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Tactile innervation densities across the whole body
Giulia Corniani1,2, Hannes P Saal1,2,3
1Active Touch Laboratory, Department of Psychology, University of Sheffield, Sheffield, United Kingdom.
Journal of Neurophysiology
|September 23, 2020
Summary
The human skin has approximately 230,000 tactile afferent nerve fibers. Their density varies by body region, impacting touch sensitivity and decreasing with age.
Area of Science:
- Neuroscience
- Dermatology
- Sensory Physiology
Background:
- The skin, our largest sensory organ, receives tactile information via afferent nerve fibers.
- Innervation density varies significantly across body regions, with incomplete estimates for total tactile fibers.
- Existing data on tactile afferent fiber numbers and distribution are inconsistent.
Purpose of the Study:
- To reconcile existing estimates and provide comprehensive ranges for tactile fiber types innervating skin.
- To determine the total number of tactile afferent fibers in the human body.
- To investigate the relationship between innervation density, spatial acuity, and cortical representation.
Main Methods:
- Reconciliation of data from dorsal root counts, microneurography, histology, and psychophysics.
- Estimation of fiber numbers and density across different skin regions.
- Correlation analysis between innervation density and psychophysical measures.
Main Results:
- Estimated ~230,000 tactile afferent fibers in young adults, decreasing 5-8% per decade with aging.
- Palmar skin of hands (15%) and face/lips (19%) show high innervation density.
- Innervation density correlates with spatial acuity and, on hairy skin, hair follicle density.
Conclusions:
- Provides a robust estimate of tactile afferent innervation across the human body.
- Highlights the significant role of innervation density in tactile perception and spatial acuity.
- Suggests innervation density partially explains but does not fully account for cortical magnification of certain body areas.
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