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What Are Orexins?

Medically Reviewed by Brunilda Nazario, MD on July 08, 2021

Orexins are chemicals in your brain that help your body stay awake. Orexins also make sure that rapid-eye movement (REM) sleep -- sleep with intense dreams that happens about an hour after you fall asleep -- doesn’t happen at the wrong times.

You might also hear orexins called hypocretins, but they’re the same thing.

How Do Orexins Work?

Orexins are neurotransmitters, which are chemicals in your brain that send messages from one neuron (a nerve cell) to another.

Only a small group of neurons in the hypothalamus (a part of your brain that controls behaviors like sleep, hunger, body temperature, and arousal) make orexins. Your brain has billions of these neurons, but a select cluster of them -- about 100,000-200,000 -- make orexins.

When you’re awake, those neurons send out orexins. The orexins then bind to certain orexin receptors on other neurons. When that happens, the amount of activity of those neurons goes up. In other words, these orexins encourage neuron activity so that REM sleep is blocked and you’re awake and alert. This isn’t the case when you have narcolepsy with cataplexy.

How Are Orexins Related to Narcolepsy?

Narcolepsy is a chronic condition that happens when you don’t have enough neurons that make orexins. People with narcolepsy are usually very sleepy during the day.

If you have narcolepsy, you might also have sleep paralysis, where you’re awake but can’t move. It usually happens just as you’re falling asleep or when you’re starting to wake up.

Some people with narcolepsy also have dream-like (you might hear them called hypnagogic) hallucinations. You might see, hear, or feel things that aren’t really there. These can be scary and usually happen when you feel sleepy or when you’re falling asleep.

Some people with narcolepsy experience cataplexy, where your muscles are paralyzed or weakened for a short period of time. Although you might not be able to move, people who experience cataplexy are conscious and can hear what’s happening around them. Cataplexy is usually triggered by strong emotions, like when you’re laughing, joking around, or angry.

Although not everyone with narcolepsy has it, scientists have discovered that not having enough orexins can cause narcolepsy with cataplexy. Here’s what happens:

If you have narcolepsy with cataplexy, the neurons that make orexins die off. As a result, you’ll feel sleepy for long periods of time and your body won’t have much control of REM sleep. That’s exactly why some people with narcolepsy have cataplexy and experience hallucinations that seem real.

Although scientists don’t know as much about people who have narcolepsy without cataplexy, many say that it’s most likely tied to orexins. Some researchers think that in this case, the orexins don’t die off but become damaged somehow, meaning there are fewer, less serious symptoms in people who have narcolepsy but don’t experience cataplexy.

People with narcolepsy often feel sleepy or not awake. Lots of scientists believe that this is because of sleep state instability, where the line between being asleep and being awake becomes less clear. The result is that people with narcolepsy might not be completely awake during the day and don’t get good, healthy sleep at night.

WebMD Medical Reference

Sources

SOURCES:

Healthy Sleep, Harvard Medical School and WGBH Educational Foundation: “The Science of Narcolepsy.”

Frontiers in Neurology: “Narcolepsy and Orexins: An Example of Progress in Sleep Research.”

Brain Facts, Society for Neuroscience: “The Neuron.”

Cleveland Clinic: “Sleep Basics.”

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