Video Transcript
What is a typical value for resting potential in human axons? (A) Negative 70 millivolts, (B) 65 millivolts, (C) zero millivolts, (D) 40
millivolts.
This question is asking us to recall what the resting potential is and the typical
value of it. When a neuron is at rest, that is, not transmitting information via a nerve impulse,
the membrane potential is maintained at the resting potential. To review, the membrane potential is the difference in ion charges between the inside
and outside of the neuron. So, the resting potential is the membrane potential when the neuron is at rest.
When a neuron is at rest, the resting potential is maintained by proteins called the
sodium–potassium pumps, which are found embedded in the membrane. These pumps move three sodium ions into the extracellular space while moving two
potassium ions into the intracellular space. To move the positively charged sodium and potassium ions against their concentration
gradients, the pump uses ATP energy.
The movement of ions across the membrane makes the voltage in the extracellular space
more positive than the neuron’s cytoplasm. The pump creates an imbalanced distribution of ions across the membrane. Potassium ions are more concentrated inside of the neuron, while sodium ions are
concentrated outside of the cell.
In addition to movement across the membrane by the sodium–potassium pump, potassium
passively diffuses out of the cell through leak channels which are always open. The movement of potassium ions unidirectionally through the leak channels contributes
to reducing the number of positive charges inside of the neuron.
When these actions combine, the intracellular space becomes more negatively charged
than the extracellular space, polarizing the membrane and giving the neuron a
resting potential of around negative 70 millivolts.
Now that we’ve looked at the movement of ions during the resting potential, we can
answer the question. The typical value for the resting potential in human axons is negative 70
millivolts.
