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The Orexin System



If you have narcolepsy, you really need to learn something about orexin.


The reason you've never heard of orexin is because it was only discovered in 1998.   (Two different research teams found it at the same time.   One named it orexin, the other named it hypocretin.  Both names are used in the scientific literature.   I prefer orexin and will use it exclusively in my documents.)   The new protein was quickly linked to sleeping and eating. Orexin injection or blocking altered feeding habits in rats. Dogs with orexin mutations exhibited cataplexy and other symptoms of narcolepsy. And human narcoleptics were shown to have undetectable levels of orexin in their systems.   Further studies have shown that narcoleptics are missing most of their orexin cells, and that they also degenerate over the course of Parkinson's disease


Orexin is a neurotransmitter, a chemical "signal" released by neurons. Orexin producing cell bodies are found in the brain, and only in the brain. Orexin neurons are located in the hypothalamus region of the brain.  In recent years research has shown that although orexin cell bodies are confined to a small area, they send axon fibers all over the body, releasing orexin and initiating and regulating many processes.


There are two types of orexin, A and B. Type A is responsible for most of the known activity and I will simply default to the term "orexin" for the A version if not otherwise specified.


In the brain it acts like a neurotransmitter, activating other neurons.

In the body it acts like a hormone, stimulating organ activity.


At its most basic level orexin stimulates you to find food.

When you're hungry orexin levels are high. You are awake and alert and mobile.

After you eat, your orexin levels go down and you become less active.

And when you sleep, they are very low.


Conciousness- is pretty vital to food acquisition. Cells in the eyes are connected to the orexin cells. When light hits the retina they send impulses to the orexin cells and they begin firing. This is what wakes you up in the morning.  (And puts you to sleep at night, you shouldn't be out at night foraging for food, it's too dangerous.)


Mood- orexin stimulates the dopamine and serotonin reward systems. So the idea of food makes you happy and you feel motivated to go get some.


Energy level-

Orexin stimulates the Locus Coeruleus (LC). More orexin fibers go to the LC than any other place in the body.

(Remember that. It comes up a lot. But no, I don't know how to pronounce it...) (here it is)

The locus coeruleus is a brain region that regulates overall activity level and sensitivity by releasing adrenaline.  

More orexin, more adrenaline, more energy.

Less orexin, less adrenaline, less energy.


Orexin also regulates the vagus nerve via the LC.

The vagus nerve controls the autonomic reactions of breathing and heartrate under stress. 

That comes in handy when you're hunting.



Memory-   orexin stimulates the hippocampus which is involved in geospatial and emotional memory.  This helps you remember where food is, and also nearby dangers. 


Cognitive function-  orexin stimulates the prefrontal cortex which is responsible for attention and calculation.  This is fundamental to complete a successful hunt or forage or farming season.  This area enables you to plan where to go and how to get there.  What to take.  What the relevant weather or current events are.  What to do in case of adverse events. 


Pain-  orexin innervates the cranial and spinal nerves and acts as a pain reliever.  This may facilitate endurance during a hunt, or more likely, periods of starvation.



Orexin fibers extend to the stomach, intestines, and pancreas.   Changing orexin levels stimulate them to digest food.  Orexin regulates stomach mucous and gastric acid secretion, insulin release, and intestinal movement.  Orexin receptors are found in fat tissue.  Orexin also modulates alcohol craving and tolerance.


technical note



This one isn't really food related, but it's of interest to most people:


Reproductive-  Orexin activity is also found in the ovaries, testes, and placenta.    Orexin affects production of both sperm and ova.

There is some reciprocal reinforcement also-  sex is strongly linked to the reward systems associated with orexin, and orexin production is stimulated by oxytocin which is produced during sexual contact.

Orexin also reacts with sex hormones to produce different effects in men and women.




Orexin cells aren't ordinary, they have special properties, and orexin fibers innervate many areas of the body. I really hate the computer metaphor, but the orexin system actually is like the operating system of the brain. It regulates metabolic resources- switches other parts of the nervous system on and off. When it's not working properly, a whole lot of other things can go wrong.






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