Threshold Receptor Potential for Appearance of Impulses Ml/ 



Fig. 20. The threshold receptor potential of the mechanosensory neuron of 

 a chemosensory hair on the wing of Sarcophaga which is accompanied 

 by an impulse is plotted for a series of mechanical stimuli. In the 

 largest number of trials the threshold was 0-38 MV with the spread as 

 shown. (Redrawn from Wolbarsht, 1960.) 



of the receptor site and do not invade it ; changes in impulse size are due 

 to changes in the membrane resistance of the receptor site ; there is a 

 high resistance between the fluid-filled centre of the hair and the 

 general body fluid ; the value of this resistance is effectively determined 

 by the close anatomical conjunction of the receptor membrane and 

 the lumen of the hair cavity. In most respects the electrical response of 

 the insect mechanoreceptor is similar to that of the Pacinian corpuscle 

 of vertebrates. 



-r* 



_U^ 



f{rm'^''f^^rfmrf0m^^, 



t 



^tf^. 



O^^'^^f^v* 



10 

 MV 



Fig. 21. Response of mechanosensory hair on the anal plate of a female 

 Pliormia to changing mechanical stimulation. The left-hand arrow 

 indicates the approximate beginning of the deformation; the middle 

 arrow, the minimum; and the right-hand arrow, the return to the 

 undeformed position. Positive at the recording electrode is down. 

 Time marks recur at 0-2-second intervals. (Courtesy of M. L. 

 Wolbarsht.) 



