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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



pyramidal cells may become active without activity 

 of their apical dendrites resulting. They suggest the 

 possibility that in normal cortical iiehavior dendritic 

 activation is minor. Activation of dendrites via paths 

 in addition to the afferent radiation must also be con- 

 sidered, although in the present case the radiation 

 impulses form the major component. 



Neurons e.xert their influences on their surrounds 

 by way of their axon discharges, but neurons may re- 



no. 4. Possible pattfins oi activation of neurons in the corte.x. 

 The afferent radiation axon entering; at right activates the 

 Golgi cell 6'i, the axon .-1 of which in turn activates the pyram- 

 idal cell Pi at its cell body and induces a brief spike response. 

 .\ recurrent branch of the axon of Pi is shown activating G^, 

 which in turn activates P,; etc., accounting for the alternate high 

 and low spike sequences of the response. Circuits from other 

 sources are able to activate the dendrites of Pi and set up slow 

 wave responses. B is such a circuit ending along the apical 

 dendrite, C ending at its terminals and D ending on the basal 

 dendrites. [From Clare & Bishop (37).] 



ceive their effects either through cell body synap.ses or 

 through their dendritic synapses. Activation through 

 cell body synapses has been considered to require 

 more than a single impulse. The required number 

 may reach the cell body via several branches of one 

 axon synap.sing with the given cell body, or via several 

 axons, or several impulses via one axon. The above 

 mentioned authors deduce that when a cell body is 

 intensely activated, its continued firing for a time 

 after input has ceased depends upon the beha\ior of 

 dendrites. These dendrites were activated bv the cell 



body and now in turn are reactivating the cell body 

 or, as we might say, keeping it active. The dendritic 

 contribution acts like a steady current stimulus to the 

 cell body. 



What has already been said in describing the initial 

 spikes in the nerve has been interpreted as picturing a 

 sequence of activations from lower levels in the cortex 

 to the surface. A slow surface positive wave associated 

 with the spikes is another component of the response. 

 A negative wave immediately follows the positive one, 

 and it is found in the lower third of the cortex, proba- 

 bly originating in layer IV. Prior to this negative 

 wave, there is another negative wave. It occasionally 

 shows up in a normal record and becomes the most 

 conspicuous part of a record under strychninization in 

 which case it occupies the whole depth of the cortex. 

 Not only do the two negative waves seem to have dif- 

 ferent origins, but the late negative wave is belicxed 

 to arise from cells other than those responsible for the 

 positive components in the record. The first negative 

 wave is attributed to conduction from cell bodies via 

 apical dendrites toward the surface of the cortex. 

 When not present in the normal record, its absence is 

 a sign that such conduction is not induced by cortical 

 stimulation. In weakly strychninized preparations, 

 before any detectal:)lc effect is produced upon the 

 surface positive components, the response represented 

 by the negativity in question is made evident. When 

 large positive responses are induced, they are followed 

 immediately by the early negativity. Lower responses 

 are characterized by a delay between the positive and 

 negative waves. In these records, the two negative 

 waves are distinguishable. 



Bishop & Clare (20) interpret the early positive 

 wave as representing the activity of the basal dendrites 

 of the neurons of which the spikes indicate the activity 

 of cell bodies. In figure 5 is presented the diagram 

 given by Bishop & Clare to indicate the nature and 

 origin of the five components of the cortical response 

 of the cat. Figure 6 shows the findings of Bishop & 

 O'Leary (25) on the rabbit. In both the cat and the 

 rabbit, the final component of the response may 

 repeat several times at the rate of the alpha rhythm. 



Chang & Kaada (33) also analyzed the cortical 

 response to optic nerve stimulation. The description 

 is much like the one we have just given. Some of their 

 interpretation was different from that of Bishop's 

 laboratory. The authors did point out, however, that 

 it is only the slow waves of the various components 

 of the response that are reduced by agents affecting 

 the cortex. This is in line with findings of Bishop's 

 laboratory over the years. 



