Transcript

0:00 – 0:30  The resting membrane potential is the voltage across the neuronal cell membrane that occurs when a neuron is not actively signaling, or being excited, or being inhibited.  A typical value for the resting membrane potential is approximately -70mV, but this varies among cell types.  The exact value of the resting membrane potential is determined by ionic concentration differences between the intracellular and extracellular environments, and by the ionic permeability of the neuronal cell membrane.

0:30-2:30

There are two ‘driving forces’ that control the movement of ions and set the resting membrane potential. The first is a chemical driving force, where ions diffuse down their concentration gradient through leak channels. In this case there are leak channels permeable to sodium and chloride, and so the two ions evenly distribute in each compartment.

The second driving force is electrical. Ions are charged and so cations like sodium are repelled by the negative terminal or anode, and attracted to the positive terminal or cathode. The opposite is true for anions like chloride. Ion movement, or current, is always described in the direction of the accumulation of positive charge, so it is flowing to the right in both cases.

Concentration gradients are generated and maintained using the sodium-potassium pump, with 3 sodium ions moved out for every two potassium ions moved in. The requires energy in the form of ATP, since ions are pumped against their gradients, with sodium higher outside the neuron and potassium higher inside.

Higher concentrations of potassium inside create a chemical driving force and so potassium ions diffuse through potassium leak channels. As more positively charged potassium leaves the neuron, it accumulates along the membrane creating an electrical driving force, which counteracts the chemical driving force. This creates an ‘equilibrium potential’, which is a transmembrane voltage that prevents ions from moving down their concentration gradient.

Equilibrium potentials for individual ions can be calculated using the Nernst Equation, given the charge of the ion, or Z, and the concentrations of the ion inside and outside the neuron. Sodium, potassium, calcium and chloride are the major ions involved in changing transmembrane voltage and each has a different equilibrium potential.

Leak channels in the neuronal membrane are selectively permeable to potassium. This is why the resting potential is negative and closer to potassium’s equilibrium potential. However, it is slightly more positive than potassium, around – 65 mV. This is because there is also a small permeability to sodium, which has a very positive equilibrium potential. To calculate equilibrium potentials comprised of multiple ions, like the resting potential, we use the Goldman equation, which also takes into account relative ion permeabilities.

2:30-3:00 [Parallel Vocabulary] In introductory classes you learned about the resting membrane potential. But Neuroscience is an interdisciplinary field, so there are many words for this term – For example, it may be shortened to resting potential, or just rest. Rather than “potential”, you may hear the terms electrical potential difference, potential difference, or voltage. So….“resting potential”, “voltage at rest”, and “electrical potential difference at rest” may all refer to the same thing.

3:00-4:00 [Here’s a real world example] The resting membrane potential is important in almost every aspect of intercellular neural communication including action potential signaling, synaptic transmission, and synaptic plasticity. For example, did you know that kidney failure can produce hyperkalemia, a potentially lethal condition that arises when the body fails to produce urine and the blood concentration of potassium increases. A typical case of hyperkalemia increases the blood concentration of potassium by more than 25%. We can use the Goldman equation to predict the effect of hyperkalemia. Recall that the Goldman equation uses ionic permeabilities and concentration differences to compute the membrane voltage. Increased potassium in the extracellular environment leads to an increase in the resting membrane potential – this depolarization can impair electrical signaling in cells of the brain and heart.

4:00-6:00 [Follow along with this example]

6:00-6:30 [Here are a few readings to help you review]
1) Neuroscience Exploring the Brain (Bear)

• Chapter 3: “The Neuronal Membrane at Rest”.

2) Principles of Human Physiology (Stanfield)

• Chapter 7: “Nerve Cells and Electrical Signaling”

Media Attributions

Sodium-Potassium pump by CNX OpenStax, is licensed under a Creative Commons Attribution International License (CC BY 4.0), via Wikimedia Commons

Membrane at Rest’ by Casey Henley is licensed under a Creative Commons Attribution Non-Commercial Share-Alike (CC BY-NC-SA) 4.0 International License