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Test Of Nerves

Next time you want to tell people they ‘have some nerve’, show them just how many they have with this cool test. Work out which parts of their body have the most feeling and the therefore the most sensory nerves.

Australian Curriculum links

  • Science > Science as a Human Endeavour > Foundation > ACSHE013
  • Science > Science Inquiry Skills > Foundation > ACSIS011   

You'll need

  • two pencils, pens (with lids on) or skewers
  • ruler
  • pen and paper to record results
  • a person to test

Try this

Safety: Make sure you’re using the pencils and pens gently on the other person’s back.

  1. Holding a pencil in each hand, stand behind the other person.
  2. Holding the pencils about 10 cm apart (use the ruler to measure how far apart 10 cm is if you aren’t sure), gently push on the person’s back using the tips of the pencils.
  3. Ask the person if they can feel one or two pencils.
  4. Record the results.
  5. Repeat steps 2 and 3 with the pencils closer together.
  6. Repeat steps 2 and 3 with the pencils further apart.
  7. Repeat steps 2, 3 and 4 in different areas of the back: upper back, lower back, left and right shoulder blades. Occasionally use just one pencil to see if the other person is cheating!

Further investigation

Record the ‘two-point threshold’ of different parts of the body: finger tip, hand, upper arm, lower leg, foot, etc. Rank the body parts from that with the least number of touch receptors to that with the greatest number of touch receptors.

What's happening?

This activity uses the ‘two-point threshold test’, which measures the sensitivity of a body part by testing how far apart two points need to be before a person feels two points instead of one. Doctors use the ‘two point threshold test’ to test for nerve damage in patients.

Your body is able to feel temperature, pain, pressure and touch because of sensory nerves in the skin. The endings of the sensory nerves in the skin are called touch receptors. When you touch something, your touch receptors collect information about what you’ve touched. This information is sent along the rest of the nerve, to other nerves, to the spinal cord and finally to the brain. The brain then processes the information so that you can tell if what you touched is hot or cold, smooth or rough or even painful.

Touch receptors are not spread evenly across the body. The middle of the back is the least sensitive part of the body to touch because the touch receptors there are few in number and are spread out over a large area. Fingertips are extremely sensitive due to the high number of touch receptors; there are 100 touch receptors per square centimetre on a fingertip!

Further information

The distribution of touch receptors in the human body can be represented by a ‘sensory homunculus’ which is a cartoon drawing of a person with the size of each body part drawn in proportion to the density of touch receptors in that body part. The ‘sensory homunculus’ has enormous hands, fingers, tongue and lips as these are the areas of the body that have the most touch receptors.