It's a well-known fact that coffee keeps you awake. It's similarly well-known that this is down to the fact that coffee contains caffeine. But do you know why it is that caffeine has this effect? Is it the caffeine itself? Or is something else going on in your body to stop you feeling drowsy?
Caffeine has the effect of blocking the chemical that causes sleepiness from interacting with the brain. Whilst this may sound a bit scary, it's a naturally-occurring phenomenon where a chemical called adenosine is prevented from carrying out its normal function.
Adenosine is produced naturally in the body as a result of our daily routine. Our brains feature adenosine receptors, that this chemical binds itself to, which helps to slow down our brain's nerve cell activity, leading us to get drowsy and fall asleep.
As a by-product of this binding, blood vessels within the brain are dilated, which serves to let more oxygen to the brain whilst you are asleep. It seems funny that one of the chemicals that is produced by exercise - adenosine - has the counter-intuitive effect of causing you to fall asleep, but natural that it would allow more oxygen in.
From the point of view of our nerve cells, caffeine is very similar to adenosine. This allows the caffeine to bind itself to our adenosine receptors, blocking the adenosine from doing so. Rather than slowing down nerve cell activity, though, this blocking of the adenosine serves to increase it.
Caffeine also has the opposite effect from dilating the blood vessels, leading to them constricting. If you have particular types of headache, this is the reason some cures include caffeine, to restrict the flow of pain-causing blood cells getting to the brain.
With the caffeine blocking the adenosine, increased neuron activity occurs within the brain. This leads to our body's thinking there is some type of emergency situation occurring, which leads to the release of hormones that trigger adrenalin, thus preparing us for "fight or flight" in extreme cases.
Everyone realises that the last thing you need when you want to get to sleep is a boost of adrenaline. Which is essentially why coffee keeps you awake - with the adrenaline leading to tense muscles, a faster heartbeat, and even a feeling of excitement that is certainly not conducive to dropping asleep.
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