Rucete ✏ Campbell Biology In a Nutshell
Unit 7 ANIMAL FORM AND FUNCTION — Concept 48.2 Ion Pumps and Ion Channels Establish the Resting Potential of a Neuron
Neurons maintain a resting membrane potential—an electrical voltage across their membrane—through the unequal distribution of ions, primarily potassium and sodium. This potential is critical for nerve signaling and depends on selective ion permeability and active transport.
1. Membrane Potential Basics
- Membrane potential: voltage difference across a cell’s membrane
- Resting potential: –60 to –80 mV; inside of neuron is negatively charged
2. Sodium-Potassium Pump
- Uses ATP to pump 3 Na⁺ out and 2 K⁺ in
- Creates high K⁺ inside and high Na⁺ outside
- Contributes indirectly to membrane potential
3. Role of Ion Channels
- Ion channels allow passive ion flow
- Leak K⁺ channels let K⁺ exit, making inside more negative
- Negative charge buildup halts further K⁺ outflow → electrochemical equilibrium
4. Equilibrium Potentials
- Equilibrium potential (Eₖ): no net ion flow
- Calculated with the Nernst equation
- Eₖ ≈ –90 mV; Eₙₐ ≈ +62 mV; resting potential is closer to Eₖ
5. Steady State Currents
- At rest: K⁺ leaks out, Na⁺ leaks in — balanced by the Na⁺/K⁺ pump
- Resting potential remains stable over time
6. Gated Ion Channels and Stimulus Response
- Gated channels open/close with voltage or chemical signals
- Voltage-gated Na⁺ channels → depolarization (less negative)
- Voltage-gated K⁺ channels → hyperpolarization (more negative)
- These changes underlie action potentials (discussed next)
In a Nutshell
The resting potential in neurons arises from ion gradients maintained by the sodium-potassium pump and selective permeability through leak channels, especially for potassium. This electrical potential prepares neurons to rapidly respond to stimuli via changes in ion flow—enabling communication throughout the nervous system.