CHAPTER X 



Identification and analysis of single unit activity 

 in the central nervous system 



KARL FRANK I N'llional Institute of Neurological Diseases and Blindness, 

 j National Institutes oj Health, Bethesda, Maryland 



CHAPTER CONTENTS 



Single Unit Techniques 

 Single Fiber Isolation 

 Microelectrodes 

 Metal electrodes 

 Micropipettes 

 Construction 

 Filling 



Electrical properties of micropipettes 

 Resistance 

 Capacitance 

 Tip potential 

 Frequency response 

 Amplifiers 

 Identification of Single Units 

 Position 

 Axons 



Damage to Penetrated Units 

 Primary Sensory Fibers 

 Motoneurons 

 Interneurons 

 Slow Potentials 



Steps in the Development of Cell Spikes 

 Stimulation Through Microelectrodes 



SOMEWHERE IN THE MIDDLE of the widc range of ap- 

 proaches to neurophysiology is the study of the 

 physiological properties of the individual neurons in 

 the central nervous system. In order to put this ap- 

 proach in its proper perspective, it should be empha- 

 sized that the functioning of the central nervous 

 system as a whole is as difficult to predict from the 

 known properties of each of its cellular components as 

 are the properties of the units from the behavior of 



the whole. While it is not sufficient for understanding 

 the nervous system, it is necessary to study the indi- 

 vidual nerve cells, their various structures, their differ- 

 ent patterns of activity and the mechanisms operat- 

 ing to yield and to limit such activity. 



A great body of knowledge has been built up about 

 the nature of neurons in the peripheral nervous 

 system. One of the most fruitful approaches to the 

 study of single units in the central nervous system is 

 through the extension and elaboration of these 

 peripheral findings. Properties of peripheral ner\-e 

 fibers, of sensory and motor end organs and of 

 ganglion cells are continually being dfscovered within 

 the spinal cord and brain, and these properties must 

 be carefully checked lest differences or totally new 

 mechanisms be thereby overlooked. 



Neurons show a variety of changes which can be 

 observed in a study of their activity. Optical, thermal 

 and mechanical changes have all been ob.served to 

 accompany activity in nerve, but chemical and 

 especially electrical changes have been used most 

 extensively to acquire our present knowledge of 

 single cell neurophysiology. 



SINGLE UNIT TECHNIQUES 



Techniques for single unit studies all require some 

 means of isolating the unit to be studied. Cells which 

 cannot be isolated anatomically due to their many 

 connections with other cells may sometimes be iso- 

 lated electrically. This may be done either by limit- 

 ing nervous activity at a particular time to the unit 



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