Membrane potential

Definition

Membrane potential is the electrical potential difference across a cell's plasma membrane, resulting from the distribution of ions inside and outside the cell. This potential is crucial for various cellular functions, including nerve impulse transmission and muscle contraction. It arises from selective permeability of the membrane to ions, active transport mechanisms, and the overall ionic composition of the cytoplasm and extracellular fluid.

5 Must Know Facts For Your Next Test

1. Membrane potential is primarily determined by the concentration gradients of ions such as sodium (Na+), potassium (K+), chloride (Cl-), and calcium (Ca2+).
2. The sodium-potassium pump actively transports 3 Na+ ions out of the cell and 2 K+ ions into the cell, helping to maintain the resting membrane potential.
3. Changes in membrane potential can trigger action potentials, which are essential for communication between neurons.
4. During depolarization, sodium channels open, allowing Na+ ions to rush into the cell, making the inside more positive.
5. The process of repolarization restores the membrane potential back to its resting state after an action potential, primarily through the opening of potassium channels.

Review Questions

• How does the distribution of ions contribute to establishing and maintaining membrane potential?
  • The distribution of ions across the plasma membrane is key to establishing and maintaining membrane potential. The cell typically has a higher concentration of potassium (K+) ions inside and sodium (Na+) ions outside. This difference creates a negative charge inside the cell. The selective permeability of the membrane allows K+ to move out more easily than Na+ moves in, resulting in a negative resting potential. Active transport by ion pumps further helps maintain these gradients.
• What role do ion channels play in changes to membrane potential during action potentials?
  • Ion channels are vital for changes in membrane potential during action potentials. When a neuron is stimulated, voltage-gated sodium channels open, allowing Na+ ions to flood into the cell, leading to depolarization. Following this, voltage-gated potassium channels open, permitting K+ ions to exit the cell, which causes repolarization. This coordinated opening and closing of ion channels generates the rapid changes in membrane potential necessary for nerve signal transmission.
• Evaluate how active transport mechanisms influence membrane potential in excitable cells like neurons.
  • Active transport mechanisms, especially the sodium-potassium pump, critically influence membrane potential in excitable cells like neurons. By continually pumping 3 Na+ ions out of the cell and 2 K+ ions into it, this pump creates and maintains concentration gradients essential for resting membrane potential. Without this active transport, the ion balance would deteriorate, impairing action potentials and overall cellular communication. Thus, active transport not only establishes a negative resting potential but also prepares neurons for rapid depolarization during signaling.

Related terms

Resting potential: The membrane potential of a neuron at rest, typically around -70 mV, where the inside of the cell is more negatively charged compared to the outside.

Action potential: A rapid change in membrane potential that occurs when a neuron sends an impulse along its axon, characterized by depolarization followed by repolarization.

Ion channels: Protein structures embedded in the membrane that allow specific ions to pass through, playing a key role in establishing and changing membrane potential.