Many of us consume caffeine every morning and sometimes multiple times throughout the day. We do it for that caffeine “high” that makes us feel alert and awake. But how exactly does caffeine interact with our brain and body to make us feel that way?
Caffeine is a central nervous system stimulant and is generally considered to be the most widely consumed psychoactive drug. A psychoactive drug is anything that alters the normal functions of the nervous system and creates alterations in mood, perception, cognition or consciousness.
The main way caffeine alters our brain and nervous system is by attaching to the adenosine receptors on our neurons, or brain cells. The molecular structure of caffeine is similar enough to the structure of adenosine that it gets mistaken for adenosine and is then allowed to bind to the receptors, leaving no room for adenosine molecules to attach.
This is one aspect of how caffeine promotes wakefulness. Adenosine is an organic compound found in the brain. It accumulates and attaches to receptors throughout the day, eventually making you feel sleepy because adenosine suppresses and slows nerve cell activity. Adenosine concentration then decreases during sleep. When you consume caffeine, the adenosine has nowhere to attach and decreases feelings of drowsiness. This is one reason why consuming caffeine late in the day makes it hard to fall asleep. It is essentially delaying one aspect of your sleep and wake cycle.
When caffeine binds to adenosine receptors, it causes cell activity to speed up instead of slowing down. This increased neuron activity alerts the pituitary gland and makes it think something urgent is happening. In response, the pituitary gland releases adrenaline, which is your “fight or flight” hormone.
The release of adrenaline does various things to the body, including increasing your heart rate, dilating the pupils, opening the airway, increasing blood flow to the muscles, raising blood pressure, slowing blood flow to the stomach, and tensing the muscles. These physiological symptoms make you feel excited and sometimes anxious after consuming caffeine.
The brain will respond to long-term caffeine use by increasing the amount of adenosine receptors so the molecule has somewhere to attach. The increase in receptors thus requires more caffeine to create the same sensation of wakefulness, thus increasing your tolerance to caffeine. These additional receptors also contribute to the withdrawal symptoms of increased drowsiness when you try to quit or decrease caffeine consumption. Luckily, this artificial inflation in the number of adenosine receptors will naturally correct itself after about a week or so of no caffeine.
Caffeine also increases the amount of dopamine because it prevents its reabsorption in the brain. This is similar to how cocaine affects the brain, but to a much lesser degree. The dopamine rush caffeine provides is also a contributing factor of caffeine’s mild addictiveness.
The half-life of caffeine, or the time it takes caffeine to lose one-half its potency once ingested, is estimated to be about six hours. That means if you drink a standard cup of coffee that contains around 150 milligrams of caffeine, you will still have about 75 milligrams of caffeine in your body about six hours later.
As the amount of caffeine decreases, receptors open up for adenosine and the drowsiness will likely return. You’ll feel the urge to go for another cup, but just remember that next dose of caffeine will boot out the adenosine you may wish you had when you’re trying to go to sleep later that day. To avoid this, try to stop consuming caffeine by the middle of your day.
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