Name: how neurons keep a negative voltage
Uploaded: 2023-04-30T10:11:09.000Z
Duration: 1 min 24 s
Channel: JoVE

The resting membrane potential is the difference in electrical potential between the inside and outside of the cell membrane of neurons at rest when they are not being stimulated. Typically, the value is around negative 70 millivolts, meaning that it is more negative inside.
Cell membranes are selectively permeable because most ions and molecules cannot passively diffuse across them. They often require transmembrane proteins, such as ion channels, to allow them to pass through. When a neuron is at rest, potassium leak channels are the main type of ion channel that are open.
Another transmembrane protein, the sodium-potassium pump, uses energy to continuously move sodium out of the cell, and potassium in. This action creates a concentration gradient, with a higher concentration of potassium inside than outside.
The force of diffusion then causes potassium ions to move down their concentration gradient, through the open potassium leak channels, and out of the cell.
The movement of these positive ions out combined with negatively charged proteins inside the cell creates a negative charge inside the membrane, a negative potential when a neuron is at rest.

resting membrane potential

Resting Membrane Potential

The relative difference in electrical charge, or voltage, between the inside and the outside of a cell membrane, is called the membrane potential. It is generated by differences in permeability of the membrane to various ions and the concentrations of these ions across the membrane.
The Inside of a Neuron is More Negative
The membrane potential of a cell can be measured by inserting a microelectrode into a cell and comparing the charge to a reference electrode in the extracellular fluid. The membrane potential of a neuron at rest&#8212;that is, a neuron not currently receiving or sending messages&#8212;is negative, typically around -70 millivolts (mV). This is called the resting membrane potential. The negative value indicates that the inside of the membrane is relatively more negative than the outside&#8212;it is polarized. The resting potential results from two major factors: selective permeability of the membrane and differences in ion concentration inside the cell compared to outside.
Membrane Permeability
Cell membranes are selectively permeable because most ions and molecules cannot cross the lipid bilayer without help, often from ion channel proteins that span the membrane. This is because the charged ions cannot diffuse through the uncharged hydrophobic interior of membranes. The most common intra- and extracellular ions found in the nervous tissue are potassium (K+), sodium (Na+), chloride (Cl-), and calcium (Ca2+). When a neuron is at rest, potassium (K+) channels are the main type of ion channel that is open&#8212;allowing K+ to migrate across the membrane. This permeability, together with the large intracellular concentrations, make the neuron&#8217;s resting membrane potential determined mainly by the movement of K+.
Pumps Create Concentration Gradients
Differences in ion concentration between the inside and outside of neurons are primarily due to the activity of the sodium-potassium (Na+/K+) pump&#8212;a transmembrane protein that continuously pumps three Na+ ions out of the cell for every two K+ ions it pumps in. This establishes concentration gradients, with a higher concentration of Na+ ions outside of neurons and a higher concentration of K+ ions inside.
Since the membrane is primarily permeable to K+ at rest&#8212;due to the open K+ channels&#8212;K+ can diffuse down its concentration gradient to the region of lower concentration out of the cell. These positive charges leaving the cell, combined with the fact that there are many negatively charged proteins inside the cell, cause the inside to be relatively more negative.
Eventually, outward diffusion of K+ is balanced by the electrostatic repulsion of positive charges accumulating outside the cell, and electrochemical equilibrium is reached. The net effect is the observed negative resting potential. The resting potential is very important in the nervous system because changes in membrane potential&#8212;such as the action potential&#8212;are the basis for neural signaling.
Beware the Pufferfish
Pufferfish is not often found on many seafood menus outside of Japan, in part because they contain a potent neurotoxin. Tetrodotoxin (TTX) is a very selective voltage-gated sodium channel blocker that is lethal in minimal doses. The median lethal dose (LD50) for mice is 334 &#956;g/kg, compared to 8.5 mg/kg for potassium cyanide. It has also served as an essential tool in neuroscience research. The toxin blocks the flow of Na+ into the cell when the channel opens. It, therefore, disrupts action potentials&#8212;but not the resting membrane potential&#8212;and can be used to silence neuronal activity. Its mechanism of action was demonstrated by Toshio Narahashi and John W. Moore at Duke University, working on the giant lobster axon in 1964.

The relative difference in electrical charge, or voltage, between the inside and the outside of a cell membrane, is called the membrane potential. It is ...

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Channels and the Electrical Properties of Membranes

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KEY TERMS AND CONCEPTS

how neurons keep a negative voltage

Neurons keep a negative voltage across their membrane when they are at rest. This membrane potential is the voltage difference between the inside and outside of a cell. In a resting neuron, it is usually around -70 millivolts, which means the inside is more negative than the outside and the cell is polarized.

This negative charge depends on two main factors. The membrane is selectively permeable, so most ions and molecules cannot cross the lipid bilayer without help from ion channel proteins. The most common ions in nervous tissue are potassium (K+), sodium (Na+), chloride (Cl-), and calcium (Ca2+). When a neuron is resting, potassium channels are the main channels that stay open, so K+ can move across the membrane.

The sodium-potassium pump also helps set up the resting state. This transmembrane protein pumps three Na+ ions out of the cell for every two K+ ions it pumps in. That creates a higher Na+ concentration outside the neuron and a higher K+ concentration inside. Because the membrane is most permeable to K+ at rest, K+ diffuses out of the cell down its concentration gradient.

As positive K+ ions leave, the inside of the cell becomes relatively more negative. Negatively charged proteins inside the cell also add to this effect. Over time, outward movement of K+ is balanced by the electrical force that pulls positive charge back toward the cell. This electrochemical equilibrium produces the observed negative resting potential.

Membrane potential is measured by placing a microelectrode inside the cell and comparing it with a reference electrode in the extracellular fluid. Resting potential matters because changes in membrane potential, such as action potentials, are the basis of neural signaling. Tetrodotoxin, or TTX, from pufferfish blocks voltage-gated sodium channels. It stops Na+ from entering when those channels open, so it disrupts action potentials but not the resting membrane potential. TTX has also been an important tool in neuroscience research, including classic work on the giant lobster axon at Duke University.

How Neurons Keep a Negative Voltage

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Neurons keep a negative voltage across their membrane when they are at rest. This membrane potential is the voltage difference between the inside and outside of a cell. In a resting neuron, it is usually around -70 millivolts, which means the inside is more negative than the outside and the cell is polarized. This negative charge depends on two main factors. The membrane is selectively permeable, so most ions and molecules cannot cross the lipid bilayer without help from ion channel proteins.

resting potential decay

Resting Membrane Potential Maintenance

The resting membrane potential stays near -70 mV in a neuron because the membrane allows ions to move in a selective way. At rest, the membrane is slightly permeable to sodium ions (Na+) and chloride ions (Cl-) and highly permeable to potassium ions (K+). Ion channels and pumps keep the concentration differences between the inside and outside of the cell in place. Potassium leak channels let K+ move out of the cell at rest. This outward movement makes the inside of the cell more negative. A...

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the-role-of-ion-channels-in-neuronal-computation

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key terms and concepts

Learn how neurons maintain a negative resting voltage through ion channels, the sodium-potassium pump, and potassium movement across the membrane.

How Neurons Keep a Negative Voltage | JoVE K12

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How Neurons Keep a Negative Voltage

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