the equilibrium potential for potassium ions, which is -90 mV, but not more negative than EK.