Membrane potential

Definition

Membrane potential refers to the electrical charge difference across a cell membrane, resulting from the unequal distribution of ions inside and outside the cell. This potential is crucial for various cellular processes, including the transmission of nerve impulses and muscle contraction. The membrane potential is largely influenced by ion channels and transporters, which control the movement of ions like sodium, potassium, calcium, and chloride across the cell membrane.

5 Must Know Facts For Your Next Test

1. Membrane potential is primarily generated by the movement of ions through selectively permeable membranes, with potassium ions (K+) being most influential at rest.
2. The sodium-potassium pump (Na+/K+ ATPase) actively transports sodium out of and potassium into the cell, helping to maintain the resting membrane potential.
3. Changes in membrane potential are critical for the function of excitable cells like neurons and muscle cells, enabling communication and contraction.
4. The equilibrium potential for each ion can be calculated using the Nernst equation, which considers the concentration gradient of that ion across the membrane.
5. During an action potential, rapid depolarization occurs as sodium channels open, followed by repolarization when potassium channels open to restore the resting membrane potential.

Review Questions

• How does the resting membrane potential contribute to the overall function of a neuron?
  • The resting membrane potential is essential for a neuron's ability to transmit signals. It creates a baseline negative charge inside the neuron that is crucial for depolarization during action potentials. When a stimulus occurs, this resting potential allows for a quick influx of sodium ions, which leads to a change in membrane potential necessary for signal propagation along the axon. Without an established resting membrane potential, neurons would struggle to generate action potentials effectively.
• Discuss the role of ion channels in generating and altering membrane potential during an action potential.
  • Ion channels play a pivotal role in both generating and altering membrane potential. Initially, at resting potential, potassium channels allow K+ to flow out, maintaining a negative charge inside. Upon receiving a stimulus, voltage-gated sodium channels open, causing Na+ to rush into the cell and depolarize the membrane. This rapid change leads to an action potential. Following this phase, potassium channels open again to repolarize the cell, returning it to its resting state. Thus, ion channels facilitate both the establishment and fluctuations of membrane potential.
• Evaluate how disturbances in membrane potential can affect cellular communication and overall physiology.
  • Disturbances in membrane potential can severely impact cellular communication and overall physiology. For instance, if there is an imbalance in ion concentrations due to malfunctioning ion channels or pumps, it may lead to inappropriate depolarization or hyperpolarization of cells. This disruption can affect nerve signal transmission and muscle contraction, potentially causing conditions like arrhythmias or paralysis. In essence, maintaining proper membrane potential is vital for normal physiological functions across different cell types.

Related terms

resting potential: The resting potential is the stable, negative charge maintained by a cell when it is not actively sending signals, typically around -70 mV in neurons.

action potential: An action potential is a rapid change in membrane potential that occurs when a neuron sends a signal down its axon, characterized by a brief depolarization followed by repolarization.

ion channel: Ion channels are protein structures in the cell membrane that allow specific ions to pass in and out of the cell, playing a key role in establishing and changing membrane potential.