# Neuron
A neuron (also called a nerve cell) is an electrically excitable cell that receives, generates, and transmits signals, and it is the basic functional unit of the nervous system[1](https://www.ncbi.nlm.nih.gov/books/NBK20367/). Neural signaling begins with an electrical impulse passed down the length of one neuron and continues with chemical signals exchanged at synaptic connections between nerve cells[2](https://www.ncbi.nlm.nih.gov/books/NBK10882/). Neurons work alongside glial cells, which outnumber nerve cells in the brain by a ratio of perhaps 3 to 1 and modulate neuronal signaling rather than generating it[3](https://www.ncbi.nlm.nih.gov/books/NBK10869/) • [4](https://pmc.ncbi.nlm.nih.gov/articles/PMC4739659/).
| Key fact | Detail |
|---|---|
| Definition | The basic functional unit of the nervous system; generates electrical impulses and communicates through synapses[1](https://www.ncbi.nlm.nih.gov/books/NBK20367/) • [2](https://www.ncbi.nlm.nih.gov/books/NBK10882/) |
| Main parts | Dendrites, cell body (soma), and axon; dendritic number varies from the single branched process of the pseudo-unipolar dorsal root ganglion neuron to the elaborate arbor of the cerebellar Purkinje cell[5](https://www.ncbi.nlm.nih.gov/books/NBK28104/) |
| Signaling | An action potential, a brief reversal of the resting membrane potential, carries the signal from dendrite to axon terminal; voltage-gated calcium channels then open and trigger neurotransmitter release[6](https://openstax.org/books/biology-2e/pages/35-2-how-neurons-communicate) |
| Myelinated conduction | Nodes of Ranvier, myelin-free axonal segments rich in Na+ channels, allow saltatory conduction of action potentials[7](https://www.nature.com/articles/nrn1253) |
| Neuron doctrine | Established by Santiago Ramón y Cajal using Camillo Golgi's staining method; both shared the 1906 Nobel Prize in Physiology or Medicine[8](https://www.nobelprize.org/stories/cells-nerves-genes/) |
| Diversity | A 2018 Allen Institute study sorted nearly 24,000 mouse cortical cells into 133 cell types based on gene expression[9](https://alleninstitute.org/news/a-comprehensive-parts-list-of-the-brain-built-from-its-components-the-cells) |
| Glial partners | Astrocytes, oligodendrocytes, microglia, and Schwann cells maintain the ionic milieu, form myelin, and control neurotransmitter uptake[3](https://www.ncbi.nlm.nih.gov/books/NBK10869/) |
## Structure
A neuron is a polarized cell with three characteristic regions. Dendrites receive inputs, the cell body contains the nucleus and other organelles essential to function, and the axon carries outgoing signals to terminals that form synapses with target cells[1](https://www.ncbi.nlm.nih.gov/books/NBK20367/) • [6](https://openstax.org/books/biology-2e/pages/35-2-how-neurons-communicate). The number and shape of dendrites vary with neuron type, ranging from the single branched process of the dorsal root ganglion pseudo-unipolar neuron, through the elaborate branching dendrite of the [Purkinje cell](https://www.edgepedia.org/purkinje-cell), to multipolar motor neurons with both apical and basal dendritic arbors[5](https://www.ncbi.nlm.nih.gov/books/NBK28104/).
**Cytoskeleton.** A dynamic neuronal cytoskeleton maintains the polarized morphology by assembling and targeting cytoskeletal, cytoplasmic, and membranous elements to the correct domains. Its biochemical composition differs strikingly between regions: the protein makeup of the axon differs significantly from that of cell bodies and dendrites, and there is diversity even along the length of a single axon[5](https://www.ncbi.nlm.nih.gov/books/NBK28104/).
## Signaling
Transmission within a neuron, from dendrite to axon terminal, is carried by the action potential, a brief reversal of the resting membrane potential. When neurotransmitter molecules bind to receptors on a neuron's dendrites, ion channels open; at the axon terminal, the arriving action potential opens voltage-gated calcium channels, allowing calcium to enter and triggering neurotransmitter release onto the next cell[6](https://openstax.org/books/biology-2e/pages/35-2-how-neurons-communicate). A neuron's excitation and inhibition depend on ion channels, which control the passage of small ions, most notably sodium, calcium, potassium, and chloride, in a selective manner.[10](https://www.ncbi.nlm.nih.gov/books/NBK234381/pdf/Bookshelf_NBK234381.pdf)
**Myelination and speed.** In myelinated axons, the nodes of Ranvier, specialized axonal segments that lack myelin, are rich in Na+ channels crucial for action potential conduction, along with adhesion molecules and cytoskeletal adaptor proteins such as ankyrin G and spectrin βIV. This local differentiation is tightly regulated by oligodendrocytes in the central nervous system and myelinating Schwann cells in the periphery, and it permits saltatory conduction, in which the impulse jumps between nodes[7](https://www.nature.com/articles/nrn1253).
**Axons as processors.** Axons are generally regarded as reliable transmission cables, but selective failure of action-potential propagation in axons can regulate communication with postsynaptic neurons, giving axons a computational role in the short-term dynamics of neural communication[11](https://www.nature.com/articles/nrn1397).
## Synapses
A synapse is the structure that permits a neuron to pass an electrical or chemical signal to another neuron or to a target effector cell[12](https://arxiv.org/abs/1906.01703). Synapses occur not only between axons and dendrites but also as axon-to-axon, dendrite-to-dendrite, and axon-to-cell-body contacts[6](https://openstax.org/books/biology-2e/pages/35-2-how-neurons-communicate). Synaptic strength can differ markedly from one synapse to the next, and different branches of the same neuron can evoke synaptic responses of diverse character in various follower cells[13](https://www.nature.com/articles/nrn876).
Mammalian synapses are molecularly complex structures composed of thousands of distinct proteins, and synaptic proteins are often expressed in variable patterns across brain regions and neuronal populations. Within each traditional neurotransmitter type, such as glutamatergic or GABAergic, there is deeper functional diversity in the strength, kinetics, voltage-dependence, and plasticity of transmission[14](https://www.nature.com/articles/nrn3170).
## Neuron types and classification
Neurons have diverse molecular, morphological, connectional, and functional properties. [Hongkui Zeng](https://www.edgepedia.org/hongkui-zeng), Executive Director of Structured Science at the [Allen Institute for Brain Science](https://www.edgepedia.org/allen-institute-for-brain-science), and [Joshua R. Sanes](https://www.edgepedia.org/joshua-r-sanes), a neurobiologist at Harvard University, argue in a 2017 review that grouping neurons into types is the only realistic way to manage this complexity, and that cell types must be defined by multiple criteria spanning morphology, physiology, molecular properties, and connections[15](https://www.nature.com/articles/nrn.2017.85).
**Transcriptomic censuses.** High-throughput single-cell methods have transformed this effort. In 2018, Allen Institute researchers analyzed genes from nearly 24,000 of the mouse's roughly 100 million brain cells and sorted cortical cells into 133 cell types, uncovering many rare types; a companion study then linked two newly identified neuron types in motor cortex to distinct roles, one in planning movements and the other in triggering movement[9](https://alleninstitute.org/news/a-comprehensive-parts-list-of-the-brain-built-from-its-components-the-cells). The NIH BRAIN Initiative made discovering brain cell types its first scientific priority, and its Cell Census Network and Cell Atlas Network (BICAN) now build reference atlases of brain cell types in human, non-human primate, and mouse across the lifespan, supported by eleven grants projected to total $100 million annually over 5 years[16](https://www.nih.gov/brain/research/tools-technologies-brain-cells-circuits/brain-initiative-cell-atlas-network).
Inhibitory neurons illustrate the granularity involved. Cortical GABAergic neurons show phenotypic diversity that underlies their functional versatility in shaping circuit operations, and recent high-throughput single-cell analyses of transcriptomes, morphology, and electrophysiology support defining cardinal interneuron types by their synaptic communication properties, encoded in transcriptional signatures[17](https://pubmed.ncbi.nlm.nih.gov/31222186/).
## Neuron-glia interactions
Glia were long viewed as supportive tissue, but that view has shifted to include roles in regulating complex behaviors. Astrocytes, the most abundant glial cells in the central nervous system, modulate synaptic function through gliotransmitter-mediated neurotransmitter reuptake, influencing neuronal signaling and behavior; microglia contribute to learning and memory processes, with microglial reductions affecting these functions in a developmentally dependent manner[18](https://pubmed.ncbi.nlm.nih.gov/39358030/). Established glial roles include maintaining the ionic milieu of nerve cells, modulating the rate of nerve signal propagation, controlling neurotransmitter uptake at synapses, providing a scaffold for neural development, and aiding or preventing recovery from neural injury[3](https://www.ncbi.nlm.nih.gov/books/NBK10869/).
**Myelin plasticity.** Plasticity is not confined to synapses. Recent work shows that sensory experience and learning drive plasticity in the oligodendrocyte lineage and the myelin sheaths these cells produce, a form of plasticity that plays a crucial role in learning and memory and has been implicated in neurodevelopmental disorders with cognitive symptoms[19](https://www.nature.com/articles/s41583-020-00379-8).
## History
The modern concept of the neuron rests on the neuron doctrine, the theory that the nervous system consists of discrete cells rather than a continuous network. [Santiago Ramón y Cajal](https://www.edgepedia.org/santiago-ramon-y-cajal) (1852–1934), using the "black reaction" staining method that [Camillo Golgi](https://www.edgepedia.org/camillo-golgi) (1843–1926) first documented in 1873, argued that neurons interact by contiguity rather than continuity, with conduction proceeding from dendrites and cell body to axon and its terminals[20](https://pmc.ncbi.nlm.nih.gov/articles/PMC2235197/). The two shared the 1906 [Nobel Prize in Physiology or Medicine](https://www.edgepedia.org/nobel-prize-in-physiology-or-medicine) "in recognition of their work on the structure of the nervous system," despite defending conflicting theories, Cajal's neuron doctrine and Golgi's reticular doctrine[8](https://www.nobelprize.org/stories/cells-nerves-genes/) • [21](https://www.sciencedirect.com/science/article/pii/S0165017307000574). The name neuron itself was coined by Heinrich Wilhelm Gottfried von Waldeyer-Hartz[22](https://www.sciencedirect.com/science/article/pii/S0960982206012036), and Charles Sherrington introduced the term synapse in 1897, referring to the Greek word for clasp; the debate between the doctrines was resolved decades later when electron microscopy visualized the synaptic cleft[23](https://escholarship.mcgill.ca/downloads/bv73c3894?locale=en).
**Modern circuit mapping.** The connectomic scale of this program has grown accordingly: a 2025 study published in Nature reconstructed the wiring connecting 84,000 neurons through roughly 500 million synapses in a piece of mouse visual cortex about the size of a poppy seed, using a mouse that watched clips from *The Matrix*, and released the 3D dataset openly[24](https://apnews.com/article/1a4e9db0a86c082e10da9c154546c592).
## References
1. [Information about the Brain, NIH Curriculum Supplement Series, NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK20367/)
2. [Neural Signaling, Neuroscience, NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK10882/)
3. [Neuroglial Cells, Neuroscience, NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK10869/)
4. [Glial Contributions to Neural Function and Disease, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC4739659/)
5. [Ultrastructure and Molecular Organization of Neurons and Glia, Basic Neurochemistry, NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK28104/)
6. [How Neurons Communicate, Biology 2e, OpenStax](https://openstax.org/books/biology-2e/pages/35-2-how-neurons-communicate)
7. [The local differentiation of myelinated axons at nodes of Ranvier, Nature Reviews Neuroscience (2003)](https://www.nature.com/articles/nrn1253)
8. [Exploring life's smallest details, NobelPrize.org](https://www.nobelprize.org/stories/cells-nerves-genes/)
9. [A comprehensive 'parts list' of the brain built from its components, the cells, Allen Institute (2018)](https://alleninstitute.org/news/a-comprehensive-parts-list-of-the-brain-built-from-its-components-the-cells)
10. [Mapping the Brain and Its Functions, NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK234381/pdf/Bookshelf_NBK234381.pdf)
11. [Information processing in the axon, Nature Reviews Neuroscience (2004)](https://www.nature.com/articles/nrn1397)
12. [Basic Neural Units of the Brain: Neurons, Synapses and Action Potential, arXiv (2019)](https://arxiv.org/abs/1906.01703)
13. [Diversification of synaptic strength: presynaptic elements, Nature Reviews Neuroscience (2002)](https://www.nature.com/articles/nrn876)
14. [Deep molecular diversity of mammalian synapses, Nature Reviews Neuroscience (2012)](https://www.nature.com/articles/nrn3170)
15. [Neuronal cell-type classification: challenges, opportunities and the path forward, Nature Reviews Neuroscience (2017)](https://www.nature.com/articles/nrn.2017.85)
16. [BRAIN Initiative Cell Atlas Network, NIH](https://www.nih.gov/brain/research/tools-technologies-brain-cells-circuits/brain-initiative-cell-atlas-network)
17. [The diversity of GABAergic neurons and neural communication elements, PubMed](https://pubmed.ncbi.nlm.nih.gov/31222186/)
18. [Neuron-Glial Interactions: Implications for Plasticity, Behavior, and Cognition, PubMed](https://pubmed.ncbi.nlm.nih.gov/39358030/)
19. [Myelin plasticity: sculpting circuits in learning and memory, Nature Reviews Neuroscience (2020)](https://www.nature.com/articles/s41583-020-00379-8)
20. [Introduction to A Century of Neuroscience Discovery, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC2235197/)
21. [A historical reflection of the contributions of Cajal and Golgi, ScienceDirect](https://www.sciencedirect.com/science/article/pii/S0165017307000574)
22. [Golgi and Cajal: The neuron doctrine and the 100th anniversary of the 1906 Nobel Prize, ScienceDirect](https://www.sciencedirect.com/science/article/pii/S0960982206012036)
23. [Cajal, the neuron doctrine, and the synapse, McGill eScholarship](https://escholarship.mcgill.ca/downloads/bv73c3894?locale=en)
24. [Scientists map part of a mouse's brain that's so complex it looks like a galaxy, AP News (2025)](https://apnews.com/article/1a4e9db0a86c082e10da9c154546c592)
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*Topic: Encyclopedia › Life and health › Biological foundations › Cell biology › Cell biology overview › Cell theory and outlines*
*Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license