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Homunculus and Dermatome Map

Run the Homunculus and Dermatome Map MicroSim Fullscreen

About This MicroSim

This MicroSim links two body maps that doctors use every day. The left panel is a front view of a person with clickable dots on 11 body regions. The right panel is a front-view (coronal) slice of one brain hemisphere. Its outer edge shows the primary somatosensory cortex (S1) on the postcentral gyrus as a strip of body-part segments, running from the toes and foot on the inner (medial) wall, over the top of the brain, and down the side to the face, lips, tongue, and throat. Segment sizes are exaggerated for the hands and lips, like the classic sensory homunculus.

When you pick a region, the sim highlights its segment on the opposite hemisphere and gives the spinal level that carries touch from that spot, using the standard ISNCSCI key sensory points (for example C6 for the thumb and T10 for the belly button). The lips have no spinal dermatome; they are supplied by the trigeminal nerve (cranial nerve V).

Two honest caveats are built in. Dermatome maps differ between textbooks and between people, so the levels are standard test spots, not exact borders. The cortex segment sizes are illustrative, not measurements.

How to Use

  1. Click any blue dot on the body, or choose a region and side from the dropdown menus.
  2. Look at the right panel. The title tells you which hemisphere you are seeing, and the orange segment shows where that body region is represented.
  3. Read the box at the bottom for the cortex location, the dermatome level (or nerve), and the key test spot.
  4. Switch between the person's right and left side and watch the brain slice flip to the other hemisphere.
  5. Press Quiz me. A gold dot marks a body region. Click the matching segment of the cortex strip. You get two tries, and your first-try score is shown at the bottom right.
  6. Uncheck Show labels to quiz yourself without the segment names.

Learning Objective

Students will be able to locate where a touched body region is represented on the opposite primary somatosensory cortex and name the spinal level (dermatome) or cranial nerve that carries it.

Bloom's Taxonomy Level: Apply

Iframe Embed Code

Place the following line in your website to include this MicroSim in your course.

<iframe src="https://aaryavvatts-lab.github.io/neuroscience-textbook/sims/ch06-homunculus-dermatomes/main.html" height="752px" width="100%" scrolling="no"></iframe>

Lesson Plan

Grade level: 9 to 12 (also suitable for Brain Bee preparation)

Duration: 20 to 25 minutes

Prerequisites: basic brain anatomy (lobes, central sulcus, postcentral gyrus) and the idea that sensory pathways cross to the opposite side.

Activity:

  1. Predict (3 min). Before opening the sim, students sketch where they think the thumb, lips, and foot are represented on the postcentral gyrus, and guess which body part gets the most cortex.
  2. Explore (8 min). In pairs, students click all 11 regions on one side and record each region's cortex segment and dermatome level in a table. They then click the same regions on the other side and note what changes and what stays the same.
  3. Explain (5 min). Pairs answer: Why do the lips and thumb get large segments? Why does the slice flip when you switch sides? Why do the lips have no spinal level?
  4. Quiz (5 min). Each student uses Quiz me with labels turned off and reports a first-try score out of 10.

Assessment questions:

  1. A patient feels numbness on the back of the little finger only. Which spinal level is most likely involved, and which hemisphere would receive touch from that finger if it were on the patient's right hand?
  2. The foot area is on the inner (medial) wall of the hemisphere. Predict what kind of sensory loss a small injury to the top of the brain near the midline might cause.
  3. Two textbooks put the front of the knee in different dermatomes. Explain why this does not make dermatome testing useless.

This MicroSim is used in Chapter 6: Hearing, Touch, Taste, Smell, and Pain.