Understanding the Cellular Electrochemical Gradient: The Role and Importance of Membrane Potential

voltage difference between inside and outside of cell caused by separation of positively and negatively charged ions by semi-permeable cell membrane

resting membrane potential

Cells have an electrochemical gradient, which means there is a voltage difference between the inside and the outside of the cell. This voltage difference is caused by the separation of positively and negatively charged ions by the semi-permeable cell membrane.

The cell membrane has channels and pumps that regulate the movement of ions across the membrane. For example, the sodium-potassium pump will pump three sodium ions out of the cell for every two potassium ions that it pumps in. This creates a concentration gradient, but also an electrical gradient because the sodium ions are positively charged and the potassium ions are negatively charged.

In addition to ion pumps, the membrane also has ion channels that allow ions to move across the membrane. These channels are gated, meaning they can open and close in response to signals. For example, voltage-gated channels open in response to changes in membrane potential.

On the inside of the cell, there are many negatively charged proteins and other molecules. This creates an overall negative charge inside the cell. On the outside of the cell, there are more positively charged ions, such as sodium and calcium. This creates an overall positive charge outside the cell.

The voltage difference across the membrane is measured in millivolts and is called the membrane potential. In a typical animal cell, the membrane potential is around -70mV. This means that the inside of the cell is 70 millivolts more negative than the outside of the cell.

The membrane potential is important for many cellular functions, such as muscle contraction and nerve impulses. Changes in membrane potential can trigger ion channels to open or close, which can lead to a cascade of events inside the cell.

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