Neuromorphology
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Neuromorphology (from Greek νεῦρον, neuron, "nerve"; μορφή, morphé, "form"; -λογία, -logia, “study of”) is the study of
nervous system In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes th ...
form, shape, and structure. The study involves looking at a particular part of the nervous system from a
molecular A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...
and
cellular Cellular may refer to: *Cellular automaton, a model in discrete mathematics * Cell biology, the evaluation of cells work and more * ''Cellular'' (film), a 2004 movie *Cellular frequencies, assigned to networks operating in cellular RF bands *Cell ...
level and connecting it to a
physiological Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
and
anatomical Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having it ...
point of view. The field also explores the communications and interactions within and between each specialized section of the nervous system.
Morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...
is distinct from
morphogenesis Morphogenesis (from the Greek ''morphê'' shape and ''genesis'' creation, literally "the generation of form") is the biological process that causes a cell, tissue or organism to develop its shape. It is one of three fundamental aspects of devel ...
. 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 Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
as the basic unit of life before researchers could agree upon the shape of a
neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...
. It was originally thought to be an independent globular corpuscle suspended along
nerve fibers A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...
that looped and coiled. It was not until the first successful microdissection of a whole nerve cell by
Otto Deiters Otto Friedrich Karl Deiters (; 15 November 1834 – 5 December 1863) was a German neuroanatomist. He was born in Bonn, studied at the University of Bonn, and spent most of his professional career in Bonn. He is remembered for his microscopic ...
in 1865 that the separate
dendrite Dendrites (from Greek δένδρον ''déndron'', "tree"), also dendrons, are branched protoplasmic extensions of a nerve cell that propagate the electrochemical stimulation received from other neural cells to the cell body, or soma, of the n ...
s and
axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action po ...
could be distinguished. At the end of the 19th century, new techniques, such as
Golgi's method Golgi's method is a silver staining technique that is used to visualize nervous tissue under light microscopy. The method was discovered by Camillo Golgi, an Italian physician and scientist, who published the first picture made with the technique ...
, 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
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
l
ganglion cell {{stack, A ganglion cell is a cell found in a ganglion. Examples of ganglion cells include: * Retinal ganglion cell (RGC) found in the ganglion cell layer of the retina * Cells that reside in the adrenal medulla, where they are involved in the s ...
s 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 Neuromodulation is the physiology, physiological process by which a given neuron uses one or more chemicals to regulate diverse populations of neurons. Neuromodulators typically bind to metabotropic receptor, metabotropic, G protein-coupled recep ...
, a process that involves electrochemical interactions from the whole
cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...
. 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 In science and engineering, an intrinsic property is a property of a specified subject that exists itself or within the subject. An extrinsic property is not essential or inherent to the subject that is being characterized. For example, mass ...
and
extrinsic In science and engineering, an intrinsic property is a property of a specified subject that exists itself or within the subject. An extrinsic property is not essential or inherent to the subject that is being characterized. For example, mass ...
factors. The neuromorphology of
nervous tissue Nervous tissue, also called neural tissue, is the main tissue component of the nervous system. The nervous system regulates and controls body functions and activity. It consists of two parts: the central nervous system (CNS) comprising the brain ...
is dependent upon genes and other factors, such as
electric fields Electric Fields are an Aboriginal Australian electronic music duo made up of vocalist Zaachariaha Fielding and keyboard player and producer Michael Ross. Electric Fields combine modern electric-soul music with Aboriginal culture and sing in Pi ...
, ionic waves, and
gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
. Developing cells additionally impose geometrical and physical constraints upon each other. These interactions affect the neural shape and
synaptogenesis Synaptogenesis is the formation of synapses between neurons in the nervous system. Although it occurs throughout a healthy person's lifespan, an explosion of synapse formation occurs during early brain development, known as exuberant synaptogenes ...
. 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 Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outco ...
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 Camillo Golgi (; 7 July 184321 January 1926) was an Italian biologist and pathologist known for his works on the central nervous system. He studied medicine at the University of Pavia (where he later spent most of his professional career) betwee ...
grouped neurons into type I and type II cells.
Golgi I In neuroscience, Golgi cells are inhibitory interneurons found within the granular layer of the cerebellum. They were first identified as inhibitory in 1964. It was also the first example of an inhibitory feedback network, where the inhibitory i ...
neurons have long axons that can move signals over long distances, such as in
Purkinje cells Purkinje cells, or Purkinje neurons, are a class of GABAergic inhibitory neurons located in the cerebellum. They are named after their discoverer, Czech anatomist Jan Evangelista Purkyně, who characterized the cells in 1839. Structure The ...
, whereas
Golgi II In neuroscience, Golgi cells are inhibitory interneurons found within the granular layer of the cerebellum. They were first identified as inhibitory in 1964. It was also the first example of an inhibitory feedback network, where the inhibitory in ...
neurons generally have shorter axons, such as
granule cell A granule is a large particle or grain. It can refer to: * Granule (cell biology), any of several submicroscopic structures, some with explicable origins, others noted only as cell type-specific features of unknown function ** Azurophilic granul ...
s, or are anoxonic. Neurons can be morphologically characterized as unipolar, bipolar, or multipolar. Unipolar and
pseudounipolar A pseudounipolar neuron is a type of neuron which has one extension from its cell body. This type of neuron contains an axon that has split into two branches. A single process arises from the cell body and then divides into an axon and a dendrite. ...
cells have only one
process A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process, activities that produce a specific se ...
extending from the cell body. Bipolar cells have a two processes extending from the
cell body The soma (pl. ''somata'' or ''somas''), perikaryon (pl. ''perikarya''), neurocyton, or cell body is the bulbous, non-process portion of a neuron or other brain cell type, containing the cell nucleus. The word 'soma' comes from the Greek '' σῶμ ...
and multipolar cells have three or more processes extending towards and away from the cell body.


Theoretical neuromorphology

Theoretical neuromorphology is a branch of neuromorphology focused on the mathematical description of the shape, structure and connectivity of the nervous system.


Gravitational neuromorphology

Gravitational neuromorphology studies the effects of altered
gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
on the architecture of the
central Central is an adjective usually referring to being in the center of some place or (mathematical) object. Central may also refer to: Directions and generalised locations * Central Africa, a region in the centre of Africa continent, also known as ...
,
peripheral A peripheral or peripheral device is an auxiliary device used to put information into and get information out of a computer. The term ''peripheral device'' refers to all hardware components that are attached to a computer and are controlled by the ...
, and
autonomic nervous system The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the peripheral nervous system that supplies viscera, internal organs, smooth muscle and glands. The autonomic nervous system is a control ...
s. This subfield aims to expand the current understanding of the adaptive capabilities of nervous systems, and specifically examines how environmental effects can alter nervous system structure and function. In this case environmental manipulations generally include exposing neurons to either
hypergravity Hypergravity is defined as the condition where the force of gravity exceeds that on the surface of the Earth. This is expressed as being greater than 1 '' g''. Hypergravity conditions are created on Earth for research on human physiology in a ...
or
microgravity The term micro-g environment (also μg, often referred to by the term microgravity) is more or less synonymous with the terms ''weightlessness'' and ''zero-g'', but emphasising that g-forces are never exactly zero—just very small (on the I ...
. It is a subset of gravitational biology.


Research methods and techniques

A variety of techniques have been used to study neuromorphology, including
confocal microscopy Confocal microscopy, most frequently confocal laser scanning microscopy (CLSM) or laser confocal scanning microscopy (LCSM), is an optical imaging technique for increasing optical resolution and contrast of a micrograph by means of using a sp ...
, design-based
stereology Stereology is the three-dimensional interpretation of two-dimensional cross section (geometry), cross sections of materials or tissues. It provides practical techniques for extracting quantitative information about a three-dimensional material from ...
, neuron tracing and neuron reconstruction. Current innovations and future research include
virtual microscopy Virtual microscopy is a method of posting microscope images on, and transmitting them over, computer networks. This allows independent viewing of images by large numbers of people in diverse locations. It involves a synthesis of microscopy technolo ...
, automated stereology,
cortical map Cortical maps are collections (areas) of minicolumns in the brain cortex that have been identified as performing a specific information processing function (texture maps, color maps, contour maps, etc.). Cortical maps Cortical organization, espe ...
ping, map guided automated neuron tracing, microwave techniques, and network analysis. Of the currently used techniques for studying neuromorphology, design-based stereology and confocal microscopy are the two most preferred methods. A complete database of neuronal morphology called the NeuroMorpho Database also exists.


Design-based stereology

Design-based stereology is one of the most prominent methods for mathematically extrapolating a 3-D form from a given 2-D form. It is currently the leading technique in
biomedical research Medical research (or biomedical research), also known as experimental medicine, encompasses a wide array of research, extending from "basic research" (also called ''bench science'' or ''bench research''), – involving fundamental scientif ...
for analyzing 3-D structures. Design-based stereology is a newer stereology technique that examines morphology that has been predefined and designed. This technique contrasts with the older method, model-based stereology, which utilized previously determined models as a guide. The more current design-based stereology allows researchers to probe the morphology of neurons without having to make assumptions about their size, shape, orientation or distribution. Design-based stereology also gives researchers more freedom and flexibility as model-based stereology is only effective if the models are truly representative of the object being studied, while design-based stereology is not constrained in this way.


Confocal microscopy

Confocal microscopy is the
microscopic The microscopic scale () is the scale of objects and events smaller than those that can easily be seen by the naked eye, requiring a lens (optics), lens or microscope to see them clearly. In physics, the microscopic scale is sometimes regarded a ...
procedure of choice for examining neuron structures as it produces sharp images with improved
resolution Resolution(s) may refer to: Common meanings * Resolution (debate), the statement which is debated in policy debate * Resolution (law), a written motion adopted by a deliberative body * New Year's resolution, a commitment that an individual mak ...
and decreased
signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to the noise power, often expressed in deci ...
. The specific way this microscopy works allows one to look at one confocal plane at a time, which is optimal when viewing neuronal structures. Other more conventional forms of microscopy simply do not allow one to visualize all neuronal structures, especially those that are subcellular. Recently, some researchers have actually been combining design-based stereology and confocal microscopy to further their investigations into the specific neuronal cellular structures.


Cortical mapping

Cortical map Cortical maps are collections (areas) of minicolumns in the brain cortex that have been identified as performing a specific information processing function (texture maps, color maps, contour maps, etc.). Cortical maps Cortical organization, espe ...
ping is defined as the process of characterizing specific regions in the brain based on either anatomical or functional features. Current brain atlases are not definitive or homogenous enough to portray specific structural details. Recent advances in functional brain imaging and
statistical analysis Statistical inference is the process of using data analysis to infer properties of an underlying distribution of probability.Upton, G., Cook, I. (2008) ''Oxford Dictionary of Statistics'', OUP. . Inferential statistical analysis infers propertie ...
may however prove to be sufficient in the future. A recent development in this field called the Gray Level Index (GLI) method allows for more objective identification of cortical regions via
algorithm In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific Computational problem, problems or to perform a computation. Algorithms are used as specificat ...
s. The GLI is a standardized method that allows researchers to determine neuron density. It is specifically defined as the ratio of area covered by Nissl-stained elements to area covered by unstained elements. More sophisticated cortical mapping techniques are still in the process of being developed and this field will most likely see an exponential growth in mapping methods in the near future.


Clinical applications

Neuromorphology has been used as a new method of exploring the underlying cause of many
neurological disorder A neurological disorder is any disorder of the nervous system. Structural, biochemical or electrical abnormalities in the brain, spinal cord or other nerves can result in a range of symptoms. Examples of symptoms include paralysis, muscle weakn ...
s, and has been included in the clinical study of various
neurodegenerative A neurodegenerative disease is caused by the progressive loss of structure or function of neurons, in the process known as neurodegeneration. Such neuronal damage may ultimately involve cell death. Neurodegenerative diseases include amyotrophic ...
diseases,
mental disorder A mental disorder, also referred to as a mental illness or psychiatric disorder, is a behavioral or mental pattern that causes significant distress or impairment of personal functioning. Such features may be persistent, relapsing and remitti ...
s,
learning disabilities Learning disability, learning disorder, or learning difficulty (British English) is a condition in the brain that causes difficulties comprehending or processing information and can be caused by several different factors. Given the "difficult ...
, and dysfunctions due to brain damage. Researchers have been using neuromorphological techniques to not only study the damage but also ways to regenerate the damage nerve through ways like axon growth stimulation. Neuromophology has been used to study
optical nerve In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived from ...
damage, specifically looking at
lesion A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals. Types There is no designated classifi ...
s and
atrophies Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations (which can destroy the gene to build up the organ), poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply ...
. Researchers have also examined and identified the neuromorphology of the human penis to better understand the role the sympathetic nervous system plays in achieving an erection.


Current and future research


Computational neuromorphology

Computational neuromorophology examines neurons and their substructures by cutting them into slices and studying these different subsections. It also describes the neuromorphological space as a 3-D space. This allows researchers to understand the size of specific neuronal components. Additionally, the 3-D imaging helps researchers comprehend how the neuron transmits information within itself.


Virtual microscopy

Virtual microscopy would allow researchers to obtain images with a decreased amount of imaging sessions, thus preserving the integrity of the tissue and decrease the possibility the
fluorescent dyes A fluorophore (or fluorochrome, similarly to a chromophore) is a fluorescent chemical compound that can re-emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with se ...
fading during imaging. This method would additionally give researchers abilities to visualize currently unobtainable data, such as rare cell types and the spatial allocation of cells in a specific brain region. Virtual microscopy would essentially allow for the
digitization DigitizationTech Target. (2011, April). Definition: digitization. ''WhatIs.com''. Retrieved December 15, 2021, from https://whatis.techtarget.com/definition/digitization is the process of converting information into a Digital data, digital (i ...
of all images obtained, therefore preventing deterioration of the data. This digitization could also potentially permit researchers to create a
database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases sp ...
to share and store their data.


See also

*
Cellular neuroscience Cellular neuroscience is a branch of neuroscience concerned with the study of neurons at a cellular level. This includes Morphology (biology), morphology and physiology, physiological properties of single neurons. Several techniques such as intrace ...
*
Morphology (biology) Morphology is a branch of biology dealing with the study of the form and structure of organisms and their specific structural features. This includes aspects of the outward appearance (shape, structure, colour, pattern, size), i.e. external mo ...
*
Theoretical neuromorphology Theoretical neuromorphology is the science of using morphology to mathematically describe the shape and the connectivity in the nervous system. History The rational study of shapes has been long to form. In the major progresses made during the la ...


References


External links


NeuroMorpho
{{DEFAULTSORT:Neuromorphology Neuroanatomy