Biomedical Engineering Reference
In-Depth Information
FIGURE 7-21
Anatomy of the skin
and tactile
receptors. [Adapted
from (Brodel 1969).]
peak sensitivity occurs at stimulation frequencies of 200 to 300 Hz. Ruffini endings have
an unknown function and have never been found in the skin of the fingertips (Pasquero,
2006).
Temperature is sensed by two types of free nerve endings, with one type measuring
heat and the other type measuring cold. For temperatures above 45
◦
C and below 10
◦
C,
temperature also stimulates pain endings.
Tests with fine wires and small vibrators have been used to quantify the sensitivity
of different areas of skin. The static force required (Weinstein, 1968) varies from 0.05 g
on the lips to 0.63 g on the fingertips and belly up to 3.5 g on the sole of the foot. The
fingertip threshold corresponds to a skin indentation of about 10
m.
In regard to vibration, Geldard (1957) useda1cm
2
vibrator and found that the
fingertips were the most sensitive of all the body locations by at least an order of magnitude.
The abdomen was found to be 60 times less sensitive than the fingertips for 200 Hz
vibrations.
μ
