BiologyChapter 5: Nervous System of Man
5.5.2 Resting Membrane Potential
Resting Membrane Potential (RMP):
Explanation level
The resting membrane potential is the electrical potential difference across the neuron membrane when the neuron is at rest. It is characterized by a more positive outer surface and a more negative inner surface. This state is also called the polarized state.
Definition
Resting Membrane Potential (RMP): The resting membrane potential is the electrical potential difference across the neuron membrane when the neuron is not being stimulated or conducting impulses. It is characterized by a more positive outer surface of the neuron membrane than the inner surface. This state is also referred to as the polarized state. The resting membrane potential is expressed as −70 mV.
Main Idea
- The resting membrane potential is the electrical potential difference across the neuron membrane at rest.
- It is characterized by a more positive outer surface and a more negative inner surface.
- This state is called the polarized state.
- The neuron is supposed to be at rest.
- There is an unequal distribution of ions on the two sides of the nerve cell membrane.
- The resting membrane potential is expressed as −70 mV.
- The minus sign indicates that the inside is negative relative to the outside.
- It occurs when a membrane is not being stimulated or conducting impulses.
Core Concept
- Resting Membrane Potential (RMP) = electrical potential at rest
- Polarized state = more positive outside; more negative inside
- **Value** = −70 mV
- Factors = distribution and active movement of Na⁺ and K⁺ ions; negative organic ions; leakage of K⁺ ions
- **Na⁺/K⁺ pump** = 3 Na⁺ out; 2 K⁺ in
- K⁺ concentration = 30 times greater inside
- Na⁺ concentration = nearly 10 times greater outside
- Negative organic ions = amino acids, proteins, RNA
- K⁺ leakage = through leaky K⁺ gates
Detailed Explanation
Resting Membrane Potential
- It is characterized by more positive outer surface of neuron membrane than inner surface.
- This state is also referred as polarized state and the neuron is supposed to be at rest.
- This means that there is an unequal distribution of ions on the two sides of the nerve cell membrane.
- This potential generally measures about 70 mV (with the inside of the membrane negative with respect to the outside).
- So, the resting membrane potential is expressed as −70 mV.
- The minus sign indicates that the inside is negative relative to (or compared to) the outside.
- It is called a resting membrane potential because it occurs when a membrane is not being stimulated or conducting impulses.
Factors Establishing Resting Membrane Potential
Resting membrane potential is established by the following factors:
1. Distribution and Active Movement of Na⁺ and K⁺ Ions
- The concentration of potassium (K⁺) is 30 times greater in the fluid inside the neuron cell than outside.
- The concentration of sodium ions (Na⁺) is nearly 10 times greater in the fluid outside the cell than inside.
- These ions are continuously moved against their concentration gradient through sodium-potassium pumps by the expenditure of energy.
- For every two K⁺ that are actively transported inward, three Na⁺ are pumped out.
- So inside becomes more negative than outside of the neuron membrane.
2. Negative Organic Ions
- There are many types of organic compounds in the neuron cytoplasm that also have negative charges.
- These ions include some amino acids, many proteins and RNA.
- Presence of these ions in the neuron cytoplasm makes inside of neuron more negative than outside.
3. Leakage of K⁺ Ions
- Cell membrane of neuron also has many channel proteins called gates.
- K⁺ ions leak continuously through leaky K⁺ gates.
- This also makes more positive outside of neuron than inside.
Overall Result
- Overall there are more positive charges on the outside than on the inside.
- This is known as resting membrane potential.
- This potential will be maintained until the membrane is disturbed or stimulated by a sufficiently strong stimulus (threshold), then action potential will be produced.
Summary Table of Factors
| Factor | Description | Effect |
|---|---|---|
| Na⁺/K⁺ distribution | K⁺ 30× greater inside; Na⁺ 10× greater outside | Inside more negative |
| Na⁺/K⁺ pump | 3 Na⁺ out; 2 K⁺ in | Inside more negative |
| Negative organic ions | Amino acids, proteins, RNA inside | Inside more negative |
| K⁺ leakage | K⁺ leaks out through leaky K⁺ gates | Outside more positive |
Summary of Resting Membrane Potential
| Feature | Description |
|---|---|
| State | Polarized |
| Inside | Negative |
| Outside | Positive |
| Value | −70 mV |
| Factors | Na⁺/K⁺ distribution; negative organic ions; K⁺ leakage |
| Na⁺/K⁺ pump | 3 Na⁺ out; 2 K⁺ in |
| K⁺ concentration | 30 times greater inside |
| Na⁺ concentration | Nearly 10 times greater outside |
Intermediate Level
Resting Membrane Potential
| Feature | Description |
|---|---|
| State | Polarized |
| Inside | Negative |
| Outside | Positive |
| Value | −70 mV |
| Definition | Electrical potential at rest |
Factors Establishing Resting Membrane Potential
| Factor | Description | Effect |
|---|---|---|
| Na⁺/K⁺ distribution | K⁺ 30× greater inside; Na⁺ 10× greater outside | Inside more negative |
| Na⁺/K⁺ pump | 3 Na⁺ out; 2 K⁺ in | Inside more negative |
| Negative organic ions | Amino acids, proteins, RNA inside | Inside more negative |
| K⁺ leakage | K⁺ leaks out through leaky K⁺ gates | Outside more positive |
Sodium-Potassium Pump
| Feature | Description |
|---|---|
| Function | Moves ions against concentration gradient |
| Energy | Expenditure of energy (ATP) |
| Ratio | 3 Na⁺ out; 2 K⁺ in |
| Effect | Inside more negative |
Ion Concentrations
| Ion | Inside | Outside |
|---|---|---|
| K⁺ | 30 times greater | Lower |
| Na⁺ | Lower | 10 times greater |
Negative Organic Ions
| Ion | Location | Effect |
|---|---|---|
| Amino acids | Inside | Inside more negative |
| Proteins | Inside | Inside more negative |
| RNA | Inside | Inside more negative |
K⁺ Leakage
| Feature | Description |
|---|---|
| Gates | Leaky K⁺ gates |
| Movement | K⁺ leaks out |
| Effect | Outside more positive |
Formula / Mathematical Form
Not applicable to this topic.
Solved Example
Not applicable to this topic (descriptive topic).
Important Points
- 1. Resting membrane potential is the electrical potential at rest.
- 2. It is characterized by more positive outside and more negative inside.
- 3. It is called the polarized state.
- 4. The neuron is supposed to be at rest.
- 5. There is an unequal distribution of ions.
- 6. The potential is expressed as −70 mV.
- 7. The minus sign indicates the inside is negative relative to the outside.
- 8. It occurs when the membrane is not being stimulated.
- 9. K⁺ concentration is 30 times greater inside.
- 10. Na⁺ concentration is nearly 10 times greater outside.
- 11. Sodium-potassium pumps move ions against concentration gradient.
- 12. For every 2 K⁺ transported inward, 3 Na⁺ are pumped out.
- 13. Negative organic ions include amino acids, proteins, and RNA.
- 14. K⁺ ions leak through leaky K⁺ gates.
- 15. Overall, more positive charges are on the outside.
- 16. The potential is maintained until a threshold stimulus is applied.
- 17. Then action potential is produced.
- 18. The resting membrane potential is essential for nerve impulse generation.
- 19. It prepares the neuron for depolarization.
- 20. Without it, nerve impulses could not be generated.
Remember
- - Resting Membrane Potential (RMP) = electrical potential at rest
- - Polarized state = more positive outside; more negative inside
- - **Value** = −70 mV
- - Factors = Na⁺/K⁺ distribution; negative organic ions; K⁺ leakage
- - **Na⁺/K⁺ pump** = 3 Na⁺ out; 2 K⁺ in
- - K⁺ concentration = 30 times greater inside
- - Na⁺ concentration = nearly 10 times greater outside
- - Negative organic ions = amino acids, proteins, RNA
- - K⁺ leakage = through leaky K⁺ gates
- - Maintained until = threshold stimulus
- - Then = action potential produced
Common Mistakes
- 1. Thinking the inside is positive at rest — Inside is negative at rest.
- 2. Confusing resting and active membrane potential — RMP = polarized; AMP = depolarized.
- 3. **Mixing up the values** — RMP = −70 mV.
- 4. Forgetting the role of the sodium-potassium pump — It maintains the resting potential.
- 5. Mixing up the ion concentrations — K⁺ is higher inside; Na⁺ is higher outside.
- 6. Forgetting the role of negative organic ions — They make the inside more negative.
- 7. Ignoring K⁺ leakage — K⁺ leakage makes the outside more positive.
- 8. Thinking the potential is constant — It changes when the neuron is stimulated.
- 9. Believing the neuron is always at rest — Neurons can be stimulated.
- 10. Confusing the sodium-potassium pump ratio — 3 Na⁺ out; 2 K⁺ in.
Quick Revision
The resting membrane potential is the electrical potential difference across the neuron membrane when the neuron is not being stimulated or conducting impulses. It is characterized by a more positive outer surface of the neuron membrane than the inner surface. This state is also referred to as the polarized state, and the neuron is supposed to be at rest. This means that there is an unequal distribution of ions on the two sides of the nerve cell membrane. This potential generally measures about 70 mV (with the inside of the membrane negative with respect to the outside). So, the resting membrane potential is expressed as −70 mV. The minus sign indicates that the inside is negative relative to the outside. Resting membrane potential is established by the distribution and active movement of Na⁺ and K⁺ ions, the presence of negative organic ions, and the leakage of K⁺ ions. The sodium-potassium pump moves 3 Na⁺ out and 2 K⁺ in. K⁺ concentration is 30 times greater inside, and Na⁺ concentration is nearly 10 times greater outside. Negative organic ions include amino acids, proteins, and RNA. K⁺ ions leak through leaky K⁺ gates. Overall, there are more positive charges on the outside than on the inside. This potential is maintained until the membrane is disturbed or stimulated by a sufficiently strong stimulus (threshold), then action potential will be produced.
60-Second Revision
- Resting Membrane Potential (RMP) = electrical potential at rest
- Polarized state = more positive outside; more negative inside
- Value = −70 mV
- Factors = Na⁺/K⁺ distribution; negative organic ions; K⁺ leakage
- Na⁺/K⁺ pump = 3 Na⁺ out; 2 K⁺ in
- K⁺ concentration = 30 times greater inside
- Na⁺ concentration = nearly 10 times greater outside
- Negative organic ions = amino acids, proteins, RNA
- K⁺ leakage = through leaky K⁺ gates
- Warning: Inside is negative at rest; outside is positive
NEXT TOPIC
- Chapter:
- 5. Nervous System of Man
- Topic:
- 5.5.3 ACTIVE MEMBRANE POTENTIAL
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Review the key facts, formulas and checks before you move on.5.5.2 Resting Membrane Potential
Sticky Notes · Quick Revision
Key Point 1
- Resting Membrane Potential (RMP) = electrical potential at rest
Key Point 2
- Polarized state = more positive outside; more negative inside
Key Point 3
- Value = −70 mV
Key Point 4
- Factors = Na⁺/K⁺ distribution; negative organic ions; K⁺ leakage
Key Point 5
- Na⁺/K⁺ pump = 3 Na⁺ out; 2 K⁺ in
Key Point 6
- K⁺ concentration = 30 times greater inside
Key Point 7
- Na⁺ concentration = nearly 10 times greater outside
Key Point 8
- Negative organic ions = amino acids, proteins, RNA
Key Point 9
- K⁺ leakage = through leaky K⁺ gates
Key Point 10
- Maintained until = threshold stimulus
Key Point 11
- Then = action potential produced
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