This blog post is designed to give you basic information about caffeine. Why? Well, caffeine is an interesting compound. It is a legal drug, socially acceptable and cheap to buy. It is also frquently in the media, being linked to diseases such as Cancer and MS, but it is also associated with cognitive enhancement of memory and concentration. It's always worthwhile to question whether there is any validity to such claims: could caffeine possibly have any influence on concentration or memory for example? I will attempt to address some of these questions in future posts, but for now this is simply an introduction to what caffeine is, what it does and how it does it.
Caffeine is a small chemical compound with stimulant properties. Stimulants include a range of interesting compounds such as the amphetamine compounds MDA, MDMA, and methamphetamine. All stimulants promote increased levels of alertness, increased reaction time, and some degree of euphoria. Unlike amphetamine based stimulants however caffeine does not have psychedelic effects. Caffeine occurs naturally in the seeds of coffee plants, tea plants and in the cocoa beans, used to make chocolate. It is also added to synthetic products such as energy drinks, or painkillers where it is used to amplify their pain-relieving effects.
CAFFEINE IN THE BODY
Once ingested caffeine rapidly enters the blood stream. From here it makes it's way to the brain, and stimulates the cells of the central nervous system, (CNS). Approximately 12 hours after ingestion the caffeine molecules have been eliminated with the help of liver enzymes. In fact, the elimination of caffeine from the body is very complicated and involves a single molecule of caffeine undergoing 24 distinct modifications to its structure before it can finally excreted in the urine.
Chances are you have never heard of adenosine, but to make sense of how caffeine interacts with the body I need to introduce and discuss the role of this new molecule. Adenosine is a small chemical compound called a purine nucleoside. It occurs naturally in our bodies and is involved in a number of important functions.
The exact function of adenosine depends on where it is the body. For example, adenosine in the heart is required for maintaining a regular heartbeat, but it's also required for blood vessel dilation, smooth muscle contraction, neurotransmitter release, and metabolism of fat. In fact, the effects of adenosine on the heart are exploited in medicine where it is used to treat instances of supraventricular tachycardia. Interestingly, adenosine is also responsible for regulating sleep. I will go into more detail on this below.
ADENOSINE AND ATP
Our brain utilises an enormous amount of energy in the form of a chemical called adenosine triphosphate, or ATP. In the same way that ashes are the waste product of burning coal, adenosine is the waste product of burning ATP. Subsequently, as we continue to utilise our brains throughout the day, the levels of adenosine continue to rise. Rising levels of adenosine in the brain result in a person feeling tired, and ultimately going to sleep. While sleep still uses a lot of neural activity in the form of dreams, the rest of the body is on standby, giving it a chance to replenish its stocks of ATP.
CAFFEINE AND THE ADENOSINE RECEPTOR
ADENOSINE AND ATP
Our brain utilises an enormous amount of energy in the form of a chemical called adenosine triphosphate, or ATP. In the same way that ashes are the waste product of burning coal, adenosine is the waste product of burning ATP. Subsequently, as we continue to utilise our brains throughout the day, the levels of adenosine continue to rise. Rising levels of adenosine in the brain result in a person feeling tired, and ultimately going to sleep. While sleep still uses a lot of neural activity in the form of dreams, the rest of the body is on standby, giving it a chance to replenish its stocks of ATP.
Any molecule that interacts with a receptor in the brain is said to have a psychoactive effect, and this includes naturally occurring compounds such as dopamine and serotonin, associated with mood, movement and appetite, or acetylcholine associated with memory formation. Both adenosine and caffeine molecules mediate their psychoactive effects by binding with a specific protein molecule called the adenosine receptor, or ADR for short. Receptors are protein molecules found on the outside of cells where they act mediators between the inside of the cell and the outside environment. Receptor proteins are the primary way in which cells obtain information from their surroundings.
THE ADENOSINE RECEPTOR (ADR)
The ADR receptor is found in different regions of the body, primarily the brain, but also in the heart. The structure of this receptor molecule with caffeine bound to it is shown below. The images below show the ADR, from the front and top. The last image shows a zoomed in shot, with some of the protein cut away to show caffeine molecule more clearly. You'll notice the receptor protein is quite large, and somewhat tubular in shape. This tubular shape allows it to position itself in the cell membrane, an ideal location for relaying messages between the inside and outside of the cell. Notice, the caffeine molecule, shown in yellow, binds at the top of the receptor protein. All of the effects of caffeine, alertness, changes in heart-rate etc, are the result of caffeine binding this receptor protein. The binding of caffeine to this receptor instigates a whole new cascade of events that propagate the effects of caffeine all the way through the body and brain. The details of this cascade are too tricky to explain here, but for the moment all you need to know is that the result of adenosine binding to the ADR is that neural cell activity is slowed in preparation for sleep. Caffeine interferes with this system by binding to the same location as adenosine does, essentially blocking access to the ADR, and preventing adenosine from doing its job.
NEUROANATOMY 101THE ADENOSINE RECEPTOR (ADR)
The ADR receptor is found in different regions of the body, primarily the brain, but also in the heart. The structure of this receptor molecule with caffeine bound to it is shown below. The images below show the ADR, from the front and top. The last image shows a zoomed in shot, with some of the protein cut away to show caffeine molecule more clearly. You'll notice the receptor protein is quite large, and somewhat tubular in shape. This tubular shape allows it to position itself in the cell membrane, an ideal location for relaying messages between the inside and outside of the cell. Notice, the caffeine molecule, shown in yellow, binds at the top of the receptor protein. All of the effects of caffeine, alertness, changes in heart-rate etc, are the result of caffeine binding this receptor protein. The binding of caffeine to this receptor instigates a whole new cascade of events that propagate the effects of caffeine all the way through the body and brain. The details of this cascade are too tricky to explain here, but for the moment all you need to know is that the result of adenosine binding to the ADR is that neural cell activity is slowed in preparation for sleep. Caffeine interferes with this system by binding to the same location as adenosine does, essentially blocking access to the ADR, and preventing adenosine from doing its job.
Lets imagine the brain is a vast computer network of CPUs and ethernet cables. In the brain, the ethernet cables are called neurons, and the CPUs are the nucleus of those neurons. There are some similarities between these two systems, they both have a bandwidth associated with them, i.e, a maximum rate of information transfer. They both have insulation to prevent loss of the signal, as well as eliminate cross-talk between wires, and in both systems information is rapidly transferred in discrete packets. For Ethernet cables this is a purely electrical signal, but for neurons this is mix of both electrical and chemical signalling.
CHEMICAL SIGNALLING
The long tendril like structures of neurons are called dendrites. Dendrites are responsible for information transfer in the form of small charged molecules moving rapidly through the cells. The interface between two dendrites is called a synapse. The synapse is the region where electrical signals become chemical signals. If you want to interfere with information transfer in the brain the synapse is one of the places you can do it. This is where many of the commonly used drugs mediate their effects.
STIMULANTS AND INHIBITORS
To regulate all the traffic that occurs between neurons, the brain releases a mix of stimulant and inhibitor molecules. Both types of molecule occur naturally, being made by the brain cells themselves. Stimulants promote signalling between neurons, while inhibitors slow it down. Together stimulants and inhibitors provide a feedback mechanism, so when energy stores in the body are low we attenuate our neural activity accordingly. If you drink a cup of coffee, the caffeine molecule takes the place of adenosine at the ADR, and the signal that normally comes from adenosine that says "slow neural activity" is now missing. This results in a brain without "brakes" as it where and we continue to fire off signals from our neurons despite the need for rest. By ingesting caffeine we have essentially hijacked our own brains and decided to over-ride our own internal feedback mechanisms for determining when we should rest. This is pretty cool in my opinion.
WAIT..I'M CONFUSED
Listen, I don't blame you. In order to discuss this seemingly simple molecule, caffeine, I had to introduce a lot of concepts and terminology. Biology is complicated like that, there are lots of interactions occurring all the time. It is a complicated topic, but here is a summary that should help.
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| Image on the left shows an artists representation of neurons, brain cells. The long tendril like structures are called dendrites. The synapses are the gaps between connections, where the electrical signal becomes a chemical signal. This is analogous to ethernet cables, right, which also carry electrical information, are insulated, and connect to each other via switches/synapses. |
The long tendril like structures of neurons are called dendrites. Dendrites are responsible for information transfer in the form of small charged molecules moving rapidly through the cells. The interface between two dendrites is called a synapse. The synapse is the region where electrical signals become chemical signals. If you want to interfere with information transfer in the brain the synapse is one of the places you can do it. This is where many of the commonly used drugs mediate their effects.
STIMULANTS AND INHIBITORS
To regulate all the traffic that occurs between neurons, the brain releases a mix of stimulant and inhibitor molecules. Both types of molecule occur naturally, being made by the brain cells themselves. Stimulants promote signalling between neurons, while inhibitors slow it down. Together stimulants and inhibitors provide a feedback mechanism, so when energy stores in the body are low we attenuate our neural activity accordingly. If you drink a cup of coffee, the caffeine molecule takes the place of adenosine at the ADR, and the signal that normally comes from adenosine that says "slow neural activity" is now missing. This results in a brain without "brakes" as it where and we continue to fire off signals from our neurons despite the need for rest. By ingesting caffeine we have essentially hijacked our own brains and decided to over-ride our own internal feedback mechanisms for determining when we should rest. This is pretty cool in my opinion.
WAIT..I'M CONFUSED
Listen, I don't blame you. In order to discuss this seemingly simple molecule, caffeine, I had to introduce a lot of concepts and terminology. Biology is complicated like that, there are lots of interactions occurring all the time. It is a complicated topic, but here is a summary that should help.
- Caffeine acts a stimulant by preventing the action of adenosine at the adenosine receptor protein.
- This results in a removal of the "brakes" in the brain, and all the stimulatory neurotransmitters in the brain are free to roam around, and stimulate.
- This translates into the physical characteristics we associate with coffee/caffeine, such as increased heart rate, increased reaction time, and increased concentration.
ADDITIONAL READING
- Caffeine Makes Diabetes Worse
- Caffeine and Seasonal Affective Disorder
- Caffeine Blamed for Miscarriages
- Caffeine Pill Could Boost Memory
- Caffeine Could Help Prevent MS
- Drinking Coffee Is Good for Your Heart
- An Interesting Article on the Benefits of Coffee
