As the name suggests, interneurons are the ones in between - they connect spinal motor and sensory neurons. As well as transferring signals between sensory and motor neurons, interneurons can also communicate with each other, forming circuits of various complexity.
They are multipolar, just like motor neurons. In the brain, the distinction between types of neurons is much more complex. Certainly, there are brain neurons involved in sensory processing — like those in visual or auditory cortex — and others involved in motor processing — like those in the cerebellum or motor cortex. However, within any of these sensory or motor regions, there are tens or even hundreds of different types of neurons. In fact, researchers are still trying to devise a way to neatly classify the huge variety of neurons that exist in the brain.
Looking at which neurotransmitter a neuron uses is one way that could be a useful for classifying neurons. However, within categories we can find further distinctions. Some GABA neurons, for example, send their axon mostly to the cell bodies of other neurons; others prefer to target the dendrites. Furthermore, these different neurons have different electrical properties, different shapes, different genes expressed, different projection patterns and receive different inputs.
Neurons classified by structure. Click to enlarge Credit: Ferris Jabr. Scientists have classified neurons into four main groups based on differences in shape. Multipolar neurons are the most common neuron in the vertebrate nervous system and their structure most closely matches that of the model neuron: a cell body from which emerges a single long axon as well as a crown of many shorter branching dendrites.
Unipolar neurons, the most common invertebrate neuron, feature a single primary projection that functions as both axon and dendrites.
Bipolar neurons usually inhabit sensory organs like the eye and nose. Their dendrites ferry signals from those organs to the cell body and their axons send signals from the cell body to the brain and spinal cord. Pseudo-unipolar neurons, a variant of bipolar neurons that sense pressure, touch and pain, have no true dendrites. Instead, a single axon emerges from the cell body and heads in two opposite directions, one end heading for the skin, joints and muscle and the other end traveling to the spinal cord.
Neurons classified by function. Researchers also categorize neurons by function. Sensory neurons collect information from sensory organs—from the eyes, nose , tongue and skin, for example.
Motor neurons carry signals from the brain and spinal cord to muscles. Interneurons connect one neuron to another: the long axons of projection interneuons link distant brain regions; the shorter axons of local interneurons form smaller circuits between neighboring cells. Do these basic classes account for all types of neurons? Well, just about every neuron in the human nervous system should fall into one these broad categories—but these categories do not capture the true diversity of the nervous system.
Not even close. If you really want to catalogue neurons in their many forms—somewhat like the way scientists have classed living things into families and species and subspecies—you're going to need a lot more categories. Neurons differ from one another structurally, functionally and genetically, as well as in how they form connections with other cells.
In some ways, it's up to you how far you want to take this. Some people are content with a few broad categories and do not see a need to identify and categorize every single type of neuron. Others are fascinated by the differences between cells in the brain and nervous system, even the subtlest distinctions.
Some are fascinated for practical reasons, because some of these differences help explain, for example, why certain diseases only harm a certain population of neurons. Neuron 92 , — Chen, K. Spatially resolved, highly multiplexed RNA profiling in single cells.
Science , aaa Moffitt, J. High-throughput single-cell gene-expression profiling with multiplexed error-robust fluorescence in situ hybridization. Natl Acad. USA , — High-performance multiplexed fluorescence in situ hybridization in culture and tissue with matrix imprinting and clearing. Chen, F. Nanoscale imaging of RNA with expansion microscopy. Methods 13 , — Lee, J.
Highly multiplexed subcellular RNA sequencing in situ. Ke, R. In situ sequencing for RNA analysis in preserved tissue and cells. Larsson, C. In situ detection and genotyping of individual mRNA molecules. Methods 7 , — The neuronal organization of the retina. Neuron 76 , — Design principles of insect and vertebrate visual systems. Neuron 66 , 15—36 Kay, J. Reese, B. Design principles and developmental mechanisms underlying retinal mosaics. Euler, T. Retinal bipolar cells: elementary building blocks of vision.
Franke, K. Inhibition decorrelates visual feature representations in the inner retina. This paper uses high-throughput calcium imaging to provide a physiological classification of retinal BCs; the types defined here correspond with those defined molecularly Ref. Wassle, H. Cone contacts, mosaics, and territories of bipolar cells in the mouse retina. Della Santina, L. Glutamatergic monopolar interneurons provide a novel pathway of excitation in the mouse retina.
Glasser, M. A multi-modal parcellation of human cerebral cortex. Douglas, R. Neuronal circuits of the neocortex. Greig, L. Molecular logic of neocortical projection neuron specification, development and diversity. Harris, K. The neocortical circuit: themes and variations. An updated review of neocortical neuronal types and their patterns of input-output connections, which are repeated across cortical areas. Molyneaux, B.
Neuronal subtype specification in the cerebral cortex. Kim, E. Three types of cortical layer 5 neurons that differ in brain-wide connectivity and function. Neuron 88 , — Kita, T. The subthalamic nucleus is one of multiple innervation sites for long-range corticofugal axons: a single-axon tracing study in the rat.
Velez-Fort, M. The stimulus selectivity and connectivity of layer six principal cells reveals cortical microcircuits underlying visual processing. Yamashita, T. Membrane potential dynamics of neocortical projection neurons driving target-specific signals.
Tasic, B. Adult mouse cortical cell taxonomy revealed by single cell transcriptomics. This article reports a comprehensive scRNA-seq characterization and classification of adult neocortical neurons using the Smart-seq method, which resulted in a transcriptomic cell type taxonomy that is supported by genetic Cre recombinase driver lines , physiological, morphological and projectional evidence. Kepecs, A. Interneuron cell types are fit to function.
Rudy, B. Tremblay, R. GABAergic interneurons in the neocortex: from cellular properties to circuits. An updated review of neocortical interneuron types, their cellular properties and their potential functions in circuit motifs and network operations. Klausberger, T. Neuronal diversity and temporal dynamics: the unity of hippocampal circuit operations.
Science , 53—57 Jiang, X. Principles of connectivity among morphologically defined cell types in adult neocortex. Science , aac Reports a large-scale electrophysiological and morphological characterization of adult neocortical neurons, revealing connectivity patterns among morphologically defined neuronal types. Ohki, K. Specificity and randomness in the visual cortex. Morrie, R. Development of synaptic connectivity in the retinal direction selective circuit.
Oyster, C. Direction-selective units in rabbit retina: distribution of preferred directions. Reid, R. From functional architecture to functional connectomics.
Neuron 75 , — Dehorter, N. Tuning of fast-spiking interneuron properties by an activity-dependent transcriptional switch. Spitzer, N. Neurotransmitter switching?
No surprise. Neuron 86 , — Gray, K. A review of the new HGNC gene family resource. McDonald, A. Nucleic Acids Res. Hamann, J. International Union of Basic and Clinical Pharmacology. Adhesion G protein-coupled receptors. Usoskin, D. Unbiased classification of sensory neuron types by large-scale single-cell RNA sequencing. Zeisel, A. Brain structure. Cell types in the mouse cortex and hippocampus revealed by single-cell RNA-seq. Darmanis, S. A survey of human brain transcriptome diversity at the single cell level.
Molecular identity of human outer radial glia during cortical development. Cell , 55—67 Romanov, R. Molecular interrogation of hypothalamic organization reveals distinct dopamine neuronal subtypes.
Li, C. Somatosensory neuron types identified by high-coverage single-cell RNA-sequencing and functional heterogeneity. Cell Res. Kee, N. Single-cell analysis reveals a close relationship between differentiating dopamine and subthalamic nucleus neuronal lineages. Cell Stem Cell 20 , 29—40 Campbell, J. A molecular census of arcuate hypothalamus and median eminence cell types.
Three major groups arise from this classification: multipolar , bipolar, and unipolar neurons. Multipolar neurons are defined as having three or more processes that extend out from the cell body. Title: Neurons uni bi multi pseudouni. Structural classification of neurons. Bipolar neurons have only two processes that extend in opposite directions from the cell body.
One process is called a dendrite, and another process is called the axon. Although rare, these are found in the retina of the eye and the olfactory system. Unipolar neurons have a single, short process that extends from the cell body and then branches into two more processes that extend in opposite directions.
The process that extends peripherally is known as the peripheral process and is associated with sensory reception. The process that extends toward the CNS is the central process. Unipolar neurons are found primarily in the afferent division of the PNS.
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