Skin is the human body's largest sensory organ. Understanding how it works will help roboticists create more useful android skins. We're a step closer to understanding the skin's sensory system thanks to a new report announced by Johns Hopkins researchers. The scientists created detailed maps of the branching patterns of sensory nerves in mouse skin. The resulting maps revealed ten distinct groups that seem to correspond to differences in nerve functions. For example, some nerve types gather information from a single hair follicle while others branch into groups that collect averaged information from 200 or more different locations. From the new release:
Nathans says the images now in hand will help scientists “make more sense” out of known responses to stimulation of the skin. For example, if a single nerve cell is responsible for monitoring a patch of skin a quarter of an inch square, multiple simultaneous points of pressure within that patch will only be perceived by the brain as a single signal. “That is why we can’t read Braille using the skin on our backs: the multiple bumps that make up a Braille symbol are within such a small area that the axon branches can’t distinguish them. By contrast, each sensory axon on the fingertip occupies a much smaller territory and this permits our fingertips to accurately distinguish small objects.
For all the details on the research, including lots of diagrams and images of the nerve networks, see the paper, "Morphological diversity of cutaneous sensory afferents revealed by genetically directed sparse labeling" (PDF format). In a related new release, Johns Hopkins researchers announced the discovery of strong evidence that there are specific nerve cells responsible for itch signals, distinct from nerves involved in pain.