Relative Refractory Period: Definition & Significance

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

This lesson is about the relative refractory period - the amount of time that a neuron needs additional stimulus to be able to send an action potential. In this lesson, you will learn how neurons communicate, what the relative refractory period is, and why it is important for our bodies.

Neural Communication

Ever notice how if you touch something warm, in a short period, it's no longer such a shocking sensation. You become desensitized to the feeling. Wonder why you become desensitized to certain sensations over time? The answer is the relative refractory period during communication between brain cells, or neurons in your brain. Neurons communicate through both electrical and chemical signals. Electrical signals run through one neuron from the dendrites, the part that receives signals, through the axon, the part that sends signals. Below is a picture of the electrical signal moving through an axon.

Electrical signal moving through an axon
Electrical signal moving through an axon

At the end of the axon, the synaptic terminal, the electrical message is converted to a chemical message, called a neurotransmitter. Right after an action potential moves down the axon, there is a period that it is harder for a neuron to send another signal. This period is called the relative refractory period.

How Does the Action Potential Work?

When a neuron gets a strong enough signal to fire an action potential, called the threshold, several things happen. First, voltage-gated sodium channels open, triggered by a positive charge inside the cell. Once they open, sodium, a positively charged ion, rushes in. The cell becomes more positive or depolarized. This action is similar to a concert venue where, when the doors to the concert open, all the fans rush inside the venue. The venue is like the neuron, and the concert goers are like the sodium. After a short period, the sodium gates slam shut, and no more sodium enters the cell. This action is similar to the doors closing at a concert and not allowing late fans to enter.

Next, voltage-gated potassium channels open and potassium, another positively charged ion, rushes out of the cell because there is more potassium inside the cell than outside. This action is analogous to the end of a show when fans rush out of the cell. But remember, this is a different ion, potassium, not sodium, which leaves the cell. Below is an image of the voltage-gated potassium channels allowing potassium to leave the cell.

Voltage gated potassium channels shut, and open
voltage gated potassium channel

This action causes the cell to get more negative and return to its resting potential or normal voltage. However, the cell becomes more negative than its resting potential, making it harder to get to the threshold voltage to send an action potential.

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