Within sensory, motor, and interneurons, there are different types of neurotransmitters and receptors that affect the nature of signal processing. Īs vast as the structural diversity is, there is an even greater diversity of functional properties. Indeed, recent work has established quantitative morphological distinctions across different cell types, focusing on quantities such as mean dendritic length, total dendritic length, and number of branching points. Modern techniques and devices have allowed for more precise quantitative measurements at the single-cell level. For instance, Santiago Ramón y Cajal’s “Histology of the Nervous System of Man and Vertebrates” is considered to be the founding document of neurobiology, consisting of detailed drawings and comparative descriptive analysis of neuron morphology across different cell types and species. Seminal studies in neuroscience characterized morphological differences across cell types. Different types of cells exhibit diverse morphological forms - some neurons have no axons or dendrites, while some have long axon processes that extend over meters, and others have vast dendritic trees that branch extensively to fill two- or three-dimensional space, corresponding to the mathematical and modeling concept known as space-filling. The processes form synaptic connections with one another in complex patterns. These dendrites generally conduct signals from the synapse to the cell body. Axons generally conduct signals from the cell body to the synapses, where they connect with the dendrites of other neurons. These processes transfer information between cells in the form of electrical and chemical signals. They are made up of a centralized cell body, called the soma, and two types of extending processes, axons and dendrites. Neurons are fundamental structural units of information processing and communication in animals. Moreover, using our mathematical model, we find that the conduction time delay of electrical signals systematically varies with species body size - neurons in larger species have longer delays - providing a possible explanation for hemispheric specialization in larger animals. We find that differences in structure between axons and dendrites as well as between dendrites of different cell types can be related to differences in function and associated evolutionary pressures. Based on theory for structure of and flow through biological resource distribution networks, we develop a new model that relates neuron structure to function. Previous studies of the differences among neuron cell types have focused on comparisons of either structure or function separately, without considering combined effects. They consist of a centralized cell body and two types of processes - axons and dendrites - that connect to one another. Our model also predicts a quarter-power scaling relationship between conduction time delay and species body size, which is supported by experimental data and may help explain the emergence of hemispheric specialization in larger animals as a means to offset longer time delays.Īuthor summary Neurons are the basic building blocks of the nervous system, responsible for information processing and communication in animals. Further comparison of different dendritic cell types reveals that Purkinje cell dendrite branching is constrained by material costs while motoneuron dendrite branching is constrained by conduction time delay over a range of species. Notably, our findings reveal that the branching of axons and peripheral nervous system neurons is mainly determined by time minimization, while dendritic branching is mainly determined by power minimization. We test our predictions for radius and length scale factors against those extracted from neuronal images, measured for cell types and species that range from insects to whales. Specifically, based on these principles, we use undetermined Lagrange multipliers to predict scaling ratios for axon and dendrite sizes across branching levels. Here, by constructing new biophysical theory and testing against our empirical measures of branching structure, we establish a correspondence between neuron structure and function as mediated by principles such as time or power minimization for information processing as well as spatial constraints for forming connections. Classifying neurons according to differences in structure or function is a fundamental part of neuroscience. Neurons are connected by complex branching processes - axons and dendrites - that collectively process information for organisms to respond to their environment.
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