How Does Caffeine Work in the Brain?

 

First, How Does Sleep Work Without Caffeine?

  To fully understand how caffeine works a person must understand how sleep works.  The chemical adenosine accumulates in the brain when it is awake and active.  In the basal forebrain, the cells are responsible for wakeful arousal and have adenosine receptors that inhibit them.  It is as if they are moving really fast and then the adenosine attaches to them and slows them down, causing sleepiness.  They actually inhibit them by releasing a second messenger in the cell, which increases the activity of certain genes, leading to a long-lasting affect that sustains sleep for hours.  That is how sleep works.

 

So, How Does Caffeine Affect Adenosine and Sleepiness?

  Caffeine belongs to the xanthine chemical group. Adenosine is a xanthine that is naturally occurring in the brain, used as a neurotransmitter at some synapses. Because of their relation, caffeine looks a lot like adenosine to nerve cells and therefore binds to adenosine receptors in the basal forebrain.  The cells then can no longer sense adenosine because caffeine is taking up the receptors.  Instead of slowing down, the nerve cells speed up and stop the person from getting tired. 

 

What Else Does Caffeine Affect in the Brain?

  As a result of the blocked adenosine, there is increased neuron firing in the brain, which causes the pituitary gland to think that there is some sort of emergency.  It then releases hormones telling the adrenal glands to produce adrenaline.  This has many effects on the body– liver releases sugar into the blood for extra energy, pupils dilate, heart beat increases, breathing tube open more, etc.  Caffeine is also said to increase dopamine levels much like amphetamines do, which produces a euphoric effect.  It potentially does this by slowing the rate of dopamine re-uptake.  

 

What Are the Effects of Caffeine on the Brain?

        In answering this question, I am referring mainly to coffee drinkers, which I myself am.  That is how most people consume caffeine.  Adenosine reception is important to sleep, especially deep sleep.   There is a cycle that can exist when people drink coffee after a certain point in the day.  Caffeine has a half-life of 6 hours, which mean that if a person drank 200mg of caffeine, 1-2 cups of coffee, at4:00pm, then at 10:00pm, 100mg of caffeine would still be in the system blocking adenosine reception.  The person may fall asleep, but would miss out on the benefits of deep sleep.  That increases tiredness the following day, also increasing the desire for coffee.  When in this cycle, some people experience splitting headaches, and many repot extreme tiredness and depressed mood.  The headaches have been found to be most likely from the dilation of blood vessels in the brain.  The depressed mood is most likely just a rebound from the recent manipulation of dopamine. 

 

What is this analogous to?

        My analogy is of a computer lab that many students need to use to get important work done.  Think of each computer as an adenosine receptor and each student as adenosine.  When they are all seated, the lab is quiet without much movement.  This would be when a person becomes tired. One day a bunch of other students beat them to the computers and started playing games on them.  The computer lab then becomes loud and busy with activity.  These game-playing students are like caffeine getting in the way of the adenosine.  The pituitary gland could be like the faculty, whom is alerted of the situation in the lab and panics because the hard-working students can’t get their work done and there are a bunch of them standing in the hallway outside the lab.  The faculty then send other people, who are analogous to adrenaline, to the lab.  These people cause even more activity.

 

By Mandy Lind

 

Resources:

Biological Psychology 8^th Ed. By James W. Kalat

http://faculty.washington.edu/chudler/caff.html

http://science.howstuffworks.com/

        question531.htm