MECHANICS AND NEURAL RESPONSE OF RECEPTOR SYSTEMS 



403 



to the actual motion, but probably gives 

 correct orders of magnitude for such de- 

 rived quantities as average linear accelera- 

 tions, etc. 



3. The maximum linear accelerations en- 

 countered aboard naval vessels are about .8 

 g; the average (over various points and 

 various classes) accelerations are probably 

 .3 g or less. Maximum angular accelera- 

 tions can be as high as 49° per sec.^ 



4. Continuous records of roll and pitch 

 can be obtained using gyroscopic equipment 

 of the fire-control type. 



5. For any one vessel there are unique 

 spectra of roll and pitch characteristics, 

 and it is essential that these spectra be de- 

 termined from the continuous records. 



6. The action of waves modifies to some 

 extent (e.g., Doppler effect) the periods and 

 amplitudes of the motion, but the charac- 

 teristics of the ship seem to play the domi- 

 nant role in governing the motion. 



Mechanics and Neural Response 



OF THE Receptor Systems 

 Prior to a discussion of the response of the 

 labyrinthine receptors it is useful to have in 

 mind a simple model of their mechanical 

 arrangement (Fig. 2). One may imagine 

 each sacculus and utriculus to consist of a 

 saucer-shaped base lined with sensory epi- 

 thehum (macula). Overlying the epithe- 

 lium is attached a membrane of greater 

 specific gravity (otolith) (40). It appears 

 (1) that, in these receptors, effective stimu- 

 lations are those which tend to pull the 

 otolith away from the macula; one may 

 imagine that in such cases the hairs of the 

 sensory epithelium are stretched. There 

 is some evidence (20), however, indicating 

 that these organs also respond continuously 

 under static conditions. The second class 

 of receptor organs is that of the semicircular 

 canals (Fig. 2). Any one canal may be re- 

 garded as a doughnut-shaped rigid con- 

 tainer filled with fluid (endolymph).* Ex- 



^ That the fluid outside of the central canal 

 plays any role seems to be ruled out by the experi- 

 ments of Dohlman (12) . 



tending into the canal, at the enlarged 

 region (ampulla), there is a projection (the 

 cupula) hinged at its base (crista), in which 

 base lies the sensory epithelium. Any 

 accelerations — either acting directly on the 

 cupula or transmitted by the endolymph — 

 which cause a deflection of the cupula are 

 adequate stimulation (39) ; presumably these 

 deflections stretch the hairs of the sensory 

 epithelium imbedded at the cupular hinge. 

 It has already been stated that in the 

 sacculus and utriculus as well as in the 



Fig. 2. Schema of the utriculus (u) and sacculus 

 (s) of the right side, and the canals of the left side. 



canals, stimulation results from the deflec- 

 tion of an elastic (and also viscous) structure. 

 One must, however, know the nature of the 

 relation between the extent of deflection and 

 the neural response of the receptors. In 

 the case of the canals, this relation has been 

 elucidated by a number of classical studies. 

 Steinhausen (39, 11) first clearly demon- 

 strated on the pike that cupular deflection 

 was quantitatively associated with signals 

 emitted from the receptors — using as a 

 criterion of activity the nystagmic response. 



