Caffeine is a naturally occurring stimulant found in coffee beans, tea leaves, and cocoa pods. It acts as a central nervous system stimulant by blocking adenosine receptors in the brain, which increases alertness. Caffeine enters the bloodstream quickly and remains there for several hours, stimulating neural activity and reducing fatigue and drowsiness. However, regular high consumption of caffeine can lead to physical dependence and withdrawal symptoms like headaches when caffeine intake is reduced.

1. Caffeine

2. Caffeine in food
• Natural sources of caffeine
include coffee beans, tea
leaves, kola nuts, guarana
berries and cacao pods.
• Caffeine is most well
known for being a natural
component of chocolate,
coffee and tea.
• It is also added to colas
and energy drinks.
• Around 90 percent of
Americans consume
caffeine every single day in
one form or another.

3. Cell Signalling
• To understand a “caffeine jolt” we must first understand the
pathways which the body’s cells respond to certain signals in their
environment. There are three sequential processes involved in the
cell’s response to any signal.
1) The signal binds to a receptor protein.
2) The binding of the signal causes a message to be conveyed to
the cell’s cytoplasm and amplified.
3) The cell changes its activity in response to the signal

4. Caffeine as a drug
• Caffeine is chemically known as 1,3,7-trimethylxanthine.
• It is an odourless white crystalline powder that has the ability to stimulate
the central nervous system.
• Caffeine enters the bloodstream through the stomach and small intestine,
causing its effects in just 15 minutes after consumption. It stays in the body
for quite a long time with a half-life of around 6 hours.
• Caffeine has a similar structure to adenosine, which is a naturally occurring
neurotransmitter in the brain, so it occupies the adenosine receptors and
inhibits brain cell function so alertness is restored.
• The role of adenosine is to suppress neural activity in the brain, increase
blood flow throughout the body and contribute towards energy metabolism.

5. Effects of Caffeine on the
Nervous System
By suppressing these actions of adenosine, caffeine has the following
effects:
• It increases neural activity in the brain - leading to a temporary
increase in mental alertness and thought processing swell as
reducing drowsiness and fatigue.
• It decreases energy metabolism in the body- (after long-term
consumption) leads to adrenal fatigue.
• It reduces blood flow to the brain- leading to headaches,
dizziness and reduced fine motor coordination.
Other nervous system effects of caffeine include:
• Increased heart rate
• Increased thirst and hunger
• Anxiety and nervousness
• Dilation of air passages
• Insomnia
• Release of glucose from liver

6. In more detail..
•Caffeine inhibits the action of an enzyme, (phosphodiesterase), resulting in an
increased intracellular concentration of -(cyclic AMP)- in the axon.
•This can result in the release of increased amounts of excitatory transmitter
substances in the brain and has a mild stimulatory effect, increasing alertness.
•Simply, caffeine causes more transmitters to be released, which will in turn cause
ions to move in and out of the post-synaptic neurone, making it depolarised
(more positive inside the axon than the outside).

7. Caffeine Dependence
• Some studies show that caffeine causes physical dependence.
• One way to tell if someone is dependent is to remove caffeine from
their diet and see if they have any withdrawal symptoms.
• Withdrawal symptoms include headache, fatigue and muscle pain
within 24 hours after the last dose of caffeine.
• One study has stated that the minimum consumption of caffeine for
physical dependence is 4 cups of coffee per day.
• Caffeine can be lethal at dosages over 10g for the average adult.
This is equivalent to drinking at least 80 cups of coffee in quick
succession.