Action Potential

We have all ever wondered how our body actually works. How is it possible that the brain and nervous system regulate everything? The answer is: the action potential, the messenger that transfers information from the nervous system to all other cells.

Let’s see more about the action potential below and how it helps us better understand how the body works.

What is the nervous system?

The nervous system is a complex network of structures made up of the central nervous system (brain and spinal cord) and the peripheral nervous system, made up of ganglia and nerves.

This is responsible for maintaining control of the body and regulating the function of all organs and systems. 

  The nervous system is made up of two types of cells:

• Neurons: A neuron is a type of nerve cell that receives and sends messages (via a weak electrical current) from the body to the brain and vice versa.
  • Neurons are responsible for originating, conducting and transmitting nerve impulses between them through a process called synapses.
  • Only in the human brain we find approximately one hundred billion neurons.
• Glial cells: there are different types with different functions. These include protection against infectious agents or the structural support of neurons.

The nervous system basically works by taking environmental stimuli and transforming them into electrical stimuli through a process called ‘transduction’. In this process, nerve receptors transform the received stimulus into a nerve impulse.

Any type of external information that we receive is translated into a specific code, which is used by neurons to communicate with each other and with other cells. This code is based on two types of signals:

• Electrical: they  arise in the dendrites and in the soma. They are in charge of receiving the information.
• Chemical: they  are mediators of the information that is transmitted from neurons to the cells of the body.

What is the action potential?

That said, we can define the action potential or electrical impulse as  an electrical discharge wave that is transported along the cell membrane.

It occurs when there is an exchange of ions across the membrane of the neuron. Ions are the body’s way of transferring information from one tissue to another. 

But how does it happen? It is produced in the soma, also called the nucleus of the cell. It travels down the axon (a long, thin extension of neurons) until it reaches the end, known as the terminal button.

Once the action potential reaches the terminal button of the neuron, it is responsible for secreting substances chemical : neurotransmitters. These are messengers that allow connectivity from one neuron to another.

Phases of the action potential

The neuron is a cell and is protected by the cell membrane. The electric charge inside and outside the membrane are different.

When the cell is at rest it has a voltage (between 30 to 90 mV), that is, it is not altered. In the membrane there are proteins that act as ionic channels for the transport of potassium and sodium.

Sodium is outside the membrane and tends to enter. While the potassium is in and looking to get out.

1. Depolarization

In the first phase,  the potential difference on the inside and outside of the cell is less. This means that the probability that the neuron responds and transmits the information increases.  When this event occurs, what is known as an action potential or nerve impulse occurs.

However, for this process to be faster it is necessary to have an initial depolarization of a certain magnitude, of -55 mV.

In this way the potential changes, since the interior of the neuron becomes positive and the exterior negative. That is, sodium invades the interior of the cell by opening its channels.

This means that the electrical charges are sufficient for the membrane potential to reach the excitation threshold. Therefore, there will be an action potential when depolarization is sufficient, otherwise it will not occur.

2. Repolarization

In this phase,  the potential difference becomes negative again. While sodium channels open during depolarization and invade the cell, voltage-gated potassium channels also open much more slowly.

Then, the potassium is responsible for returning to the negative charge. This leaves the membrane so that the cell recovers its natural state of rest in which no channel is opened.

3. Hyperpolarization

As already mentioned, sodium channels are very slow and an increase in the value of the membrane potential in the cell is required. , it is say, hyperpolarize. Thus, the  membrane potential can become more negative.

Therefore,  there is a greater difference in the distribution of electrical charges between the inside and outside of the cell. 

Eventually, the neuron becomes inactive, becoming a resting cell. In this way, it reaches the last phase where each ion returns to its original place. Therefore, the potassium goes back inside the membrane and the sodium outside.