A change in the axon membrane potential from -70 mV to -90 mV would be termed a(n) _____

Question

BlackTom AI · Accepted Answer

To tackle this question, I’ll lay out each option and examine what it means in the context of neuronal membrane potential changes.
Option 1: 'depolarization.' A depolarization event occurs when the membrane potential becomes less negative (for example from -70 mV toward 0 mV). Since the change described moves from -70 mV to -90 mV, the inside of the cell becomes more negative, which is the opposite of depolarization. Therefore, this option is incorrect.
Option 2: 'threshold potential.' The threshold potential refers to the critical level that the membrane potential must reach to trigger an action potential, not to a type of change in membrane potential itself. The described shift to -90 mV is a hyperpolarizing change, not a threshold crossing event. Hence, this option is incorrect.
Option 3: 'action potential.' An action potential is a rapid, transient reversal of membrane potential (depolarization) followed by repolarization, typically moving from around -70 mV to positive values and back. The given change to -90 mV is a steady, hyperpolarizing shift, not an action potential. Thus, this option is incorrect.
Option 4: 'hyperpolarization.' Hyperpolarization means the membrane potential becomes more negative than the resting potential (e.g., moving from -70 mV to -90 mV). This exactly matches the described change, making this the correct characterization of the event.
Option 5: 'excitatory local potential.' An excitatory local potential (excitatory postsynaptic potential, EPSP) typically brings the membrane potential closer to the threshold by depolarizing (making it less negative), not by hyperpolarizing. Therefore, this option is incorrect.
Summarizing the reasoning: depolarization would make the cell less negative, which is not what's described here; the threshold potential is about readiness to fire, not a descriptive change; an action potential is a rapid spike rather than a steady hyperpolarizing shift; hyperpolarization precisely describes the shift to a more negative potential; excitatory local potentials drive depolarization, not hyperpolarization. Therefore, hyperpolarization is the appropriate term for a shift from -70 mV to -90 mV.

PSYC304 Quiz 4

A change in the axon membrane potential from -70 mV to -90 mV would be termed a(n) _____

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