Unit 11, lesson 55. About 12 minutes.

Electricity in your body

How does a message get from your toe to your brain so quickly?

Play

Getting the experiment ready…

Explain

Your body uses tiny electric signals.

They run along your nerves.

Your body has its own electricity. Tiny signals travel along nerves and carry messages.

When you touch something hot, a signal rushes to your spinal cord and back, and your hand jumps away.

Your heart has an electric rhythm too. It tells the heart muscle when to beat.

Nerve signals are waves of charged atoms, called ions, moving through cell walls. They are much slower than current in a wire.

t = d / v. The fastest nerves carry signals at about 100 m/s, and some pain nerves about 1 m/s.

Worked example: a signal travels 1.5 m at 60 m/s. So t = 1.5 / 60 = 0.025 s.

You stub your toe
A signal races up a nerve
Your brain says ouch

Want the full story?

Heart doctors record its electrical signals in an ECG, and a pacemaker can correct a faulty rhythm. Your body runs on very small voltages, about a tenth of a volt across a nerve cell. Mains electricity is very dangerous, as it can upset these signals.

The Formula

time = distance ÷ signal speed

t = \frac{d}{v}

$t$: the time for the signal, measured in seconds (s)
$d$: the length of the nerve, measured in metres (m)
$v$: the signal speed, measured in metres per second (m/s)

Try the numbers

Nerve length: 1.5 mSignal speed: 60 m/s

Time taken: 0.03 s

Try it at home

You need a friend, a ruler.

You need: a friend, a ruler.

Try to catch a falling ruler.

A friend holds a ruler above your open hand.
They drop it with no warning.
Catch it, and read how far it fell.

What's happening: the signal has to go from your eyes to your brain, and on to your hand, which takes about 0.2 s.

Physics is life

Your body

Your heart has an electric beat.

A special patch of your heart sets off every beat with a tiny electric signal.

Daily life

Doctors read your heartbeat.

Doctors use ECG machines to read the electrical signals of the heart.

Nature

Sharks sense tiny electricity.

Sharks can detect the tiny electric signals made by the muscles of their prey.

Space

Astronauts' hearts are watched too.

Doctors monitor astronauts' heartbeats from Earth.

Quick check

Question 1 of 3

What are nerves for?

Words to know

Nerve: A body cell or bundle that carries electrical signals.

Nerve: A body cell or bundle that carries electrical signals.
Current: The flow of electric charge. It is measured in amps.
Electric charge: A property of tiny particles that makes them attract or repel.

Next up

The electromagnetic spectrum