Resting Membrane Potential: Videos & Practice Problems

Resting membrane potential refers to the voltage difference across the cell membrane when a neuron is not actively transmitting signals. This potential arises from the charge separation between the interior and exterior of the cell, typically measured at around -70 millivolts in the central nervous system (CNS). The range can vary from -40 to -90 millivolts depending on the specific type of neuron and its location in the body. At rest, the inside of the cell is more negatively charged compared to the outside.

The establishment of resting potential is primarily influenced by two key factors: the ionic composition of the intracellular and extracellular fluids, and the permeability of the plasma membrane to these ions. In a resting neuron, there is a higher concentration of sodium ions (Na⁺) outside the cell and a higher concentration of potassium ions (K⁺) inside. This difference in concentration creates a gradient that drives sodium into the cell and potassium out of the cell.

Importantly, neurons possess more potassium leak channels than sodium channels, which means the membrane is more permeable to potassium. As potassium ions leak out of the cell, they carry positive charge with them, contributing to the negative interior of the cell. While sodium ions also play a role, potassium is the primary contributor to resting potential.

The sodium-potassium pump (Na⁺/K⁺ ATPase) is crucial for maintaining these concentration gradients. It actively transports three sodium ions out of the cell and two potassium ions into the cell, ensuring that sodium remains more concentrated outside and potassium inside. This pump stabilizes the resting potential by counteracting the natural tendency of ions to diffuse down their concentration gradients.

Despite the presence of positively charged potassium ions inside the cell, the overall negative charge is maintained due to the presence of negatively charged proteins and other ions within the cytosol. The balance of ion concentrations and membrane permeability is essential for the neuron to remain at its resting potential, which is often described as a "Goldilocks zone"—not too much potassium leaking out, not too much sodium leaking in, but just right to facilitate proper neuronal function.

Understanding these dynamics is vital for grasping how neurons communicate and respond to stimuli. If the sodium-potassium pump were to fail, the balance of ion concentrations would be disrupted, potentially leading to an excessively negative interior, which could impair neuronal signaling.

The sodium-potassium pump is a vital membrane protein that plays a crucial role in maintaining the resting potential of neurons. It operates by actively transporting ions across the cell membrane, specifically ejecting three sodium ions (Na⁺) out of the cell while bringing in two potassium ions (K⁺). This process is essential for stabilizing the resting membrane potential rather than creating it. The resting potential is the electrical charge difference across the membrane when the neuron is not actively firing, typically around -70 mV.

It's important to note that the sodium-potassium pump does not allow negatively charged ions into the cell; instead, it primarily deals with the positively charged sodium and potassium ions. By maintaining the concentration gradients of these ions, the pump ensures that the inside of the neuron remains more negatively charged compared to the outside, which is critical for the generation of action potentials during neuronal signaling.

In summary, the sodium-potassium pump stabilizes the resting potential in neurons by regulating the concentrations of sodium and potassium ions, thus playing a fundamental role in the overall excitability of the neuron.