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HANDBOOK OF PH\SIOLOGY 



NEUROPHYSIOLOGY II 



as well as the deterioration of such protective func- 

 tions as temperature and blood glucose homeostasis. 

 The routes of these connections are then of interest, 

 although our information is at best sketchy. It has 

 been suggested by Gillilan (62) that the so-called 

 reticulospinal tracts of Papez (129) are concerned 

 with autonomic activity. These include a) the lateral 

 reticulospinal tract, located in the medial part of 

 the lateral funiculus and said to be concerned with 

 thermoregulatory sweating on the face; h) the ventral 

 reticulospinal tract wiiich lies in the \ entral funiculus 

 and is concerned with va.scular control and sweating 

 of the body and extremities; r) the ventrolateral 

 reticulospinal tract in the ventrolateral part of the 

 lateral funiculus which participates in regulation of 

 respiration, being connected with the motor neurons 

 of the respiratory muscles and having origin, it is 

 said, in the respiratory areas of the brain stem; d) 

 the medial reticulospinal tract in the anterior funicu- 

 lus which is said to descend from various autonomic 

 areas of the brain stem and ma>' help integrate para- 

 sympathetic and sympathetic activities. The location 

 of descending sympathetic fibers in the anterolateral 

 white matter of the spinal cord was noted by Sherring- 

 ton (153) in 1887; this localization has been reaffirmed 

 clinically many times more recently by chordotomy 

 for relief of pain. Experimentally in animals there 

 is good evidence for such a location for descending 

 fibers mediating pressor and bladder responses (171). 

 The pressor pathways undergo partial decussation in 

 the brain stem and are multisynaptic above the spinal 

 cord, at least. There are also decussations below the 

 cervical cord level, both for pathways from the 

 hypothalamus and from the medulla oblongata; some 

 backcrossing is also present in the spinal cord accord- 

 ing to Harrison ft al. (71). Thus, stimulation of 

 sympathetic areas on the right side of the brain stem 

 may produce effects on the same side even after hemi- 

 section of the cord in the cervical region. Descending 

 pathways for bladder contraction have decussations 

 in the brain stem and lower lumbar segments in ani- 

 mals but have no cross connections in the remainder 

 of the cord. Pathways for respiratory control lie in 

 the anterior and anterolateral portions of the white 

 matter in cats (135). Pressor respon.ses of cerebral 

 c jrtxal origin are also mediated by bilateral pathways 

 in the anterolateral region (95). In general, these 

 localizations seem also to apply in man, since Foerster 

 (52, 53) found evidence in his patients of bilateral 

 pathways for vasoconstriction and sweating in this 

 anterolateral region. 



When these rich paths for the modulation of auto- 



nomic activity in the spinal cord are severed, certain 

 ijasic patterns are retained and remain functional at 

 a reflex, automatic le\el. We have noted that va.so- 

 motor and \'iscerosomatic reflexes may remain active. 

 It is well-known that the mechanisms for defecation 

 and micturition may regain adequate levels of reflex 

 function and may be subject to a degree of control by 

 imposed cutaneous stimulation. The neural patterns 

 for sexual function remain and can operate wiihc^ut 

 the influence of the brain, provided the proper hor- 

 monal milieu is present. In animals, these patterns 

 include appropriate somatic attitudes. Temperature 

 adjustments remain poor. In this homeostatic function 

 the diencephalon is pre-eminent. 



Spina/ Shock 



The phenomena of acute spinal shock are es- 

 pecially striking in so-called higher echelons of the 

 vertebrate group. In lower forms reflex activity may 

 proceed without delay after severance of the spinal 

 cord, but in primates there is a lull in the functioning 

 of the isolated cord which in the past has posed prob- 

 lems to the clinician. In general, autonomic functions 

 are less affected than somatic, although the onset of 

 automaticity of bladder and bowel functions may be 

 considerai)l\' delayed, even in carnivores. The cause 

 of spinal shock cannot be stated precisely, although 

 Sherrington hypothesized a possible 'isolation dys- 

 trophy' afTecting neurons of the spinal cord after 

 separation from higher mechanisms. Certainly the 

 cord neurons, normally adapted to powerful extrane- 

 ous influences, excitatory and inhibitory, which are 

 probably chemical, must undergo a dramatic change 

 in reactivit)- when these influences are cut off. In 

 lower forms these influences seem chiefly reticulo- 

 spinal and vestii)ulospinal (57); in man, however, the 

 corticospinal connections seem more important. Since 

 visceral mechanisms are perhaps ordinarily less mod- 

 ulated by impulses from the brain than are the 

 somatic, these readapt with greater facility than the 

 latter. Howe\'er, some of the great liomeostalic 

 complexes, temperature regulation for instance, can- 

 not rea.ssume function when the brain connections 

 are severed. 



Influence of Distance Receptors 



Sherrington considered the great influences of the 

 brain upon both autonomic and \oluntary activities 

 to be dependent upon the dexelopment of the dis- 

 tance receptors — "the great inaugurators of reaction.' 



