16.13
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…
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.
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Q1: What is the resting membrane potential and why is it important?
The resting membrane potential is the electrical voltage across a neuron's membrane at rest, typically around -70 millivolts. This negative charge is essential for neuronal function because it provides the electrical foundation for generating signals and responding to stimuli. Without this potential difference, neurons cannot produce action potentials or communicate with other cells.
Q2: How does the sodium-potassium pump maintain the resting membrane potential?
The sodium-potassium pump actively transports three sodium ions out of the cell and two potassium ions into the cell, using ATP energy. This unequal exchange creates and maintains ion concentration gradients across the membrane. The pump's continuous activity sustains the negative resting potential by keeping more positive ions outside the cell than inside.
Q3: What role does the electrochemical gradient play in establishing resting potential?
The electrochemical gradient and channel proteins work together to establish resting potential by creating both chemical and electrical driving forces for ions. Potassium ions leak out through open channels down their concentration gradient, making the interior more negative. This ion movement continues until the electrical gradient balances the chemical gradient, stabilizing the resting membrane potential.
Q4: Why is potassium more permeable than sodium at rest?
At rest, the neuronal membrane is more permeable to potassium than sodium because more potassium channels remain open while sodium channels are mostly closed. This selective permeability allows potassium to leak out of the cell, driving the membrane potential toward the potassium equilibrium potential. The differential permeability is crucial for maintaining the negative resting potential.
Q5: How does the resting membrane potential relate to action potential generation?
The resting membrane potential provides the starting point for action potential generation. When a neuron receives sufficient stimulation, the membrane potential depolarizes from its resting state of approximately -70 millivolts. This change triggers the opening of voltage-gated sodium channels, initiating the rapid depolarization phase of the action potential phases of stimulation.
Q6: What happens to the resting membrane potential if ion pumps fail?
If sodium-potassium pumps fail, ion gradients gradually dissipate and the resting membrane potential becomes less negative. Without active transport maintaining concentration differences, sodium accumulates inside the cell and potassium leaks out. Eventually, the membrane potential approaches zero, preventing neurons from generating action potentials and disrupting normal nervous system function.
Q7: How do ion channels contribute to maintaining resting potential stability?
Ion channels maintain resting potential stability through selective permeability and leak conductance. Open potassium channels allow continuous potassium efflux, while closed sodium channels prevent sodium influx. This balanced ion leakage, combined with active pumping, creates a steady-state equilibrium where the resting membrane potential remains stable at approximately -70 millivolts.