The brain: parts, jobs and reaction time
The cerebrum, cerebellum and brain stem, two hemispheres and four lobes, the nervous system and neurons. With a reaction-time fair test.
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An adult brain weighs about three pounds (about 1.4 kg). It sits in the skull, washed by a protective fluid.[1]
The cerebrum is the biggest part: it is where conscious thoughts and actions come from, and it holds memories. The cerebellum coordinates movements, including learned ones like playing the piano. The brain stem helps control vital jobs such as breathing and heart rate.[1]
The cerebrum has two halves (hemispheres) joined by the corpus callosum. Surprisingly, the right hemisphere mainly controls the left side of the body, and the left controls the right.[1]
Each hemisphere has four lobes. The frontal lobe helps with planning and reasoning and controls voluntary movement; the parietal lobe deals with touch and temperature; the temporal lobe with hearing and memories; the occipital lobe with images from the eyes.[1]
The brain and spinal cord form the central nervous system; the nerves that reach the rest of the body form the peripheral nervous system. Together they detect stimuli (sensation), process the information (integration) and make muscles or glands act (response).[2]
Nerve cells are called neurons. Each has a cell body, dendrites that receive messages and an axon that sends them on. A fatty coat called myelin helps signals travel faster and farther.[1]
Try it: Reaction time: is your writing hand quicker?
You need
- A 30 cm ruler per pair
- Results table
- The conversion chart below (distance → time)
Safety
Drop the ruler straight down from a small height and keep faces clear. Use a plastic or wooden ruler without sharp edges. No grabbing at each other.
What to do
- Question: is your reaction time quicker with your writing hand than with your other hand? Write a prediction.
- The holder holds the ruler at the top (30 cm end up). The catcher puts thumb and first finger at the 0 mark, open, not touching.
- The holder says 'ready' and then drops the ruler some time in the next 5 seconds, at a different moment each time so the catcher cannot guess.
- Record the cm mark at the top of the catcher's fingers. Do 5 tries with the writing hand and 5 with the other hand. Work out the mean for each.
- Fair test: same ruler, same holder, same starting position, same seat. Change only the hand. Use the chart to turn your means into seconds: about 2.5 cm ≈ 0.07 s, 15 cm ≈ 0.18 s, 30 cm ≈ 0.25 s.
What happens, and why?
Catching the ruler is not a reflex. Your eyes see the ruler move, the signal goes to the brain (to the part that handles images, then to the part that controls movement), down the spinal cord and out along nerves to the hand muscles. That chain takes a fraction of a second, and the further the ruler falls, the longer it took. Many people find their writing hand a little quicker, but practice and attention matter too.[7][8]
Play: Which part of the brain?
Which part of the brain is most linked with each job?
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Quiz
Other ages: Ages 6–7 · Ages 15–16