. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 796 Comparative Animal Physiology Many invertebrate ganglia are likewise initially stimulated by high potas- sium or low calcium (see Table 69, Ch. 15, for heart ganglia). In crayfish abdominal ganglia in situ the effect of high potassium is to depress spon- taneous activity, whereas low potassium increases it. After a half hour of bathing in saline the reverse effects of potassium are observed.^^^^- ^^^' ^^ Ad- dition of acetylcholine to the bathing solution prevents the reversal in potas- sium action and sugge
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 796 Comparative Animal Physiology Many invertebrate ganglia are likewise initially stimulated by high potas- sium or low calcium (see Table 69, Ch. 15, for heart ganglia). In crayfish abdominal ganglia in situ the effect of high potassium is to depress spon- taneous activity, whereas low potassium increases it. After a half hour of bathing in saline the reverse effects of potassium are observed.^^^^- ^^^' ^^ Ad- dition of acetylcholine to the bathing solution prevents the reversal in potas- sium action and suggests that differences in behavior of intact and isolated ganglia may result from loss of ACh on isolation.'^^^ Transmission across synapses of the cockroach is remarkably unaffected by changes in potassium and calcium.^^^. tgc-:-_-_--^ (b) Fig. 298. Current flow at a synaptic junction; presynaptic fiber represented by vertical block and postsynaptic neurone by horizontal line. Current flow with presynaptic impulse {a) approaching synapse and (h) at synapse. Focal anode (Ai) followed by focal cathode (Ca). Cross hatching, region of the presynaptic impulse. Current flow repre- sented as toward region of negativity. From ;" ELECTRIC CURRENT. The action potential wave of the discharging axons may itself be an adequate stimulus for the receiving neurones. An electric shock of time relations similar to the action potential is an adequate nerve stimulus. In the oculomotor nucleus of the rabbit a volley of impulses in ascending axons, subthreshold for the motoneurones, can sum with a sub- hminal electric shock applied directly to the motor cells during the rising phase of the action ^- When two nerves are placed in proper con- tact side by side, an impulse can be transmitted from fibers of one ner\'e to the other. Transmission in such an artificial synapse, or ephapse, occurs if the impulse in the pre-ephaptic fiber stops at the junction so that the final pha
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