Teacher sheet · Ages 15–16 · about 45–50 minutes
Sensory receptors: transduction, receptive fields and thresholds
Lesson page: echoesof.science/school/senses/ages-15-16/ · Pupil worksheet: echoesof.science/school/senses/ages-15-16/print/
Learning aims
- Classify receptors by structure, location and stimulus.
- Explain transduction and slow and rapid adaptation.
- Link two-point thresholds to receptor density and receptive fields.
- Describe taste transduction, olfactory coding and cochlear frequency mapping.
- Collect repeated measurements and express them as mean ± uncertainty.
Lesson plan
| Time | Activity |
|---|---|
| 5 min | Starter: put on a watch or bracelet. Why do you stop feeling it after a while? |
| 10 min | Read the text; build a receptor classification table. |
| 20 min | Two-point threshold investigation. |
| 5 min | Calculate means, uncertainties and the forearm ÷ fingertip ratio. |
| 5 min | Quiz or the touch receptor game. |
Materials for the experiment
- A paper clip bent into a U with blunt, rounded ends (or a two-point caliper from the lab)
- A ruler with mm markings
- Results table
- Calculator
Safety: Use blunt, rounded ends only and light pressure; never break or scratch the skin. Do not test near the eyes or on the face. Test only healthy, intact skin, and only on someone who has agreed; anyone may stop at any time.
Common misconceptions
| Pupils may think… | Actually… |
|---|---|
| Each sense has just one kind of receptor. | Touch alone uses several mechanoreceptors tuned to different stimuli and frequencies. |
| Two-point sensitivity depends only on how many receptors there are. | Receptive field size, and how receptors connect to central neurons, matter too. |
| The tongue has separate zones for each taste. | Taste cells for each quality are spread across the tongue. |
Worksheet answers
- Structure: encapsulated ending; location: exteroceptor in the skin; stimulus: mechanoreceptor (deep pressure, high-frequency vibration).
- Fingertip receptors have small receptive fields and high density, so two close points stimulate receptors that signal to different central neurons; on the forearm fields are large, so points far apart still feel like one.
- Answers depend on data; compare mean ± uncertainty with about 2–3 mm and 35–40 mm, and the ratio with roughly 12–20.
- Chewing releases aromas that reach the smell receptors through the channel from the roof of the throat to the nose; a cold blocks this, so only the basic tastes are left.
Quiz answers
- Which receptor responds to deep pressure and high-frequency vibration (around 250 Hz)? Pacinian corpuscle. Pacinian corpuscles detect deep pressure and high-frequency vibration.[1]
- Which tastes are triggered directly by ions? Salty and sour. Na⁺ triggers salty and H⁺ triggers sour; the others use G protein–coupled receptors.[1]
- A receptor keeps firing while a pressure stays constant. It is… slowly adapting. Slowly adapting receptors keep firing during a constant stimulus.[4]
- What makes smell different from the other senses? It reaches the cortex without first synapsing in the thalamus. Smell bypasses the thalamus and links to the limbic system.[1]
- A 20 kHz tone mainly activates hair cells… at the base of the cochlea. High frequencies activate the base, low frequencies the apex.[1]
- Thresholds: forearm 38 mm, fingertip 2.5 mm. The forearm threshold is about… 15 times larger. 38 ÷ 2.5 ≈ 15.[4]
Going further
Design a test of adaptation: rest a coin on the back of the hand. How long until it can no longer be felt? Which receptor type would explain this?
Sources used in this lesson
- [1] Anatomy and Physiology, 14.1 Sensory Perception (OpenStax, Rice University): reliability High
- [2] Taste Disorders (National Institute on Deafness and Other Communication Disorders (NIH, USA)): reliability High
- [3] Smell Disorders (National Institute on Deafness and Other Communication Disorders (NIH, USA)): reliability High
- [4] Our Sense of Touch: Two-Point Discrimination (Neuroscience for Kids, University of Washington): reliability Medium-high
Full list with links and a note on each source's reliability: echoesof.science/school/senses/sources/
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