138 



HANDBOOK OF I'HVSIOLOGV 



NEUROPHYSIOLOGY I 



more specialized sense organs. For example the 

 ability of the cochlea of the higher vertebrates to act 

 as a frequency analyzer is due to its mechanical prop- 

 erties (97). In compound eyes the distribution of 

 absorbing pigments affects the distribution of light on 

 the receptors so as to increase cither the sensitivity 

 or the discrimination of the eye (84). The same situa- 

 tion can be seen if the skin is taken as a whole. It has 

 been shown that thermal receptors respond to the 

 temperature at a given point at a given time (106); 

 the distribution, both in time and space, of tempera- 

 ture in the skin, and consccjuently the nature of 

 sensation aroused, will depend on the physical proper- 

 ties of the whole system. Another, and rather different, 

 example of the effect of external physical factors is 

 the decrease in the rate of adaptation of mechanical 

 receptors in frog's skin that occurs as a result of 

 stretching the skin (68). 



All the examples mentioned in the last paragraph 

 refer to the physical properties of a whole tissue or 

 organ and their effect on the behavior of a population 

 of receptors. The factors involved in the transmission 



of energy inside what is normally described as a 

 single ending can also be of fundamental importance. 

 The Pacinian corpuscle consists of a central core sur- 

 rounded by thin laminae which form the boundaries 

 of coaxial spheroids; the spaces between the laminae 

 are filled with fluid. When the ending is .squeezed 

 displacements of the laminae occur and these can be 

 recorded from photographs taken with short flashes 

 (51, 52). During and immediately after the onset of a 

 compression, relatively large displacements of the 

 laminae occur (fig. 10 lejt); but these decline rapidly 

 to a steady value which is maintained as long as the 

 corpuscle is compressed. This maintained displace- 

 ment \aries with the position of the lamina measured, 

 those near the periphery of the corpuscle showing large 

 displacements while those near the center show none; 

 figure 1 1 is a plot of maintained displacement against 

 distance from the center of the corpuscle. The time 

 course of the compression can be recorded and there- 

 fore the displacement that would be expected at any 

 instant, if the response of the system were inde- 

 pendent of time, can be calculated. Subtraction o 



2 4 



70 



so 



Fig. II 



.III 



flOO 



II 200 



2>L 



300 



500 



600 M 700 



FIG. 10. Mechanical properties of the Pacinian corpuscle. Left: time course of displacements 

 of 3 laminae (see inset) during a compression that started at / = o, rose linearly to / = 2.6 msec, 

 and then remained constant. Right: dynamic component' of displacement. See text. [By courtesy 

 of S.J. Hubbard.] 



FIG. II. Mechanical properties of the Pacinian corpuscle. Abscissa: diameter in the transverse 

 plane (2r). Ordinate: maintained displacement of laminae as functions of transverse diameters 

 (■2Ar). t marks edge of the central core. Bars indicate ±2 X standard error. [By courtesy of S 

 J. Hubbard.] 



