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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



FIG. 14. Diagram showing the method of excitation of the 

 inner coxal hair plate by a fold of the intersegmental membrane 

 of the second leg of the cockroach Periplaneta. ex, coxa, hp, 

 hairplate; pi, pleuron. [From Pringle (95).] 



with a short series of impulses and rapidly adapt; 

 these are in Limiilus the big cells located in the depth, 

 and in arachnoids organs which are not exactly iden- 

 tified anatomically but are located close to the slit 

 organs. The stretch receptors of some crustaceans are 

 composed of two sense organs lying close to each 

 other; one reacts tonically and the other one phasi- 

 cally. Each of these sense organs consists of a single 

 neuron which is located on a bundle of muscle fibers 



in Homarus and Cambarus. In other crabs, such as 

 Carcinus, many cells are combined in this organ. Some 

 of these cells react tonically, others phasically. The 

 tonic neurons show a resting discharge. The maximum 

 of this resting discharge of single neurons in Limulus 

 is present either at maximal extension or at maximal 

 flection of the joint. The minimum of the resting dis- 

 charge of the whole organ corresponds therefore ap- 

 proximately to a mean position of the membrane of 

 the joint 



The stretch receptor organs between the abdominal 

 segments of certain crustaceans, including Homarus 

 and Astacus, have been studied carefully. They are of 

 interest also from the standpoint of general physiology 

 since the activity of single sensory neurons could be 

 analyzed in them. The organs consist of two fine 

 bundles of muscles, RMi and RM2; a sensory neuron, 

 .SNi and SN^, is attached to each of these. This neuron 

 sends many dendrites to the muscle fibers. An afferent 

 axon is emitted from each neuron (fig. 15). The effer- 

 ent innervation consists of: a) motor fibers, innervat- 



FIG. 15. Schematic drawing of the stretch receptors between the segments of the tail of the crab 

 Astaau flmnatilis. RMi, muscle bundle of the tonic receptors; RM.>, muscle bundle of the phasic 

 receptors. SNj and SN^, sensory neurons of the tonic and phasic receptors respectively, Si and So 

 their afferent axons; MO], three thin motor fibers of the tonic receptors; MO;, thick motor nerve 

 fiber of the phasic receptors; and I, an inhibitory axon. (By courtesy of D. Burkhardt.) 



