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J Useful Biophysical Data
Table J.12 I feel your pain
Nociceptor locations:
Skin Types:
Mech., Therm., Chem., Polymodal
Joint Types:
Mech., Polymodal, Silent a
Visceral Types:
Pressure, Temp., Chem., Silent
Density of Aδ type b in skin
<2/mm 2
Density of C type in skin
4 − 8/mm 2
Depth of skin nociceptors
20 − 500 μm
Separation, visceral nociceptors
0.2–2 cm
Speed of signal in Aδ type
2–20 m/s
Speed of signal in C type
<2 m/s
Thermal activation of Aδ
>46 ◦ C
Thermal activation of C
> 41 ◦ C
a Silent nociceptors are activated after a time of stimulation above a certain threshold.
b Aδ type cause quick sharp pain; C type are slower; acting after lingering damage.
Table J.13 The human touch
Meissner corpuscle
Fine touch
Merkel cell
Touch pressure
Ruffini corpuscle
Skin shear
Pacinian corpuscle
Skin vibration
Root hair plexus
Proximal movements
Free nerve endings
(See pain table)
Weight of skin (adult human)
4.1 kg
Surface area of skin (adult human)
∼1.8 m 2
Number of tactile receptors in the hand
17,000
Number of nerve endings in hand
200/cm 2
von Frey sensitivity threshold (Face)
4.9 dynes
Two point separation threshold (Finger)
2–3 mm
Length of dermis Meissner’s nerve corpuscle
90–120 micron
Density of receptors on finger tips
2500/cm 2
Density of Meissner’s corpuscles on finger tips
1500/cm 2
Density of Merkel’s cells on finger tips
750/cm 2
Density of Pacinian corpuscles on finger tips
75/cm 2
Density of Ruffini’s corpuscles on finger tips
75/cm 2
Thermal pain threshold
45 ◦ C