Beacon Lesson Plan Library

Self Portrait, What Nerve!

Beverly Grim


Students determine the density of touch receptors in various parts of the right-hand side of the human body. By using the data collected, students draw a picture of the -Homunculus- of the experimental subject.


The student knows that organisms respond to internal and external stimuli.

Creates potential solutions to industry problems using math and/or scientific concepts and communicates solution using industry appropriate language arts and graphic skills.

Demonstrates the ability to cooperatively work in various settings, across diverse populations.


-Round toothpicks
-Glue sticks
-Adhesive tape
-Tag board (made from a file folder or 5 by 7 index cards)
-Graph paper
-Templates (see associated file).


1. Prepare students for lesson:
-Discuss nerves and nerve cells.
-Discuss nerver receptors and receptor sites.
-Discuss the brain and regiospecificity.
-Demonstrate reflex and nerve response.

2. Collect materials.


The students will:

-know that nerve cells relieve stimuli and send impulses to the brain to be interpreted
-know that organisms respond to internal and external stimuli
-know that the concentration of nerve cells varies in different parts of the body
-know that the Homunculus is an area of interpretation within the brain
-demonstrate a technique for determining nerve density
-understand that nerve density and activity may be measured

1. Inform students that they will construct a Receptor Touch Measuring Tool.

Follow these instructions.

(a) Cut out the following measuring tool template and glue it to tag board, poster board or card board. See associated file: Measuring Tool Template. This template is drawn to scale.

(b) Place a weight on top, such as a book, and wait a minute for it to dry.

(c) Cut out the six pieces. Cut the lettered sections along all the lines making six pieces, A-F.

(d) Assemble the base. Glue B and C on top of A, leaving space in the middle for F (see figure 1: finished tool)

(e) Assemble the top. Glue D and E to B and C only, leaving the center spaces under D and E open.

(f) Assemble the tool. After the glue has dried, slide F under D and E so that it is parallel with B and C but free to slide back and forth.

(g) Attach toothpicks. Using adhesive tape, tape one toothpick along the far edge of D, with its top reaching only as high as the top of D. This will be the fixed point. Be sure the tape does not prevent F from sliding (see associated file: finished tool). Continue by taping a second toothpick to the inside edge of the perpendicular arm of F. Be certain that the points of the toothpicks are aligned. See associated file, finished tool.

2. Prepare student groups. A group of students will consist of an experimental subject who is blindfolded and an experimental recorder. Starting from the head and working down to the feet, inform students that they will measure the distance between touch receptor fields in specific parts of the right-hand side of the body. Data will be entered into the data table See figure two: sensitivity data table)

3. Outline the following procedure for measuring distance:
(a) Choose an area from the data table. See associated file: Sensitivity Data Table.

(b) Spread the toothpicks apart and press the points lightly on the skin of the subject. The subject may detect two points of contact. If he feels only one, move the toothpicks further apart and repeat the the process . Once the subject feels two points, move the toothpicks closer together, 0.5 cm at a time, until the subject no longer is able to distinguish two separate points.

(c) Measure the distance between the toothpicks in centimeters. Repeat this measurement two times in the same general area and record the mean (average) in the data table.

(d) Continue this process for the other body areas listed in associated file: Sensitivity data table.

(e) Change toothpicks when a new subject is to be used.

3. Have students complete mathematics calculations. Follow these instructions:

The number recorded for each body part represents the distance between each sensory receptor field, so the distance measured is inversely proportional to the cortical area dedicated to that body part. That is, the closer the receptor fields, the larger the area on the cortex. To calculate the inverse, divide each mean into the number 1. For example, if the distance equals 0.25, then divide 1 by 0.25 which equals 4. Calculate the inverse for each body part and record it on the data sheet.

4. Have students prepare a drawing based on their data and calculations. Follow these instructions:

Using graph paper, draw a proportional picture of the -Homunculus.- If the inverse is 4, then the body part occupies 4 boxes on the graph paper. To enlarge the scale, multiply all the values by an enlarging factor such as 10. If the inverse was 4, multiplying by 10 enlarges the body part to 40 boxes.

5. Analyze representations.


Assessment of this lab activity may be done using the following criteria:
-successfully followed directions
-successfully measured 3 data points and is able to determine mean.
-completed data table
-accurate inverse values
-accurate calculations for enhancing factors
-accurate box counts and correct representation

The following questions may be used to assess student understanding of this material:

1. Based on this lab activity, what may be said about nerve cell density:
a. It varies to body location.
b. It is the same regardless of location.
c. It can not be measured.
d. It can not be used to understand advanced relationships.

(answer a. Nerve receptors are more dense in sensitive areas of the body.)

2. Based on this activity, what statement is obviously true?
a. Organisms do not respond to external stimuli.
b. Response to external stimuli can not be measured.
c. Organisms respond to external stimuli.
d. Response to external stimuli is the same for all parts of the body.

(answer c. Organisms respond to external stimuli and the response can be measured.)

3. Based on this activity, what can be said about nerve density?
a. Sensitive areas of the body have a great distance between receptors.
b. All locations of the body are equally sensitive.
c. Sensitive areas of the body have a small distance between receptors.
d. The sensitivity of the body can not be measured.

(answer c. Sensitive areas of the body have a dense nerve count and nerve receptors are very close.)

Various areas of the body have different nerve density. More sensitive areas have greater density. Less sensitive areas have less density. The density of the the nerve receptors can be measured by the effect of external stimuli. The density can be measured and information about our nervous system may be determined from analysis of the results.


Have students answer the following questions.
1. Which side of the brainís sensory cortex did you map? Explain. Remember that the right hand side is mapped by the left brainís sensory cortex.)
2. How does your groupís Homunculus compare with those drawn by other groups? Discuss the similarities and differences. Students should notice that the tongue, fingers, and feet are more sensitive. Because there are more receptors, the body regions will map out a greater surface area.
3. Is there any adaptive or evolutionary value to the amount of space dedicated to each body part? Explain.

Attached Files

The worksheets needed to complete the lesson.     File Extension: pdf

Return to the Beacon Lesson Plan Library.