Touch, Temperature and Pain
Skin receptors encode mechanical, thermal and potentially damaging stimuli. Receptor density, receptive fields and central connections help explain tactile acuity and the distorted cortical body map. Spinal and descending modulation help explain why felt pain does not directly measure tissue damage.
What a learner can do afterwards
- Relate receptor type and adaptation rate to the kind of touch each one reports
- Explain why the cortical body map is distorted and what sets the distortion
- Describe one mechanism that can inhibit or amplify onward nociceptive transmission in the spinal cord.
1 · Read
Skin mechanoreceptors encode pressure, vibration or stretch; thermoreceptors encode warmth or cold. Nociceptors detect potentially damaging mechanical, thermal or chemical stimuli. This nociception differs from felt pain. A capsule covers a nerve ending. Free endings lack capsules and include temperature and nociceptive endings. Encapsulated endings include touch receptors, but Merkel touch endings are unencapsulated.
Rapidly adapting receptors respond strongly to changes, then quieten under steady input. Slowly adapting receptors maintain responses while pressure continues. Rapid adaptation helps steady clothing become less noticeable, but does not silence every touch receptor. Attention also affects what you notice.
Body skin to cortex: 3-neuron model excludes local interneurons. Dorsal-column touch: primary soma in dorsal root ganglion; medullary crosses in medulla; thalamic to somatosensory cortex. Spinothalamic pain/temperature: neuron 2 crosses in cord. Spinal circuits inhibit/amplify nociceptive input. Painless touch may recruit inhibitory interneurons. Descending brain input alters spinal processing. Gentle rubbing by a minor bump may ease pain; relief varies. Pain is no direct tissue-damage measure.
Dorsal-column model: each cell names one neuron in the ascending chain. The third projects to cortex, the destination outside this count.
A receptive field is the skin region where stimulation affects a neuron's response. Fingertips have dense touch innervation and many small fields. At the same suitable spacing, contacts give more distinct population patterns than on the back, not one cortical column per contact. Like visual maps, the body map assigns unequal space. Peripheral sampling and central connections shape it: hands get much more cortex per skin area than the torso.
Tuning and adaptation shape receptor input. Peripheral sampling and central processing support spatial detail. Spinal and descending modulation mean pain does not directly measure damage.
Three readings written for this dataset. Video: "Somatosensory tracts", Khan Academy.
More to read
Skin signals and adapting receptors
Different skin endings turn mechanical forces, temperature changes and potentially harmful stimulation into neural signals. Rapidly adapting receptors respond strongly when input changes, then reduce their response if it stays constant. Slowly adapting receptors continue responding during sustained stimulation. This difference can make unmoving clothing less noticeable without eliminating all touch information. What you attend to also changes your awareness. Temperature-sensing endings and nociceptors can lack a capsule. Some touch receptors are covered by capsules; Merkel endings sense touch without one.
Why the body map has unequal proportions
Hands and lips receive disproportionately large shares of the cortical body map compared with the torso. Their shares are not proportional to skin area. Both peripheral sampling and connections within the central nervous system help determine the allocation. For a skin neuron, its receptive field is the area whose stimulation changes its response. Fingertips combine closely spaced touch innervation with small receptive fields, allowing nearby contacts to generate more distinguishable population activity. The back can distinguish spatial detail too, but less finely.
How spinal processing can alter pain
Detecting and encoding stimulation that could damage tissue is called nociception. Experiencing pain is a different process. Within the spinal cord, local circuits can reduce or strengthen signals passed onward. Touch that does not hurt may activate inhibitory interneurons, which suppress some nociceptive transmission. Signals travelling down from the brain also modify spinal processing, including influences from attention and context. Light rubbing beside a minor bump can sometimes ease discomfort, though the amount of relief varies. These changes help explain why the strength of pain is not a direct reading of tissue damage.
Explore more
2 · Watch
En anglaisTake it off screen
Where it sits
Optional connections
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.