Welcome to Your Own Head
In Level 1 we looked at what psychology is and how researchers test their ideas. Now let's look at the hardware all of that runs on: your brain.
A quick reminder before we start. This course is education. It isn't therapy or medical advice. If anything here touches something personal, your GP is a good first place to go.
So here's a question for you. How many cells do you think are doing the thinking right now as you read this?
You may have heard "100 billion." It's close, but a careful 2009 study by Frederico Azevedo and colleagues actually counted, and they found about 86 billion neurons in the adult human brain. That's a lot of tiny messengers. Let's meet one.
Neurons: The Brain's Messengers
A neuron is a nerve cell built to pass on signals. Picture it a bit like a tree with a long trailing root.
The branchy end, made of dendrites, picks up messages from other neurons. Those messages flow into the cell body, the neuron's control centre. If enough of them arrive at once, the neuron "fires." An electrical pulse called an action potential races down the axon, a long cable leading away from the cell body.
Then comes the clever part. Neurons don't actually touch each other. There's a tiny gap between them called a synapse. When the electrical pulse reaches the end of the axon, it can't jump the gap. So the neuron releases chemical messengers called neurotransmitters, and they drift across and attach to the next cell.
So it's electrical inside a neuron and chemical between neurons. Think of a relay race. Each runner sprints their stretch (electrical), then hands the baton across (chemical) to the next runner.
You may have heard of neurotransmitters such as dopamine and serotonin. Each one plays several roles, and we'll meet some of them again later in the course.
The Nervous System: Head Office and the Wiring
Your neurons don't just live in your skull. We split the nervous system into two parts.
The central nervous system is the brain plus the spinal cord. That's head office. The peripheral nervous system is all the nerves running out to your muscles, skin and organs. That's the wiring that carries messages in and out.
Touch a hot pan and signals zip up those nerves, through the spinal cord, and you've pulled your hand away before you've had time to say "ouch."
A Quick Tour of the Brain
Let's take a stroll from the bottom up. Each region does many things, so treat these as one broad job each, a handy label rather than the full story.
The brainstem sits at the base, where the brain meets the spinal cord. It keeps you alive without you having to think about it: breathing, heart rate, sleep and waking.
Tucked at the back is the cerebellum, the "little brain." It helps with balance and smooth, coordinated movement, which is why you can ride a bike without wobbling. Here's a surprise: it holds roughly four out of five of all your neurons.
Deeper inside are some structures you'll hear about a lot. The amygdala helps you spot threats and react emotionally. The hippocampus helps you form new memories. The hypothalamus looks after basics like hunger, thirst and body temperature.
Then there's the big wrinkly outer layer, the cerebral cortex. We divide it into four lobes:
- Frontal lobe (behind your forehead): planning, decisions, self-control and starting movements
- Parietal lobe (top of the head): touch and your sense of where your body is in space
- Temporal lobe (by your ears): hearing and understanding language
- Occipital lobe (at the very back): vision
Yes, you see with the back of your head!
The cortex comes in two halves, or hemispheres, joined by a thick bridge of fibres called the corpus callosum. Keep that bridge in mind. It matters for our second myth.
Myth 1: "You Only Use 10% of Your Brain"
It's a great film plot. Sadly, it's folklore, not science. Why are we so sure?
First, cost. Your brain is only about 2% of your body weight, yet it can use around 20% of your energy. Evolution doesn't usually keep an expensive organ that's 90% idle.
Second, damage. If most of the brain did nothing, injuries to it would often be harmless. In fact, even a small injury in the wrong spot can cause serious problems.
Third, scans. Brain imaging shows activity all over the brain across a normal day. Not every area is busy at every moment, but no region has turned out to be spare.
Myth 2: "Are You Left-Brained or Right-Brained?"
This one has a real kernel of truth, and that's why it sticks.
In the 1960s Roger Sperry studied "split-brain" patients. Their corpus callosum had been cut to treat severe epilepsy. With the bridge gone, the two halves couldn't share information easily, and tests showed they do specialise. For most people, language relies more on the left side. Sperry shared a Nobel Prize in 1981 for this work.
Pop culture stretched that into personality types: logical "left-brainers" and creative "right-brainers." So did that idea hold up?
In 2013, Jared Nielsen and colleagues at the University of Utah analysed brain scans from 1,011 people aged 7 to 29. Yes, some functions lean towards one side. But they found no sign that some people rely on their left-side networks more overall, or their right. In a healthy brain the two halves work together all the time through that bridge.
So being artistic or analytical is a real difference between people. It just isn't about which half of your brain is "in charge."
Something to Notice This Week
Keep an ear out for "brain" claims in adverts, quizzes or chat, like "unlock your hidden potential" or "I'm such a right-brain person." Ask yourself: is that the kernel of truth, or the myth?
Key Takeaways
- Neurons pass signals electrically along the axon and chemically across the synapse, using neurotransmitters.
- The central nervous system is the brain and spinal cord. The peripheral nervous system carries messages to and from the body.
- Brainstem: life support. Cerebellum: balance and coordination. Amygdala: threat and emotion. Hippocampus: new memories. Hypothalamus: basic body needs.
- Lobes: frontal (planning), parietal (touch), temporal (hearing and language), occipital (vision).
- We use virtually all of our brain. Energy cost, injury evidence and scans all count against the 10% myth.
- Some functions lean to one side, but people aren't "left-brained" or "right-brained."