This week we investigated a type of cell called the sensory receptor. These receptors are found in our skin and allow us to feel pressure, pain, heat, and cold. The kids made pressure probes (see photo), which were used to test 4 different areas of the body: fingertip, forearm, cheek, and calf. The idea was to GENTLY poke these areas with the probe, gradually decreasing the distance between the 2 toothpicks until the subject could only feel 1 prick. The area with the smallest 2-point discrimination was the area that was most sensitive and was assumed to contain the highest number of sensory receptors for pressure. The kids were surprised to find quite a great deal of variation. Subjects could distinguish 2 distinct pricks at an average of 2.5 mm on their fingertips, while the 2-point discrimination was much larger for the calf and forearm - as much as 7 mm.
We concluded by discussing why it might be adaptive for some areas to be more sensitive than others.