Neuromorphology (from Greek νεῦρον, neuron, "nerve"; μορφή, morphé, "form"; -λογία, -logia, “study of”) is the study of nervous system form, shape, and structure. The study involves looking at a particular part of the nervous system from a molecular and cellular level and connecting it to a physiological and anatomical point of view. The field also explores the communications and interactions within and between each specialized section of the nervous system. Morphology is distinct from morphogenesis. Morphology is the study of the shape and structure of biological organisms, while morphogenesis is the study of the biological development of the shape and structure of organisms. Therefore, neuromorphology focuses on the specifics of the structure of the nervous system and not the process by which the structure was developed. Neuromorphology and morphogenesis, while two different entities, are nonetheless closely linked.
History
Progress in defining the morphology of nerve cells has been slow in its development. It took nearly a century after the acceptance of the cell as the basic unit of life before researchers could agree upon the shape of a neuron. It was originally thought to be an independent globular corpuscle suspended along nerve fibers that looped and coiled. It was not until the first successful microdissection of a whole nerve cell by Otto Deiters in 1865 that the separate dendrites and axon could be distinguished. At the end of the 19th century, new techniques, such as Golgi's method, were developed that enabled researchers to view the whole neuron. This Golgi investigation then promoted new research in neuronal spacing by Ramon y Cajal in 1911. Further morphology research continued to develop, including dendritic morphology. In 1983 Thoroya Abdel-Maguid and David Bowsher expanded upon the golgi method and combined it with an impregnation technique which allowed them to visualize the dendrites of neurons and classify them based on their dendritic patterns. Since then, myriad techniques have been developed and applied to the field of neuromorphology.
Influence on neuron function
Research has supported a relationship between the morphological and functional properties of neurons. For instance, the accordance between the morphology and the functional classes of cat retinal ganglion cells has been studied to show the relationship between neuron shape and function. Orientation sensitivity and dendritic branching patterns are a few other common characteristics of neurons that researchers have noted as having an effect on neuron function. Ian A. Meinertzhagen et al. have recently established a connection between the genetic factors that underlie a specific neuronal structure and how these two factors then pertain to the neuron's function by examining the optic nerves in Drosophila melanogaster. They assert the structure of the neuron is able to determine its function by dictating synapse formation.
The geometry of neurons often depends on the cell type and the history of received stimuli that is processed through the synapses. The shape of a neuron often directs the neuron's function by establishing its synaptic partnerships. However, there is also a growing evidence for volume transmission, a process that involves electrochemical interactions from the whole cell membrane.
The axonal tree morphology is instrumental in activity modulation and information coding.
Development
The development of the morphological features of neurons is governed by both intrinsic and extrinsic factors. The neuromorphology of nervous tissue is dependent upon genes and other factors, such as electric fields, ionic waves, and gravity. Developing cells additionally impose geometrical and physical constraints upon each other. These interactions affect the neural shape and synaptogenesis. Morphological measures and imaging applications are important for further understanding the developmental process.
Subfields
General morphology
Since there is a broad range of functions performed by different types of neurons in diverse parts of the nervous system, there is a wide variety in the size, shape, and electrochemical properties of neurons. Neurons can be found in different shapes and sizes and can be classified based upon their morphology. The Italian scientist Camillo Golgi grouped neurons into type I and type II cells. Golgi type I neurons have long axons that can move signals over long distances, such as in Purkinje cells, whereas Golgi type II neurons generally have shorter axons, such as granule cells, or are anaxonic.