CHAPTER L 1 1 



The reticular formation 



J. D. FRENCH 



Veterans Administratiun Hospital, Long Beach, and University oj 

 Calijornia School oJ Medicine, Los Angeles, California 



CHAPTER CONTENTS 



Anatomical Considerations 

 Reticulopctal Connections 

 Central Brain Stem 

 Rcticulofugal Projections 

 Ascending Influences 



Electrophysiological Characteristics 



Evoked potentials : sensory connections 



Evoked potentials : corticifugal connections 



Evoked potentials: cerebellum and basal ganglia 



Evoked potentials: neuronography 



Evoked potentials: conduction rates 



Evoked potentials: repetitive stimuli 



Microelectrode studies 



Cephalic conduction of RAS influence 

 Wakefulness and Sleep 



.\rousal response 



Prolonged wakefulness 

 Neurohumoral Reticular Mechanisms 

 Drug Effects 



Anesthesia 



Mood-altering drugs 

 Descending Influences 

 Inhibition 

 Facilitation 

 Suprascgmcntal Influences Upon Segmental Motor Neuron 



Activity 

 Reticulopctal Inputs to Reticular Formation 



Cerebral cortex 



Cerebellum 



Vestibular system 



Basal ganglia 



Sensory inputs 

 Spasticity 



Paraplegia 



Akinetic mutism 

 Tremor 

 Autonomic Mechanisms Mediated by Reticular Formation 

 Influence of Reticular Formation Upon Sensation 



PERHAPS IT IS WELL TO REMEMBER tVom lime to time 

 tliat the living organism from ameba to man is a 

 single unit and not a collection of systems. These or- 

 ganisms, regardless of station in the phylogenetic 

 scale, must react successfully to surrounding environ- 

 ments if they are to continue to exist. In the simplest 

 orders, no nervous .system is necessary but, with de- 

 veloping complexity of structure and function, a 

 system is appended for relating to each other the 

 several living processes. This appendage in man is a 

 highly prosencephalized brain; and in order to unify 

 the individual activities of its lo billion neurons into 

 appropriate patterns of functions, systems of control 

 have developed. 



It now appears likely that the brain-stem reticular 

 formation represents one of the more important inte- 

 grating structures if not, indeed, the master control 

 mechanism in the central nervous system. Neuron 

 combinations here long have been known to mediate 

 the control of many visceral functions such as respira- 

 tion, vasomotor tone and gastrointestinal secretion, 

 and in recent years investigations have indicated par- 

 ticipation of this region in neural processes subserving 

 temperature regulation and neuroendocrine control. 

 Furthennore, information has been adduced recently 

 which assigns to the reticular formation a major role 

 in the mediation of three more general neural func- 

 tions. First, it is known to be implicated in the arousal 

 response and wakefulness. Second, it exerts a critical 

 degree of influence over motor functions concerned 

 in phasic and tonic muscular control. Third, the cen- 

 tral brain stem is capable of modifying the reception, 

 conduction and integration of all sensory signals to 

 the degree that some will be perceived and others 

 rejected by the nervous system. This chapter will ex- 



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