Question

A presynaptic nerve terminal releases a neurotransmitter that increases Cl ‐ conductance in the postsynaptic membrane. If the postsynaptic cell body had an initial voltage of ‐65 mV and E Na = +50 mV, ECl = ‐65 mV and EK = ‐90 mV, the new postsynaptic voltage will be:

A) between —65 mV and —90 mV.
B) between —65 mV and +50 mV.
C) —65 mV.
D) more negative than —90 mV.
E) more positive than +50 mV.

Answer 1

The new postsynaptic voltage remains unchanged at -65 mV because increasing Cl- conductance will not alter the membrane potential when the Cl- equilibrium potential matches the initial voltage of the neuron.

Step-by-step explanation:

The question is about how the voltage of the postsynaptic neuron changes in response to an increase in Cl- conductance. The neuron's initial voltage is -65 mV, and the equilibrium potentials for Na+, Cl-, and K+ are given as +50 mV, -65 mV, and -90 mV, respectively. When the neurotransmitter binds to the postsynaptic receptors and increases Cl- conductance, Cl- ions will flow into the neuron to try to reach the equilibrium potential for Cl-, which is the same as the initial voltage of the postsynaptic neuron. Therefore, the new postsynaptic voltage will remain C) -65 mV, since increasing Cl- conductance will not change the membrane potential if the Cl- equilibrium potential is the same as the initial membrane potential.