Define Resting Potential
Resting potential definition is that, it is the imbalance of electrical charge that persists between the interior of electrically excitable neurons a.k.a nerve cells, and their surroundings. The resting membrane potential value or a typical value of resting membrane potential is from − 60 to − 95 millivolts, where 1 millivolt = 0.001 volts, and the inside of the cell remains negatively charged.
In this article, we will discuss the resting potential of a neuron, resting potential and action potential, and the typical value of resting membrane potential.
Resting Membrane Potential
For our nervous system to function well, neurons must be able to send and receive electrical signals. These signals are possible because each neuron has a charged cellular membrane, i.e., a voltage or the potential difference between the inside and the outside, and the charge of this membrane can generate variations in response to neurotransmitter molecules released from other neurons and environmental or surrounding stimuli. To understand how neurons communicate or function, we must first understand the baseline of “resting” membrane charge.
Resting Membrane Potential of A Neuron
A neuron remains negatively charged at the rest state. The inside of a cell is approximately 70 millivolts or - 70 mV (This typical value of resting membrane potential is called the resting membrane potential) more negative than the outside (Please note that at resting stage nerve cell has the number varies by neuron type and by species). Resting membrane potential definition says that the resting membrane potential occurs because of the differences between the concentrations of ions inside and outside the cell.
Let’s suppose that the membrane was equally permeable to all ions, if each type of ion would have flown across the membrane, then the system would reach the equilibrium stage. Since ions cannot cross the membrane at their will because there are different concentrations of various ions inside and outside the cell. Generally, the difference in the number of positively charged potassium ions, i.e., K+ ions inside and outside the cell controls the resting membrane potential.
How is Resting Membrane Potential Maintained?
At resting stage nerve cell has accumulated K+ ions that reside inside the cell because of the net movement with the concentration gradient. The negative resting membrane potential is maintained by raising the concentration level of cations outside the cell, i.e., in the extracellular fluid relative to inside the cell, i.e., the cytoplasm.
Resting Potential And Action Potential
A cell membrane creates a negative charge within the cell. The cell membrane is more permeable to potassium ion movement than the movement of sodium ions. In neurons, K+ ions are maintained at higher concentrations within the cell; however, outside the cell, Na+ ions are present at higher-level concentrations. The cell possesses potassium and sodium leakage channels that allow the two cations to release their concentration gradient.
Typically, the neurons have more potassium leakage channels than sodium ones. Therefore, potassium diffuses out of the cell at a pace than the sodium leaks in. Because more cations leave the cell than entering into it; this, in turn, results in the interior of the cell being negatively charged relative to the outside of the cell.
The process of resting and action potential discussed above explains the action of the sodium-potassium pump that helps to maintain the resting potential, once established.
Action Potential
In the field of physiology, an action potential or AP occurs when the membrane potential of a specific cell at a particular location rises and falls with turbulence; this depolarization then causes adjacent cells to depolarize in the same manner. Action potentials take place in animal cells, or simply, excitable cells that include neurons, endocrine cells, muscle cells, and plant cells as well.
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Point to Note:
The relatively static or resting membrane potential is the ground value for trans-membrane voltage. The relatively static a.k.a resting potential or simply the resting voltage of quiescent cells is called the resting membrane potential. A resting membrane potential opposes the specific dynamic electrochemical phenomena in neurons. It is known as the action potential and graded membrane potential.
If the inside of a cell becomes electronegative (i.e., if the potential difference or the voltage reaches a level higher than that of the resting potential), then the membrane or the cell becomes hyperpolarized.
However, when the inside of the cell becomes less negative (i.e., the potential reaches below the resting potential value), the process is depolarization.
FAQs on Resting Potential
1. What exactly is meant by resting potential in simple terms?
In simple terms, the resting potential is the electrical charge difference across the cell membrane of a neuron when it is not actively sending a signal. Think of it as a tiny, charged battery that is 'at rest' but ready to fire. The inside of the neuron is negatively charged compared to the outside during this state.
2. How does a neuron maintain its resting potential?
A neuron maintains its resting potential primarily through two mechanisms:
- The Sodium-Potassium Pump: This pump uses energy to actively push three positive sodium ions (Na+) out of the cell for every two positive potassium ions (K+) it brings in. This creates an electrical imbalance.
- Potassium Leak Channels: The cell membrane has channels that allow potassium ions to 'leak' out of the cell more easily than sodium ions can leak in. This outward flow of positive charge makes the inside of the cell more negative.
3. What are the key characteristics of a neuron at resting potential?
A neuron in its resting state has three main characteristics:
- The inside of the cell membrane is negatively charged relative to the outside.
- The membrane is said to be polarized because of this charge difference.
- There is a higher concentration of potassium ions (K+) inside the neuron and a higher concentration of sodium ions (Na+) outside the neuron.
4. Why is the resting potential a negative value, like -70mV?
The resting potential is negative mainly because more positive ions are leaving the cell than entering it. The two biggest contributors are the constant leaking out of positive potassium ions (K+) down their concentration gradient and the presence of large, negatively charged proteins trapped inside the neuron. The sodium-potassium pump also helps by pumping out more positive ions (3 Na+) than it pumps in (2 K+).
5. What is the main difference between resting potential and action potential?
The main difference is their state of activity. Resting potential is the neuron's default, inactive state where the inside is negative. An action potential is a brief, active event where the neuron fires a signal. During an action potential, there is a rapid and temporary reversal of charge, making the inside of the neuron become positively charged.
6. I've seen resting potential listed as -70mV and -90mV. Which one is correct?
Both can be correct, as the exact value varies. For a typical neuron, -70 millivolts (mV) is the most commonly cited value and is used as a standard example in many textbooks. However, the resting potential can range from -60mV to -90mV depending on the specific type of neuron or cell. For example, cardiac muscle cells often have a resting potential closer to -90mV.
7. What is the specific job of the sodium-potassium pump in this process?
The sodium-potassium pump's specific job is to create and maintain the steep ion concentration gradients needed for the resting potential. It uses energy (ATP) to perform active transport, moving Na+ and K+ ions against their natural tendency to diffuse. Without this pump constantly working, the ion concentrations would eventually balance out, and the resting potential would disappear.
