Neurons and Interneuronal Connections of the Central Visual System

This century has witnessed the creation of new sciences extending the frontiers of knowledge to an unprecedented degree. We have seen the birth of cybernetics and bionics, bringing together such apparently distantly related branches of science as neurohistology and automation, synaptology and electronics. The electron microscope has resolved tissues almost down to the molecular level, and histochemistry has led to the fine analysis of brain structure. However, before these and other new sciences can develop properly and scientifically, a precise knowledge of the structure of the material with which they are concerned is absolutely essential. That is why the need exists at the present time for a detailed study of the larger units, i. e. , the neurons, their interrelationships and the pathways by which excitation is conducted. Biologists, neurologists, physicists, and specialists in other technical disci plines will find this study highly useful. During recent years many advances have been made in knowledge of the central visual system and its pathways. Above all, it has been found that the visual system is very extensive. The optic tract is connected, not only with the lateral geniculate body, but with the superior colliculus and the pulvinar. Besides the discovery of these principal pathways, connections have also been studied with the hypothalamus, the pretectal region, the medial geniculate body, subthalamus, and other parts of the brain stem. The visual system is thus connected with the reflex apparatus, the autonomic nervous system, and the auditory and reticular systems.

Contenu

1. Neurons of the Central Visual System.- The Cortex and Lateral Geniculate Body.- Neuronal Structure of the Visual Cortex and Lateral Geniculate Body in Some Mammals.- Visual System of the Hedgehog (Insectivora).- Visual System of the Rabbit (Rodentia).- Visual System of the Dog (Carnivora).- Visual System of Monkeys (Primates).- Visual System of Man.- Size of the Neurons and Density of Their Arrangement.- Characteristics of the Layers of the Visual Cortex.- Similarities and Differences Between Neurons of Monkey and Man.- Distinctive Structural Features of Neurons in Areas 17, 18, and 19 of the Human Occipital Cortex.- 2. Connections Between Neurons and Details of Their Structure.- Endings and Branches of Axons.- Dendrites, Their Endings and Ramifications.- Varieties of Connections Between Neurons in the Cortical and Subcortical Parts of the Visual System.- Axo-dendritic Contacts of Cortical Pyramidal Cells.- Axo-somatic Connections of Cortical Pyramidal Cells.- Axo-dendritic Contacts of Cortical Stellate Cells.- Axo-somatic Contacts of Cortical Stellate Cells.- Axo-axonal Connections in the Cortex.- Axo-dendritic and Axo-somatic Contacts of Cells of the Lateral Geniculate Body.- Connections in the Retina.- Reality of the Systems of Spines on Dendrites; Their Origin and Role.- Structure of Interneuronal Connections in the Cortex.- 3. Differences in Structure and Connections of the Visual System at Cortical and Subcortical Levels.- The Cortical Level.- Connections of Pyramidal Cells and Their Significance.- Connections of the Long-Axon Star Cells of Cajal.- Connections of Short-Axon Stellate Cells and Their Significance.- The Subcortical Level.- Neurons of the Lateral Geniculate Body.- The Main Differences Between Neurons of the Visual Cortex and Lateral Geniculate Body.- 4. Structure of the Central Visual System and Pathways.- Cortical Analyzer and Diffuse Elements.- Efferent Connections of the Visual Cortex.- Centrifugal Connections of the Retina.- A Scheme of the Structure of the Visual System.- 5. Specificity of Structure of the Central Visual System.- Structure of Neurons of the Visual System and Their Comparison with Other Neurons.- Specificity of Structure in Relation to the Problem of Color Vision.- New Data on the Structure and Function of the Lateral Geniculate Body in Primates Relative to the Problem of Color Vision.