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A dendrite (from Greek δένδρον déndron, "tree") or dendron is a branched cytoplasmic process that extends from a nerve cell that propagates the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project. Electrical stimulation is transmitted onto dendrites by upstream neurons (usually via their ) via which are located at various points throughout the dendritic tree.
Dendrites play a critical role in integrating these synaptic inputs and in determining the extent to which are produced by the neuron.
Synaptic activity causes local changes in the electrical potential across the plasma membrane of the dendrite. This change in membrane potential will passively spread along the dendrite, but becomes weaker with distance without an action potential. To generate an action potential, many excitatory synapses have to be active at the same time, leading to strong depolarization of the dendrite and the cell body (soma). The action potential, which typically starts at the axon hillock, propagates down the length of the axon to the axon terminals where it triggers the release of neurotransmitters, but also backwards into the dendrite (retrograde propagation), providing an important signal for spike-timing-dependent plasticity (STDP).
Most are axodendritic, involving an axon signaling to a dendrite. There are also dendrodendritic synapses, signaling from one dendrite to another. (2025). 9780205239399, Pearson. ISBN 9780205239399 An autapse is a synapse in which the axon of one neuron transmits signals to its own dendrite.
The general structure of the dendrite is used to classify neurons into multipolar, Bipolar neuron and Unipolar neuron types. Multipolar neurons are composed of one axon and many dendritic trees. Pyramidal cells are multipolar cortical neurons with pyramid-shaped cell bodies and large dendrites that extend towards the surface of the cortex (apical dendrite). Bipolar neurons have two main dendrites at opposing ends of the cell body. Many inhibitory neurons have this morphology. Unipolar neurons, typical for insects, have a stalk that extends from the cell body that separates into two branches with one containing the dendrites and the other with the terminal buttons. In vertebrates, sensory neurons detecting touch or temperature are unipolar. (2025). 9780205832569, Allyn & Bacon. ISBN 9780205832569 Dendritic branching can be extensive and in some cases is sufficient to receive as many as 100,000 inputs to a single neuron.
Some of the first intracellular recordings in a nervous system were made in the late 1930s by Kenneth S. Cole and Howard J. Curtis. Swiss Rüdolf Albert von Kölliker and German Robert Remak were the first to identify and characterize the axonal initial segment. Alan Hodgkin and Andrew Huxley also employed the squid giant axon (1939) and by 1952 they had obtained a full quantitative description of the ionic basis of the action potential, leading to the formulation of the Hodgkin–Huxley model. Hodgkin and Huxley were awarded jointly the Nobel Prize for this work in 1963. The formulas detailing axonal conductance were extended to vertebrates in the Frankenhaeuser–Huxley equations. Louis-Antoine Ranvier was the first to describe the gaps or nodes found on axons and for this contribution these axonal features are now commonly referred to as the Nodes of Ranvier. Santiago Ramón y Cajal, a Spanish anatomist, proposed that axons were the output components of neurons. He also proposed that neurons were discrete cells that communicated with each other via specialized junctions, or spaces, between cells, now known as a synapse. Ramón y Cajal improved a silver staining process known as Golgi's method, which had been developed by his rival, Camillo Golgi.
Little is known about the process by which dendrites orient themselves in vivo and are compelled to create the intricate branching pattern unique to each specific neuronal class. One theory on the mechanism of dendritic arbor development is the synaptotropic hypothesis. The synaptotropic hypothesis proposes that input from a presynaptic to a postsynaptic cell (and maturation of excitatory synaptic inputs) eventually can change the course of synapse formation at dendritic and axonal arbors.
This synapse formation is required for the development of neuronal structure in the functioning brain. A balance between metabolic costs of dendritic elaboration and the need to cover the receptive field presumably determine the size and shape of dendrites. A complex array of extracellular and intracellular cues modulates dendrite development including transcription factors, receptor-ligand interactions, various signaling pathways, local translational machinery, cytoskeletal elements, Golgi outposts and endosomes. These contribute to the organization of the dendrites on individual cell bodies and the placement of these dendrites in the neuronal circuitry. For example, it was shown that β-actin zipcode binding protein 1 (ZBP1) contributes to proper dendritic branching.
Other important transcription factors involved in the morphology of dendrites include CUT, Abrupt, Collier, Spineless, ACJ6/drifter, CREST, NEUROD1, CREB, NEUROG2 etc. Secreted proteins and cell surface receptors include neurotrophins and tyrosine kinase receptors, BMP7, Wnt/dishevelled, EPHB 1–3, Semaphorin/plexin-neuropilin, slit-robo, netrin-frazzled, reelin. Rac, CDC42 and RhoA serve as cytoskeletal regulators, and the motor protein includes KIF5, dynein, LIS1. Dendritic arborization has been found to be induced in cerebellum Purkinje cells by substance P. Important secretory and endocytic pathways controlling the dendritic development include DAR3 /SAR1, DAR2/Sec23, DAR6/Rab1 etc. All these molecules interplay with each other in controlling dendritic morphogenesis including the acquisition of type specific dendritic arborization, the regulation of dendrite size and the organization of dendrites emanating from different neurons.
Branching morphologies may assume an adendritic structure (not having a branching structure, or not tree-like), or a tree-like radiation structure. Tree-like arborization patterns can be spindled (where two dendrites radiate from opposite poles of a cell body with few branches, Bipolar neuron ), spherical (where dendrites radiate in a part or in all directions from a cell body, see cerebellar granule cells), laminar (where dendrites can either radiate planarly, offset from cell body by one or more stems, or multi-planarly, see retinal horizontal cells, retinal ganglion cells, Amacrine cell respectively), cylindrical (where dendrites radiate in all directions in a cylinder, disk-like fashion, Globus pallidus), conical (dendrites radiate like a cone away from cell body, Pyramidal cell), or fanned (where dendrites radiate like a flat fan as in ).
Dendrites were once thought to merely convey electrical stimulation passively. This passive transmission means that voltage changes measured at the cell body are the result of activation of distal synapses propagating the electric signal towards the cell body without the aid of voltage-gated ion channels. Cable theory describes how voltage changes at a particular location on a dendrite transmit this electrical signal through a system of converging dendrite segments of different diameters, lengths, and electrical properties. Based on passive cable theory one can track how changes in a neuron's dendritic morphology impact the membrane voltage at the cell body, and thus how variation in dendrite architectures affects the overall output characteristics of the neuron. Dendrite radius has notable effects on resistance to electrical current, which in turn affects conduction time and speed. Dendrite branching optimizes of energy efficiency while maintaining functional connectivity by minimizing power and emphasizing effective signal transmission, supporting their roles in signal integration over longer times. This behavior seen in dendrites differs from that in axons, which give more priority to conduction time (and speed). Such tradeoffs influence overall neuronal structures, leading to a scaling relationship between conduction time and body size. (1999). 9780195104912, Oxford Univ. Press. ISBN 9780195104912 (2025). 9780198566564, Oxford University Press. ISBN 9780198566564
Action potentials initiated at the axon hillock propagate back into the dendritic arbor. These back-propagating action potentials depolarize the dendritic membrane and provide a crucial signal for synapse modulation and long-term potentiation. Back-propagation is not completely passive, but modulated by the presence of dendritic voltage-gated potassium channels. Furthermore, in certain types of neurons, a train of back-propagating action potentials can induce a calcium action potential (a dendritic spike) at dendritic initiation zones.
/ref> Neuronal dendrites have various compartments known as functional units that are able to compute incoming stimuli. These functional units are involved in processing input and are composed of the subdomains of dendrites such as spines, branches, or groupings of branches. Therefore, plasticity that leads to changes in the dendrite structure will affect communication and processing in the cell. During development, dendrite morphology is shaped by intrinsic programs within the cell's genome and extrinsic factors such as signals from other cells. But in adult life, extrinsic signals become more influential and cause more significant changes in dendrite structure compared to intrinsic signals during development. In females, the dendritic structure can change as a result of physiological conditions induced by hormones during periods such as pregnancy, lactation, and following the estrous cycle. This is particularly visible in pyramidal cells of the CA1 region of the hippocampus, where the density of dendrites can vary up to 30%.
Recent experimental observations suggest that adaptation is performed in the neuronal dendritic trees, where the timescale of adaptation was observed to be as low as several seconds. Certain machine learning architectures based on dendritic trees have been shown to simplify the learning algorithm without affecting performance.
The second function of dendritic trees in this regard is their ability to shape signal propagation that allows for sub-cellular compartmentalization. Large Depolarization can lead to local regenerative potentials, which may allow neurons to transition from stages of isolated dendritic events (segregation) to combined dendritic events (integration). Dendritic compartmentalization has implications in information processing, where it serves as a foundation of trans-neuron signaling, processing stimuli, computation, neuronal expressivity, and mitigating neuronal noise. Likewise, this phenomenon also underlies the storage of information by optimizing learning capacity and storage capacity. In other types of neurons, such as those of the medial superior olive, have differing dendritic properties that allow for coincidence detection. In contrast, in retinal ganglion cells, dendritic integration is used for computing directional selectivity, allowing neurons to respond to direction of movement. Therefore dendritic trees serve various purposes in integrating and processing various different types of stimuli and underly various neurological processes.
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