TouchFollow the signal

Skin. Signals. Sensation.

Follow the signal.

1. Detect a pattern

Labeled general skin schematic showing superficial and deeper sensory structures, including Merkel, Meissner, Pacinian and Ruffini receptors.Open larger labeled diagram ↗
General skin schematic. BruceBlaus / Blausen.com staff, 2014. Source · CC BY 3.0. No crop.
Merkel / SA-I
Held indentation and fine detail
Meissner / RA-I
Changing contact and flutter
Pacinian / RA-II
High-frequency vibration
Ruffini / SA-II
Skin stretch; traditional anatomical pairing

Four classic tactile afferent types in hairless skin. Slowly adapting responses can continue during a held stimulus. Rapidly adapting responses emphasize change.

Dougherty, 2020; Paré et al., 2003

Held stimulusSARA
Held stimulus
SA
RA
Conceptual response sketches, not measured traces.

2. Convert force into a signal

Force01

Skin deforms

Na⁺02

Mechanically gated channels open

Local voltage03

Net positive current changes local voltage

Spikes04

Threshold triggers action potentials

Step 1 of 4

PIEZO2 is a major touch channel. A graded local voltage change can start all-or-none traveling spikes.

Dougherty, 2020; Chesler et al., 2016

3. Follow the main routes

BODY SIDESRIGHTLEFTCortex / thalamusMedullaSpinal cordRight-hand inputMedulla crossingSpinal crossing

Right / left = body sides

Fine touch / vibration

RIGHTLEFTThalamus / cortexMedullaSpinal cordRight-hand input

Pain / temperature

RIGHTLEFTThalamus / cortexMedullaSpinal cordRight-hand input
Fine touch / vibration
Crosses in the medulla
Pain / temperature
Crosses in the spinal cord

These are two major pathways from the body. They relay toward the thalamus and sensory cortex.

Dougherty, 2026

4. Compare temperature and pain

Fresh mint leaves on a white surface
Ruby Sengar / Pexels. Photo · Pexels license.
AδC
Aδ
C
TRPM8
Cold and menthol
TRPV1
Noxious heat and capsaicin
Aδ nociceptors
Thinly myelinated; typically faster, sharper
C nociceptors
Unmyelinated; typically slower, burning or aching

Warmth depends on activity across neurons. Nociception processes potentially harmful stimulation. Pain is the personal experience.

McKemy et al., 2002; Caterina et al., 1997; Paricio-Montesinos et al., 2020; Dubin & Patapoutian, 2010; IASP, 2020

5. Notice what can change

Descending controlInputSpinalcircuitsOnwardTouch input / inhibitory circuitryTransmission can change
Descending controlInputSpinalcircuitsOnwardTouch input /inhibitory circuitry

Transmission can change

Gate control
Touch input can recruit inhibitory spinal circuits.
Endorphins
Opioid receptor signaling can reduce transmitter release and excitability.
Descending control
Brain signals can inhibit or facilitate transmission.
Phantom sensation
A sensation can be located in an absent limb.

Phantom sensations may be painless. Phantom pain is felt in the absent limb; residual-limb pain is in remaining tissue. Peripheral, spinal, and brain processes can interact.

Mendell, 2014; Che & Roth, 2023; Heinricher et al., 2009; Hanyu-Deutmeyer et al., 2023

6. Try tap, hold, glide

TapHoldGlide
Tap
Hold
Glide
Optional hold timer20 seconds
  1. Tap your opposite palm gently
  2. Hold comfortable contact for 20 seconds
  3. Glide a fingertip a short distance

Notice contact starting, maintained pressure, and movement. Observe instead if you prefer. Use light contact on intact skin. This does not test individual receptors.

Which felt most obviously changing? Could you still sense the held contact?

Dougherty, 2020

Full APA references and image credits

Download APA references PDF ↗
  1. Dougherty, P. (2020, October 7). Chapter 2: Somatosensory systems (C. Tsuchitani, content contributor). In Neuroscience online. McGovern Medical School at UTHealth Houston. https://nba.uth.tmc.edu/neuroscience/m/s2/chapter02.html Open source
  2. Dougherty, P. (2026, July 7). Chapter 4: Somatosensory pathways (C. Tsuchitani, content contributor). In Neuroscience online. McGovern Medical School at UTHealth Houston. https://nba.uth.tmc.edu/neuroscience/m/s2/chapter04.html Open source
  3. Betts, J. G., Young, K. A., Wise, J. A., Johnson, E., Poe, B., Kruse, D. H., Korol, O., Johnson, J. E., Womble, M., & DeSaix, P. (2022). Anatomy and physiology 2e. OpenStax. https://openstax.org/books/anatomy-and-physiology-2e/pages/1-introduction Open source
  4. Paré, M., Behets, C., & Cornu, O. (2003). Paucity of presumptive Ruffini corpuscles in the index finger pad of humans. The Journal of Comparative Neurology, 456(3), 260–266. https://doi.org/10.1002/cne.10519 Open source
  5. Chesler, A. T., Szczot, M., Bharucha-Goebel, D., Čeko, M., Donkervoort, S., Laubacher, C., Hayes, L. H., Alter, K., Zampieri, C., Stanley, C., Innes, A. M., Mah, J. K., Grosmann, C. M., Bradley, N., Nguyen, D., Foley, A. R., Le Pichon, C. E., & Bönnemann, C. G. (2016). The role of PIEZO2 in human mechanosensation. The New England Journal of Medicine, 375(14), 1355–1364. https://doi.org/10.1056/NEJMoa1602812 Open source
  6. McKemy, D. D., Neuhausser, W. M., & Julius, D. (2002). Identification of a cold receptor reveals a general role for TRP channels in thermosensation. Nature, 416(6876), 52–58. https://doi.org/10.1038/nature719 Open source
  7. Caterina, M. J., Schumacher, M. A., Tominaga, M., Rosen, T. A., Levine, J. D., & Julius, D. (1997). The capsaicin receptor: A heat-activated ion channel in the pain pathway. Nature, 389(6653), 816–824. https://doi.org/10.1038/39807 Open source
  8. Paricio-Montesinos, R., Schwaller, F., Udhayachandran, A., Rau, F., Walcher, J., Evangelista, R., Vriens, J., Voets, T., Poulet, J. F. A., & Lewin, G. R. (2020). The sensory coding of warm perception. Neuron, 106(5), 830–841.e3. https://doi.org/10.1016/j.neuron.2020.02.035 Open source
  9. Dubin, A. E., & Patapoutian, A. (2010). Nociceptors: The sensors of the pain pathway. Journal of Clinical Investigation, 120(11), 3760–3772. https://doi.org/10.1172/JCI42843 Open source
  10. International Association for the Study of Pain. (2020, July 16). IASP announces revised definition of pain. https://www.iasp-pain.org/publications/iasp-news/iasp-announces-revised-definition-of-pain/ Open source
  11. Melzack, R., & Wall, P. D. (1965). Pain mechanisms: A new theory. Science, 150(3699), 971–979. https://doi.org/10.1126/science.150.3699.971 Open source
  12. Mendell, L. M. (2014). Constructing and deconstructing the gate theory of pain. Pain, 155(2), 210–216. https://doi.org/10.1016/j.pain.2013.12.010 Open source
  13. Heinricher, M. M., Tavares, I., Leith, J. L., & Lumb, B. M. (2009). Descending control of nociception: Specificity, recruitment and plasticity. Brain Research Reviews, 60(1), 214–225. https://doi.org/10.1016/j.brainresrev.2008.12.009 Open source
  14. Che, T., & Roth, B. L. (2023). Molecular basis of opioid receptor signaling. Cell, 186(24), 5203–5219. https://doi.org/10.1016/j.cell.2023.10.029 Open source
  15. Makin, T. R., Scholz, J., Filippini, N., Henderson Slater, D., Tracey, I., & Johansen-Berg, H. (2013). Phantom pain is associated with preserved structure and function in the former hand area. Nature Communications, 4, Article 1570. https://doi.org/10.1038/ncomms2571 Open source
  16. Vaso, A., Adahan, H.-M., Gjika, A., Zahaj, S., Zhurda, T., Vyshka, G., & Devor, M. (2014). Peripheral nervous system origin of phantom limb pain. Pain, 155(7), 1384–1391. https://doi.org/10.1016/j.pain.2014.04.018 Open source
  17. Hanyu-Deutmeyer, A. A., Cascella, M., & Varacallo, M. A. (2023, August 4). Phantom limb pain. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK448188/ Open source

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