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HANDBOOK OF PHVSIOLOGV 



NEUROPHYSIOLOGY I 



Stem the position of the pain pathways correlates 

 poorly with the position of Marchi degeneration in 

 spinotectal and spinothalamic fibers. 



Impulses from somatic nerves were traced into 

 the anterolateral column of the cat's spinal cord by 

 Collins & Randt (49). They studied with 10 m tip 

 microelectrodes the responses evoked from stimula- 

 tion of contralateral sciatic or superficial radial 

 nerves, and compared these with the responses to be 

 seen in the ipsilateral dorsal column. Velocities of 

 impulses were compared for the two loci both in the 

 peripheral nerve and in the cord. The responses in 

 the anterolateral quadrant were related to the 

 gamma component in the nerve. In the peripheral 

 nerve they traveled at about 34 m per sec; in the 

 cord they averaged 24.9 m per sec. ranging from 19 

 to 33 m per sec. The dorsal column impulses while 

 in the peripheral nerve traveled at about 85 m per 

 sec. and slowed down to an average of 50.5 m per 

 sec. in the cord. The typical anterolateral potential 

 had slow rising and falling phases with superimposed 

 spike activity which was maximal at the peak of 

 the slower potential. The maximum voltages were 

 from 50 to 75 Mv, the total duration was 30 to 40 

 msec. The ratios of threshold potentials in the 

 anterolateral column to the dorsal column were 

 2.6:1 for a 5 msec, shock, corresponding closely to 

 the ratios of these potentials in peripheral nerve of 

 2.4:1. The anterolateral column potentials traverse 

 this portion of the cord throughout its length as 

 shown by their abolition in a cervical lead following 

 thoracic anterolateral section (which leaves intact 

 the cervical dorsal column potential). 



Impulses from autonomic nerves were traced into 

 the anterolateral column of the cord of rabbits, cats 

 and dogs by Amassian (5). He recorded with micro- 

 electrodes the responses excited by stimulation of the 

 splanchnic nerve. When this was increased to 15 v. 

 with a o. I msec, shock a large fraction of 'A' gamma- 

 delta fibers in the nerve was excited. A barrage of 

 spikes could then be seen bilaterally in the antero- 

 lateral region of the cord clo.se to the gray matter. 

 Its long latency of 1 1 to 13 msec, and much greater 

 duration of 25 msec, distinguished it from the pos- 

 terior column wave. There is a striking similarity 

 between these potentials and those recorded after 

 stimulation of somatic nerves from almost the same 

 spots in the cord, the splanchnic responses a bit 

 medial to those from the somatic nerves. The high 

 voltage required provoked reflex movements of the 

 body wall, but such motor actixity did not then set 

 up the whole potential in the anterolateral column 



because this was only partially reduced when the 

 movements were stopped with </-tubocurarine. 

 Amassian is appropriately cautious about correlat- 

 ing this pathway with that subserving visceral pain 

 in man. Both clinical and experimentally induced 

 pain in gastrointestinal and urinary viscera is usually 

 stopped in patients by anterolateral cordotomy on 

 the side opposite a laterally placed viscus. So the 

 crossover of splanchnic pain fibers appears to be 

 more complete in man than the fibers from which 

 Ama.ssian was recording. Visceral aff"erent path- 

 ways in the cat had already been shown to be in- 

 completely crossed by Spiegel & Bernis (253) who 

 found that stimulation of the central end of one 

 splanchnic nerve caused 'pain responses' until both 

 anterolateral columns were destroyed. 



The following evidence indicates that impulses for 

 pain may not ascend the cord exclusively via a single 

 fiber running in the anterior or anterolateral white 

 matter to reach the brain stem, a) Vigorous stimula- 

 tion, as with bipolar electrodes at 100 or more v., 

 consistently causes pain in an area apparently de- 

 nervated by full anterior quadrant section as judged 

 by analgesia to pinprick and to a variety of other 

 forms of experimentally induced pain (296, p. 45). 

 King's (141) careful measurements revealed that 

 threshold voltage values for pricking pain on the 

 analgesic side were only 40 to 50 per cent greater 

 than on the normal side. That the pain impulses are 

 not entering the cord at levels above the cordotomy 

 incision, having moved rostrally along sympathetic 

 pathways in the paravertebral trunks or along the 

 aorta, is reasonably certain because the finding is 

 the same following high cervical cordotomy. 6) 

 Direct bipolar electrical stimulation applied to the 

 surface of the posterior and posterolateral columns 

 of the cord in man causes severe tingling sensations 

 like an electric shock. Foerster & Gagel (80) de- 

 scribed such responses; we confirm that at low 

 thresholds (of less than o.oi v. in our hands) applica- 

 tion of the electrodes to the fasciculus cuneatus 

 causes reference to the ipsilateral leg or pelvis, and 

 to the fasciculus gracilis causes reference to the 

 ipsilateral arm. At higher thresholds one evokes 

 similar responses contralaterally from the surface of 

 the posterolateral column of white matter. That 

 such pathways are rarely used in pain of clinical 

 cause is clear from the high percentage of patients 

 relieved of pain by anterior quadrant section. Pos- 

 sibly these observations have in fact no physiologic 

 significance, and electrical stimulus to the exposed 

 spinal cord may be a condition for which there is no 



