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) more negative than -90 mV
B) between -70 mV and -90 mV
C) between 0 mV and -70mV
D) between 0 mV and +70 mV
E) -70 mV

Answer 1

The new postsynaptic voltage will be between -70 mV and -90 mV because the activation of K+ conductance will drive the membrane potential towards EK (-90 mV) without exceeding it.

Step-by-step explanation:

When a presynaptic nerve terminal releases a neurotransmitter that activates K⁻¹ conductance in the postsynaptic membrane, the resulting effect is typically to either hyperpolarize or stabilize the membrane voltage. In this scenario, since the postsynaptic cell body had an initial voltage of -65 mV, and K⁻¹ channels are open, K⁻¹ ions would move out of the cell, moving the membrane potential towards the equilibrium potential for potassium, EK, which is -90 mV.

The new postsynaptic voltage would be a number more negative than the initial -65 mV but closer to EK = -90 mV. Therefore, the correct answer is B) between -70 mV and -90 mV because the postsynaptic membrane potential will become more hyperpolarized from its initial state but will not exceed the equilibrium potential for potassium.