12 



Survey of Neurobiology 



from gross dissection of the interior of 

 the human brain. Rosett, and Krieg have 

 lately shown the possibilities in this by 

 different means. Comparative studies of 

 similar type would no doubt be fruitful. 



MICROSCOPIC MORPHOLOGY 



The significance of microscopic structure 

 for understanding of function in any tissue 

 became apparent with the establishment 

 of the cell "theory" by Schleiden and 

 Schwann a century ago. With the de- 

 velopment of staining methods specific 

 for nervous tissue by Golgi, Cajal and 

 others (arising out of the photographic 

 process of Daguerre) and the application 

 of the cell idea to nervous tissue in the 

 form of "the neuron concept," details of 

 the relationships of individual neurons to 

 each other began to be made available. 

 Needless to say, this mapping of the fun- 

 damental units of structure is not even 

 near completion for man's nervous system, 

 much less for that of numerous forms of 

 experimental animals of all types. 



There is much to be done of pure de- 

 scriptive character in practically every part 

 of the nervous system centrally. Why are 

 different nerve cells shaped as they are; 

 why are synapses variously formed as they 

 are; what is the exact relationship of two 

 neurons at synapses other than those only 

 so recently adequately described? Does 

 a "nerve net" as a true syncytial arrange- 

 ment of neurons ever occur? If so, in what 

 animals, and under what circumstances and 

 in what particular form? How is the mor- 

 phology of synapses related to the produc- 

 tion of humoral substances which are re- 

 lated to nerve impulse transmission? Why 

 does the Nissl material not occur in axons? 

 What is the significance of the various 

 forms of dendrites? Does the recent dem- 

 onstration that continuous protein syn- 

 thesis in the nerve cell under influence of 

 nuclear components, and the probable mi- 

 gration of new materials distalward along 

 the axon, complete the story — or only raise 

 more questions as to how the neuron sur- 

 vives throughout a long life without the 

 capacity for unit reproduction? These are 

 only a few of the questions which may be 



asked about the purely morphological de- 

 tails of neuron structure. 



Other parts of the nervous system not 

 made of neurons also require investigation. 

 What is the significance of the form of the 

 various glial types? Are there any more 

 than the three well known ones and the re- 

 cently included glial cell without pro- 

 cesses? What is their exact relationship to 

 neurons and other structures? What is the 

 significance of the rhythmic contraction of 

 certain glial cells demonstrated by motion 

 pictures in tissue culture? Do the satellite 

 and capsule cells of peripheral ganglia and 

 the neurilemmal cells bear the same rela- 

 tionship to peripheral structures? Even the 

 vascular supply of the nervous system, the 

 meninges and chorioid plexuses require 

 further investigation. It would be valuable 

 to know the structural and physiological 

 mechanism involved in the production and 

 maintenance of increased intracranial pres- 

 sure. 



In the periphery, what is the significance 

 to function of the various forms of nerve 

 terminations? How specific are the re- 

 quirements on the sensory side of both 

 special and general sense organs of the 

 non-neuronal constituents for the achieve- 

 ment of specific sensations? 



It would be interesting to know the 

 underlying morphology required which 

 allows the signalling of external stimuli so 

 that they are interpreted as heat, cold, 

 sound, etc. With all that is known of the 

 microscopic structure of the retina the ex- 

 periments of Hecht, which show that 5 to 8 

 quanta of light acting over an area con- 

 taining about 500 rods produce the minimal 

 sensation of vision, lead to a further de- 

 mand for knowledge of retinal structure. 



On the motor side what is the morpho- 

 logical relationship of motor endings to 

 skeletal muscle? Is a paraterminal network 

 once described in the neighborhood of 

 motor endings present or even necessary 

 with the accepted ideas of humoral trans- 

 mission? It would be valuable to know 

 the actual details of innervation of ordinary 

 cardiac muscle fibers and of the modified 

 ones of the atrio-ventricular bundle. 



The inadequacy of descriptions of in- 



