. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 798 Comparative Animal Physiology the ganglion. This graded synaptic potential is normally masked by the propagated response. In the superior cervical ganglion of the cat this synap- tic potential begins after a latency of 5 msec, reaches its peak at 10-20 msec, and falls to about 1/3 in 60-90 msec, many units rsponding out of phase (Fig. 299).^-'* The synaptic potential is absent when antidromic im- pulses enter the ganglion and is graded in size with the number of pre-gan- glionic impulses; it can summate on r
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 798 Comparative Animal Physiology the ganglion. This graded synaptic potential is normally masked by the propagated response. In the superior cervical ganglion of the cat this synap- tic potential begins after a latency of 5 msec, reaches its peak at 10-20 msec, and falls to about 1/3 in 60-90 msec, many units rsponding out of phase (Fig. 299).^-'* The synaptic potential is absent when antidromic im- pulses enter the ganglion and is graded in size with the number of pre-gan- glionic impulses; it can summate on repeated subthreshold stimulation. When transmission to interneurones and motoneurones in the spinal cord is blocked by nembutal a sensory volley sets up a synaptic potential which can be picked up either by focal microelectrodes in the cord or conducted electrotonically over ventral roots. In monosynaptic reflexes of cats the syn- aptic potential recorded focally in the spinal cord shows a delay of to msec, and peak time of to msec. Similar graded potentials have been recorded from the stellate ganglion of Loligo (Fig. 300)."^^^ ^^ The. Fig. 300. Synaptic potentials and emergent action potential spikes from stellate gang- lion of the squid. Lower record—spike in preganglionic fiber. Upper record—postgangli- onic spike developing later and later out of synaptic potential as fatigue occurs finally leaving only synaptic potential. From ;*' ^'^ propagated postganglionic spike arises out of the synaptic potential, and when motoneurones are fatigued only the synaptic potential remains. Di- rect stimulation of the ganglion can elicit a synaptic potential, but antidromic impulses cannot do so. It is postulated*'^ that the transmitter passes its peak before the beginning of the synaptic potential, and that the synaptic poten- tial must be of a critical size before the post-synaptic spike is evoked. SOMA RESPONSES. The soma of a central neurone refe
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