Right, I’m terribly sorry about the delay in posting this week. The snow plus a lack of home internet lead to it being impossible to get this post from my laptop to the blog in time for yesterday morning. It’s a shame because this post would have been lovely and appropriate for a cold Monday morning, but hey, it’ll serve a cold Tuesday just as well. Normal posting shall resume from here on in, as a nice Virgin technician is coming to install wireless in my new house today (I’m hoping this’ll make it feel less like a holiday home that has all my books in it).
I think caffeine could reasonably be described as the drug that keeps the nation going; perhaps this is something of an overstatement although I do know such a large number of people who simply can’t function properly until they’ve had their morning tea or coffee. They wake up, bleary-eyed and fuzzy headed and stumble to the kitchen to pop the kettle on and brew an energising beverage. They sip their tea or coffee until their brain starts to feel awake again, firing on all cylinders, ready to take on the world. That’s what caffeine does; it wakes your brain up.
Your brain chemistry is incredibly, seriously batshit complicated. In amongst the tangle of neurotransmitters and nerve cells and overlapping systems there is a molecule, adenosine, and a group of receptors, the adenosine receptors. Adenosine has a lot of different roles in the body, it’s quite a busy and important molecule; but in the brain one of the things that it does is to slow down nerve cell activity. Over periods of prolonged neural activity, when you’re hard at work, thinking, processing, generally doing stuff, adenosine levels in the brain start to increase. Adenosine is like a kindly parent, one who notices that you’ve been working too hard, and that you might need a break. As adenosine builds up, more and more of it binds to adenosine receptors in the brain, sending out messages that suppress neural activity, forcing your mind to slow down and become drowsy. Your mummy molecule is playing soothing music and telling you it’s bedtime.
This is very lovely and caring of adenosine, it wants your brain to relax, it’s urging you not to overdo it, to sit down and have a break. It probably wants you to eat a piece of cake too (there’s no scientific basis for this statement in the slightest but I always hope that my molecules want me to eat cake). The problem for you is that sometimes your brain is slowing down, and you’d actually rather like it to be speeding up, because you have stuff to be doing. This is where caffeine comes in.
Caffeine is a stealthy molecule, a molecular ninja. It looks almost exactly like adenosine, and the adenosine receptor cannot tell the difference. Caffeine can therefore sneakily bind to the adenosine receptor, in place of adenosine. Once bound, however, caffeine has an entirely different effect on the receptor, instead of sending soothing messages to slow down, rest and sleep; it blasts out heavy metal and wakes everything the hell up. Your neurons don’t get the message to slow down, so they keep on firing, working away. Your brain is kept awake by loud thumping music and lots of quickly firing neurons, getting on, doing things, being awake and alert and ready for action. That’s how caffeine makes you feel wide awake, it stealthily hijacks your adenosine receptors and stops adenosine from sending your brain to sleep.
Caffeine doesn’t just wake up your brain, though. It can also increase your heart rate; it does this in two ways. First, your pituitary gland, the observant little fellow that it is, notices all the increased neural activity going on because caffeine usurped adenosine. It interprets this increase in activity as an emergency situation, probably because it doesn’t like loud music, and reacts by releasing stress hormones, which act to increase your heart rate, amongst other things.
However, caffeine can also have a direct effect on heart cells. As well as being a super stealthy adenosine mimic, it is also an inhibitor of an enzyme, phosphodiesterase. This enzyme is usually involved in regulating the production of cAMP, which in turn is involved in the complicated regulation of how regularly your heart beats. When caffeine is around, this regulatory system doesn’t run as normal, it’s probably the equivalent of the effect a sprinkle of snow has on the regular running of the British rail system. Although in this case your heart doesn’t stop running, it actually runs faster, so perhaps not after all. It would probably be better never to drink a molecule that does to your heart what snow does to the trains in London.
Either way, that’s how caffeine wakes up your brain and speeds up your heart rate, and that’s why some people find drinking it at night stops them sleeping, because it inhibits some of the drowsy signals your brain uses to switch off, using stealth and loud heavy metal music.