Introduction to Drugs and the Nervous System

In the previous chapters, we looked at how the nervous system sends electrical impulses to keep us coordinated. But what happens when we introduce outside chemicals into this delicate system? In this chapter, we will explore drugs and alcohol, looking at how they change the way our brain and body function, and why some can be very dangerous.

Note: This chapter is part of the "Coordination and response" section. It links closely to what you learned about neurones and synapses!

What is a Drug?

A drug is any substance taken into the body that modifies or affects chemical reactions in the body. Some drugs are used in medicine to help us get better, while others are used recreationally because of the effect they have on the mind.

Legal vs. Illegal Drugs

Drugs are generally categorized into two groups based on the law:

  • Legal drugs: These include medicines like paracetamol and antibiotics, as well as social drugs like alcohol, caffeine, and nicotine (found in tobacco).
  • Illegal drugs: These are substances that are against the law to possess or sell because they are considered highly dangerous or addictive. The main examples you need to know are heroin, cannabis, and cocaine.

The Dangers of Illegal Drugs

Illegal drugs can have devastating effects on the nervous system and overall health. Here is a breakdown of the drugs named in your syllabus:

1. Heroin

Heroin is a powerful depressant. This means it slows down the functions of the central nervous system. It can cause a feeling of euphoria, but it is highly addictive. Users often develop a "tolerance," meaning they need more of the drug to get the same effect, which can lead to a fatal overdose. Because it is often injected, there is also a high risk of contracting infections like HIV if needles are shared.

2. Cocaine

Cocaine is a stimulant. Unlike a depressant, a stimulant speeds up the nervous system. It makes the user feel intensely alert and energetic. However, it puts massive strain on the heart and can lead to severe mental health issues and permanent damage to the nervous system.

3. Cannabis

Cannabis is a drug that affects how a person perceives the world. It can cause relaxation but also leads to increased heart rate and memory loss. Long-term use is linked to an increased risk of developing mental illnesses like schizophrenia.

Quick Tip: Remember that depressants slow you down (like a "down" button) and stimulants speed you up (like an "accelerator").

Common Painkillers: Paracetamol

We use painkillers to treat symptoms of illness or injury. Paracetamol is one of the most common legal painkillers. It works by affecting the chemical messengers in the brain that tell us we are in pain. It is very effective at reducing fever and mild-to-moderate pain, but it must be taken in the correct dosage; taking too much can cause permanent liver damage.

Alcohol and the Nervous System

Alcohol is a very common legal drug, but it is also a depressant that has a major impact on the nervous system.

Short-term effects on the Nervous System:

  • Slowed Reaction Times: Alcohol slows down the speed at which nerve impulses travel. This is why "drink-driving" is so dangerous—the brain takes longer to process information and tell the muscles to hit the brakes.
  • Loss of Coordination: It affects the cerebellum (the part of the brain responsible for balance), leading to stumbling or slurred speech.
  • Reduced Inhibitions: Alcohol affects the cerebral hemispheres, making people more likely to take risks or act aggressively.

Long-term effects and Behavioural Consequences:

Long-term drinking can lead to alcoholism, where a person becomes physically and mentally dependent on the drug. Behavioural consequences include:

  • Increased aggression and violence.
  • Breakdown of personal relationships and loss of employment.
  • Severe memory loss and permanent brain damage.

The Role of the Liver

The liver is the primary organ responsible for detoxification. This means it breaks down poisonous substances, including alcohol, into harmless products that can be removed from the body.

Liver Damage

While the liver is good at its job, it can only process a small amount of alcohol at a time. If a person drinks heavily over many years, the liver cells are overworked and die. This leads to a condition called cirrhosis, where healthy liver tissue is replaced by useless scar tissue. Eventually, the liver may fail completely, which is fatal.

Did you know? Because the liver is responsible for regulating blood sugar and forming urea (as you learned in the Homeostasis chapter), liver damage from alcohol affects almost every other system in your body!

Quick Review Box

Key Takeaways:

  • A drug is a substance that changes chemical reactions in the body.
  • Heroin (depressant), Cocaine (stimulant), and Cannabis are dangerous illegal drugs.
  • Alcohol is a depressant that slows reaction times and causes long-term damage to the brain and liver.
  • The liver detoxifies alcohol, but excessive drinking causes cirrhosis.
  • Paracetamol is a legal painkiller used to block pain signals in the nervous system.

Common Mistake to Avoid: Students often think alcohol is a stimulant because it makes people loud or "energetic" at parties. In biology, alcohol is always a depressant because it slows down the speed of the nervous system.