Depolarization (Definition + Process) - Practical Psychology (2023)

Depolarization is one of the phases of nerve conduction and action potential. Some ions play an important role in nerve transmission. The plasma membrane of our cells often has a charge difference between the inside and the outside due to differences in electrolyte content. These differences are called polarization.

The loss of polarization is called depolarization and is usually associated with nerve impulses. Depolarization is a rapid change within a cell in which the cell undergoes significant electrical changes. Most batteries typically have a negatively charged internal environment.

Depolarization is an important medical concept that occurs in cells. Here's everything you need to know about depolarization.

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Everything You Need to Know About Depolarization

How do stimuli cause depolarization?

Can the heart be depolarized?

Depolarization vs. Repolarization vs. Hyperpolarization


Everything You Need to Know About Depolarization

Suppose there is a nerve that never communicates with other people. If so, how does information get from one nerve to another? magic? not completely. In order for communication between nerves to occur, a certain action potential must be reached.

A semipermeable membrane covering the cell separates the cell's internal environment from the external environment, in most cases plasma. The ratio of positive and negative ions in cells is related to the outside world.

This creates an electrochemical gradient. It can be measured by comparing the total charge inside and outside the battery. Membrane potential is related to this distinction. Cells can regulate ion concentrations using protein-based membrane channels.

When the channels are open, certain ions can cross the membrane. Unique pumps in certain channels use energy to push ions through. Let's imagine that during polarization, the inside of the membrane is negatively charged and the outside is positively charged. Charge changes inside and outside the cell are caused by the migration of electrolytes across the plasma membrane.

Biological cells, especially electrically excitable cells such as cardiac cells and neuronal cells, maintain membrane potential by separating ions across the plasma membrane. In other words, the membrane is electrically polarized, usually negative on the inside and positive on the outside. Depolarization is a decrease in the polarity of the membrane potential.

Depolarization is a shift in the electrical charge of a cell that causes the inside of the cell to always be more positive than the outside. Electrical or excitatory stimulation that increases the cell's voltage causes voltage-gated ion channels in the cell to open. Positive sodium ions flood the cell through these ion channels, changing its internal charge from negative to positive.

An electrostatic resting potential exists in the membrane of a resting nerve cell. Sodium ions and potassium ions are actively pumped by the sodium-potassium pump to the diffusion gradient on both sides of the membrane, maintaining this balance. Both ions migrate rapidly when membrane permeability is altered and depolarizes the resting membrane potential in a wave-like manner.

How do stimuli cause depolarization?

In response to specific signals, cells open their membrane channels, allowing ions to pass through the membrane, balancing the positive and negative charges on both sides. This means that due to this equilibrium, the cell loses its selection pole.

So it's caused by some sort of stimulus. For example, if a bug is crawling on your skin, it evokes a sense of touch. This generates an action potential in a nerve located deep under the surface of the skin.

The sense of touch triggers nerves and can generate impulses in the nerves. This trigger causes nerves to transmit false information that crawls under your skin. To trigger a nerve, the shock must be strong enough to generate an action potential of 150 mV.

In resting cells, the membrane charge is negative compared to the outside world. Take spinal cord neurons, for example. The resting membrane potential of these motor neuron membranes is -70 mV, which means that the inside is -70 mV lower than the outside.

When this potential decreases or the inside becomes less negative compared to the outside, eg -50 mV, the membrane is considered depolarized. The resting voltage of living cells is typically between 70 and 90 millivolts, which allows them to be polarized like tiny biological batteries.

These resting voltages are reported as negative values, such as -70 mV, because the interior of the cell membrane is usually negative compared to the outer surface. Simply put, neurons respond to stimuli such as touch, sound, light, and other types of stimuli. Neurons execute impulses and communicate with various types of cells, including muscle cells, and with each other.

Action potentials help neurons transmit information. The extracellular environment contains sodium and potassium ions. The charge is -70 mV, known as the resting membrane potential because there is no stimulus and all gates are closed. When a neuron is activated, the electrical current causes voltage-gated sodium channels to open.

Because of their positive charge, sodium ions penetrate the neuron's cell membrane and begin to increase the charge inside the cell. A localized depolarization, also known as a localized potential, means that it occurs at a specific point in the cell. Although the event can spread from the origin to a limited area, this voltage change does not spread very far.

Compare this to dropping a small pebble into a pond, which, due to the resistance of the water, creates ripples that travel a short distance before disappearing. Action potentials, on the other hand, are self-propagating. If one triggers the one in front of it, it triggers another, and so on, like a cascade of falling dominoes. This causes the signal to move away from the stimulation site.

Can the heart be depolarized?

Depolarization is the process by which the voltage inside a cell drops to zero. It is well known that every heart cell is polarized. This is demonstrated by placing tiny electrodes in individual cells and connecting them to a measurement device such as an oscilloscope. It was then found that the inside of the cell was approximately 90 mV negative compared to the outside.

The -90 mV quickly goes to zero when the cells receive a signal from nearby muscle cells that make up the heart's signaling system. After about 200 milliseconds, the cells begin to repolarize. After about 300 milliseconds, their insides are again at -90 mV compared to the outsides.

Calcium released from depolarization in the cell causes the cell to shrink. Contraction of heart cells causes the volume of the ventricles and atria to decrease, helping to pump out blood that accumulates in them during diastole, when the ventricles do not contract.

The sinoatrial node in the right atrium contains modified, specialized musculature that depolarizes itself. Depolarization of this tissue then extends to the atrial myocardium and the atrioventricular node at the junction of the right atrium and ventricle.

The unique conductive tissue of the ventricle rapidly conducts depolarizing signals to its inner surface. The ventricles then contract as the ventricular muscle depolarizes from the inside out. Depolarization signals can be observed by inserting electrodes through a vein into the heart.

Subsequent depolarization and repolarization of the cardiomyocytes produces the detected signal. An electrocardiograph, also known as an electrocardiogram, is a sensitive voltage indicator that detects movement in areas of depolarization. By placing electrodes on different parts of the chest, it is possible to follow the pattern of depolarization that propagates through the chest.

The tension created by depolarizing each muscle cell in a specific order is called cardiac depolarization. Wondering if depolarization only happens in heart and neuronal cells? Depolarization occurs in many other areas of the body, such as the ears.

The flow of ions across the membrane into hair cells increases with increasing voltage. The influx of ions depolarizes the cells, creating an electrical potential that ultimately sends signals to the brain and auditory nerves.

Why is depolarization important?

Depolarization is critical because it enables communication across the cell membrane and initiates the opening and closing of membrane potential-sensitive channels. These channels are called voltage-controlled channels.

Depolarization allows neurons to rapidly transmit information from one end of the cell to the other. The fastest way to send information through a very long membrane is depolarization, which is why it is used. Some neurons are known to be several feet long, so depolarization is convenient.

Reproduced for illustration purposes. After fertilization, the egg needs to react quickly to keep other sperm from getting in. In response to the first sperm, it will do this by depolarizing its membrane. As a result, the whole egg responds quickly, blocking the entry of subsequent sperm.

Depolarization vs. Repolarization vs. Hyperpolarization

Although all three terms have the same suffix, their meanings are completely opposite. To understand the difference between these terms, it is important to keep two facts in mind. This means that the outside of the cells has more sodium than the inside, which in turn has more potassium.

Another fact is that the outside of the cell membrane is more positively charged. On the other hand, the inside of the cell membrane is more negatively charged. With this in mind, while there is positive potassium in the cell, something else in the cell membrane causes it to be more negatively charged.

When talking about depolarization and repolarization, you are dealing with membrane potential. This is the difference in charge between the inside and outside of the battery. In a resting state, the cell membrane is said to be polarized. This is because there are differences in fees. Therefore, at this time, all channels are closed.

Depolarization occurs when sodium channels open. As mentioned above, since there is more sodium on the outside of the cell, once these channels open, positive sodium begins to enter the cell. This causes the inside of the cell to become more aggressive. So it is depolarized because there is less difference between the inside and outside of the cell.

Repolarization, on the other hand, occurs when sodium channels close and potassium channels open. Since the potassium channels are now open, all positive potassium begins to flow out of the cell. This causes the charge to reverse, making the outside more positive and the inside more negative.

In addition, potassium channels remain open much longer than is required to ensure regular rest in the membrane. This is where hyperpolarization comes into play. This happens when the inside of the cell becomes more negative than it started out as positive potassium continues to leak out.

Differences between inside and outside the cell membrane were restored. Anything below normal resting membrane potential is hyperpolarization. These sodium and potassium pumps return to their normal resting state.

In summary, after depolarization, sodium channels open and sodium rushes into the cell, making the inside of the membrane more positive than the outside. During repolarization, sodium channels close, potassium channels open, and potassium flows out of the cell, making the interior negative again.

Hyperpolarization is when the interior of the cell membrane becomes more negative than at rest because potassium leaves the cell during repolarization.


During depolarization, the charge distribution in the battery changes, resulting in a much less negative charge in the battery. The charge imbalance inside and outside the muscle or nerve cell membrane disappears due to changes in sodium ion permeability and influx.


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