Depolarization: Definition & Concept

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  • 0:00 Cell-To-Cell Communication
  • 0:28 Depolarization At A Glance
  • 2:21 Excitable Cells
  • 3:01 Lesson Summary
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Lesson Transcript
Instructor: John Williams
Many cells use electrical stimulation to communicate with each other. This process starts with depolarization. The lesson looks at the role of depolarization in the electrical communication within and between cells.

Cell-To-Cell Communication

Cell-to-cell communication is a critical process in biological systems. In order for cells to work together, they must be able to coordinate activities for each function that they provide. This communication can come in many forms, but in some cells, this communication is electrically based. For those specific cells, the process of depolarization is key to this communication.

Depolarization at a Glance

Cells that can be stimulated electrically are said to be excitable. This means that if an electrical signal is applied or delivered to these cells, they'll respond by becoming functional. This process is driven by electrochemical gradients.

Electrochemical gradients are differences in ion concentration on the inside and outside of a cell. Generally speaking, if a cell membrane has more charges on one side of the membrane than the other, then there is an electrical difference along that membrane. In most excitable cells, the electrical gradient is largely based on the concentration of sodium ions and potassium ions. Typically, when a cell is not actively excited, there will be more positively charged ions outside of the membrane, which makes the charge at rest inside the membrane negative. These electrochemical gradients are maintained by sodium-potassium pumps, which use ATP to remove positive charges from the cell.

When it's time to become active, voltage-gated ion channels, or sodium channels, will open once the membrane charge reaches the threshold voltage, or the minimum charge necessary for a cell to become active. When the threshold voltage is reached, which is typically at -55 mV, the ion channels open in order to allow positive charges to rush inside the cell. This is known as depolarization, which is the process of becoming positively charged.

After a cell depolarizes, it will eventually reach a maximum positive charge. At this point, the cell will try to return to rest by removing positive charges. This is usually done by potassium ions leaving the inside of the cell to cause the cell to become more negative. Eventually, after the charge gets closer to the original resting membrane level, the sodium potassium pump will re-establish its original -70 mV charge.

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