CENTRAL AUTONOMIC MECHANISMS 



953 



tions of these outflows, the location of the cell bodies 

 of the neurons giving rise to the preganglionic fibers, 

 and of so-called internuncial neurons which may 

 participate in visceral reflex circuits. Gaskell in 1885 

 noted that the distribution of neurons in the 'lateral 

 horn' (intermediolateral gray column) corresponded 

 closely with the distribution of the thoracicolumbar 

 sympathetic fibers, and he suggested that the cells of 

 this group gave rise to these fibers. It is interesting 

 incidentally that Gaskell did not approve the terms 

 preganglionic and postganglionic. It was his view 

 that the neurons we are accustomed to call post- 

 ganglionic (after Langley) were simply shifted from 

 their original position during development, retaining 

 their functions and relationships as "effector' or 'motor' 

 elements, in other phraseology, forming the lower 

 motor neurons of the sympathetic system. The neurons 

 of the intermediolateral gray column, then, according 

 to Gaskell, are "connector" neurons presumably 

 homologous with similar neurons which may ije inter- 

 calated between pyramidal tract fibers and the 

 anterior horn somatic motor neurons. There are 

 certain merits in this proposal. 



The preganglionic spinal neurons are smaller than 

 the somatic efferent cells and are also multipolar, with 

 finer and more .scattered chromidia which are es- 

 pecially concentrated at the periphery of the peri- 

 karyon. The chromidial pattern is quite variable and 

 makes the determination of chroma toly tic or otlier 

 pathological changes difficult and often undependa- 

 ble. According to Mitchell (121) cells of this type 

 ha\e been found elsewhere in the cord than in the 

 intermediolateral column, and an intermediomedial 

 column has been described. However, in man tliere is 

 said to be no definite column in the medial part ot 

 the pars intermedia but simply scattered cells of this 

 type. Although some of these cells may simply be 

 intercalated neurons devoted to other functions, it 

 would not ije surprising if there were some variable 

 scatter from the lateral column. Mitchell also makes 

 a point of mentioning that autonomic type neurons 

 ha\e l)een descrilied in the dorsolateral portions of the 

 anterior gray columns in the cer\ical region and 

 stresses the pro.ximity of these neurons to the spinal 

 accessory roots. Small myelinated fibers from the 

 latter have been traced into the \agus nerve; and 

 while these may perhaps be sympathetic, the possi- 

 bility that the neurons mentioned may i^e displaced 

 cranial parasympathetic elements has not been con- 

 sidered. It is also po.ssible that they are related to the 

 nucleus amijiguus and concerned with control of cer- 

 tain striated muscles of the neck. 



Spinal Aiitonnmic Reflexes 



It is generaliv held that spinal autonomic reflex arcs 

 may be monosynaptic or multisynaptic (26, 27). The 

 latter t\ pes make provision for delayed responses and 

 enduring reactions in which there is considerable after- 

 discharge. They also must provide for inediation of 

 certain types of suprasegmental control, including 

 facilitation and inhii^ition, much as in somatic re- 

 flexes as indicated by Eccles (49). The anatomical 

 identity and specific connections of these internuncial 

 neuron pools are not well-known, although there must 

 be provision for such mechanisms as reverberating 

 circuits. 



The organization of these reflex neuronal pools is 

 primarily segmental, not necessarily in the sense of 

 single segments but involving certain groups of seg- 

 ments, as is shown in the following list for thoraci- 

 columbar reflexes [modified from Kuntz (99)]. 

 Head and neck T1-5 



Upper extremits' T2-9 



Lacrimal gland (sympathetic) T1-3 



Vasomotor responses, piloerection and 

 sweating 

 upper trunk T4-9 



lower trunk T9-L2 



lower extremities T12-L2 



Pupillodilatation C8-T1 (2) 



Cardiac acceleration T2-6 



Abdominal viscera T4-L2 



Genitourinary and rectoanal (sympa- L1-L2 

 thetic) responses 

 It is obvious that these may vary considerably. There 

 may also be interactions among these reflexes as well 

 as mass discharges involving many of them. It is 

 commonly held that mass discharge is a characteristic 

 of the thoracicolumbar system, while more specific 

 effects are produced by the craniosacral division. 

 This usually loosely stated view is related to the rela- 

 tively long-lasting effects of the chemical effector 

 substances produced by the orthosympathetic ele- 

 ments. However, while it is in general true, one must 

 make some reservations even as did Cannon (37) 

 who, although he stressed the diffuse discharge idea, 

 said, ""The sympathetico-adrenal system though or- 

 ganized for diffuse and widespread action may influ- 

 ence excessively separate organs or functions." More 

 specifically, recent experiments have shown that 

 autonomic discharges may be largely segmental (61). 

 Thus, stimulation of the spinal cord in animals at T4 

 produces a marked rise in arterial pressure without 

 pupillary dilatation. On stimulation from T3 to Ti, 

 the pupil response appears and increases while the 



