Fingertips Increase Sensitivity to Touch

close up view of a human finger tip of a white person with a blue background

Biological Strategy

Humans

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Sense Touch and Mechanical Forces in a Living System

Perceiving touch enables living systems to detect other living systems around them and environmental conditions, such as air movement, water currents, and temperature. This ability can help them sense danger as well as opportunity, as when a Venus flytrap’s hairs sense the presence of an insect to eat. Sometimes, a living system senses touch or mechanical forces at a coarse scale; other times, at a sensitive scale that detects very subtle differences. For example, a human elbow is not nearly as sensitive to textures as human fingertips. Fingertips have dermal ridges and many nerve endings that increase sensitivity, enabling them to explore the environment in detailed ways. Elbows don’t need to sense at that level of detail.

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Sense Shape and Pattern in a Living System

Living systems must identify other living systems and objects to navigate, feed, escape predators, find resources, and more. The ability of living systems to “see” varies widely, with “seeing” including not only sight, but other means of sensing shapes or patterns, such as smell or echolocation. For example, a hawk can see much more detail than humans while other organisms can see far less detail. Nevertheless, each living system is capable of detecting shapes and patterns to the extent it needs to for survival. In addition to perceiving physical shapes or patterns, living systems can also sense landscape patterns at various scales. The purple sea urchin, for example, does not have eyes, yet can pick out fine details in its environment by using its entire surface as a compound eye. The urchin’s spines shield light coming from wide angles, further refining its focus.

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Mammals

Class Mammalia (“breast”): Bats, cats, whales, horses, humans

Mammals make up less than 1% of all animals on earth, but they include some of the most well-known species. We know first-hand some of the characteristics that make mammals unique, like having hair, being able to sweat, and producing milk through mammary glands. Another critical shared feature is a set of highly-specialized teeth. Unlike sharks or alligators, for example, whose teeth are generally all the same size and shape, mammals have differently shaped teeth in different areas of the jaws to target specific foods or foraging strategies.

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Fingertips increase touch sensitivity due to mechanoreceptors underneath the surface of the skin

Human fingertips are probably the most sensitive skin areas in the animal world; they can feel the difference between a smooth surface and one with a pattern embedded just 13 nm deep. This is due to epidermal ridges on the surface of the fingertip, which allow humans to differentiate between a wide range of textures, materials, temperatures, and pressures. While each person has a unique pattern of ridges (i.e. fingerprints), the pattern is not crucial to the function. Just underneath the ridges are mechanoreceptors, a type of sensory receptor that responds to tactile stimulus. Friction caused by movement of the fingertip along a surface or material stimulates the mechanoreceptors, which then transmit the tactile information to the brain.

There are four major types of mechanoreceptors on smooth (non-hairy) parts of mammalian skin: lamellar corpuscles, tactile corpuscles, Merkel nerve endings, and bulbous corpuscles. Lamellar corpuscles respond to changes in vibration and pressure, while tactile corpuscles are particularly sensitive to light touch. Merkel nerve endings respond to general changes in pressure and location, as well as deep static touch, such as edges and overall shape. Bulbous corpuscles are sensitive to skin stretching and slippage of an object against the skin, allowing for improved grip.

This strategy was contributed by Safi Marroun and Teresa McNulty.

Last Updated August 17, 2017

References

Journal article

Feeling small: exploring the tactile perception limits

Scientific reports. 3(2617): 1-6. | Skedung L, Arvidsson M, Chung JY, Stafford CM, Berglund B, Rutland MW.

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Reference

“Four major types of encapsulated mechanoreceptors are specialized to provide information to the central nervous system about touch, pressure, vibration, and cutaneous tension: Meissner’s corpuscles, Pacinian corpuscles, Merkel’s disks, and Ruffini’s corpuscles. These receptors are referred to collectively as low-threshold (or high-sensitivity) mechanoreceptors because even weak mechanical stimulation of the skin induces them to produce action potentials. All low-threshold mechanoreceptors are innervated by relatively large myelinated axons, ensuring the rapid central transmission of tactile information.” (Purves et al. 2001).

Book

Mechanoreceptors Specialized to Receive Tactile Information

Sunderland (MA): Sinauer Associates. Chapter 9, Neuroscience, 2nd edition | Purves D, Augustine GJ, Fitzpatrick D, et al.

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