Experiment: Reflex Arcs – Responding to Stimuli
Introduction
Reaction time is a measure of how quickly an organism can respond to a particular stimulus. The
model for information flow within an organism can be represented in this way:
Stimulus > Receptor > Integrator > Effector > Response
More specifically, in vertebrates, information flow can be represented in this way:
Stimulus > Sensory Neuron > Spinal Cord or Brain > Motor Neuron > Response
Objective
In this experiment, you will measure your reaction time by catching a metric ruler with your fingers.
After you catch the ruler, you will convert your measurement in centimetres into a reaction time
measured in seconds.
Procedure
Part A
1. Sit in a chair with your arm resting on a table so that your wrist hangs off the edge. Your
friend should hold the ruler so that it dangles above your hand. Make sure the "zero" end of
the ruler is hanging between your thumb and finger.
2. When your friend lets go of the ruler, try to catch it between your thumb and finger as quickly
as you can.
3. Record your first measurement in the table provided and calculate the time in seconds using
the equation
2𝑦
𝑡= √
𝐺
𝑦 = the distance you measured in centimeters
𝐺 = the acceleration due to gravity constant (980 cm/sec2 )
𝑡 = time in seconds
4. Repeat for trial #2 and trial #3.
5. Calculate the average reaction time and record in the data table.
6. Record your friends data and calculate their average in the table also.
Part B
7. Draw a bar graph to present your data. Along the left side of the graph (Y-axis) write the times
from the reaction time chart. Across the bottom of the graph (X-axis) write the names of
yourself and your volunteers separate columns. Draw a bar for each person up to the number
that matches their average reaction time in seconds.
8. Who has the best reaction time?
Experiment: Reflex Arcs – Responding to Stimuli
Results
Name
Trial #1
(cm)
Time (s)
Trial #2
Ruler
Time (s)
(cm)
Trial #3
Ruler
Time (s)
(cm)
Did your reaction times vary a lot or were they pretty much the same from trial to trial?
Conclusion
Write your own conclusion for the experiment
Average
Time (s)