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Reaction time

Test your reaction time. Understand the path of the neurons to carry out this task.
Science content (2016 curriculum): 
Biology: Sensing, Organ Systems (4, 5, 6)
Science topic (2005 curriculum connection): 
Life Science: Characteristics of Living Things (grade K)
Life Science: Needs of Living Things (grade 1)
Life Science: Animal Growth and Changes (grade 2)
Life Science: Human Body (grade 5)
Lessons activity is in: 
  • a table
  • a ruler
  • a partner

Rest your arm on the edge of a table or chair, with your hand hanging over the edge (this prevents you from dropping your hand down to match the yardstick's motion). Hold your thumb and index finger a couple of cm apart.
Have a friend hold a ruler so that the zero mark is just between your two fingers.
Without warning, have your friend drop the ruler. Close your fingers on the stick to stop it as quickly as you can.
Read off the number where you grabbed it (if you were able!).
Try a few times and record your fastest time.

What is happening in your brain during this activity:
Show image of pathway, then trace pathway on a real brain if possible: the eye sees the ruler drop and a message is sent along a neuron to the thalamus in the centre of the brain, from which another neuron sends a message to the visual cortex. Once the image of the ruler dropping is perceived, there is a signal to close the fingers, down one neuron from the motor cortex to the spinal cord. Then a second neuron all the way from the spinal cord down the arm to the finger muscle. Then the finger muscle contracts.
All this takes milliseconds. The slowest part is the message passing between neurons; the neurons themselves transmit the electric message very fast.

Hockey goalies, and other people in high-speed sports need to have very fast reaction times. They would be able to catch the ruler at about 11cm, giving a reaction time of 0.15 seconds. Some students might have reaction times this fast, but most will fall between 15cm and 20cm (reaction times from 0.18 - 0.2 seconds).

This activity was adapted from:

Grades tested: 
Gr 4
Gr 5
Paul An
Teaching site: 
Carnarvon Elementary
ingridscience afterschool
ProD for Elementary teachers