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Dendrites (from Greek dendron, “tree”) are the branched projections of a neuron that act to conduct the electrical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project. The soma, or cyton or perikaryon, is the bulbous end of a Neuron, containing the Cell nucleus. An axon or nerve fiber is a long slender projectionof a nerve cell or Neuron, that conducts electrical impulses away from the neuron's Cell In Cell biology, the nucleus (pl nuclei; from Latin la ''nucleus'' or la ''nuculeus'' "little nut" or kernel is a membrane-enclosed Nodes of Ranvier are known as the gaps (about 1 micrometer in diameter formed between myelin sheath cells along axons or nerve fibers Nodes of Ranvier are known as the gaps (about 1 micrometer in diameter formed between myelin sheath cells along axons or nerve fibers Chemical synapses are specialized junctions through which Neurons signal to each other and to non-neuronal cells such as those in Muscles or Glands Named after the German physiologist Theodor Schwann, Schwann cells (also referred to as neurolemmocytes) are a variety of Glial cell that mainly Myelin is an electrically-insulating Dielectric Phospholipid layer that surrounds only the Axons of many Neurons It is an outgrowth Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly Neurons (ˈnjuːɹɒn also known as neurones and nerve cells) are responsive cells in the Nervous system that process and transmit information The soma, or cyton or perikaryon, is the bulbous end of a Neuron, containing the Cell nucleus. Electrical stimulation is transmitted onto dendrites by upstream neurons via synapses which are located at various points throughout the dendritic arbor. Chemical synapses are specialized junctions through which Neurons signal to each other and to non-neuronal cells such as those in Muscles or Glands Dendrites play a critical role in integrating these synaptic inputs and in determining the extent to which action potentials are produced by the neuron. Chemical synapses are specialized junctions through which Neurons signal to each other and to non-neuronal cells such as those in Muscles or Glands In Neurophysiology, the action potential is a self-regenerating Wave of Electrochemical activity that allows Nerve cells to carry a signal
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Electrical properties of dendrites
The structure and branching of a neuron's dendrites, as well as the availability and variation in voltage-gated ion conductances, strongly influences how it integrates the input from other neurons, particularly those that input only weakly. Voltage-gated ion channels are a class of transmembrane Ion channels that are activated by changes in electrical Potential difference near the channel these This integration is both "temporal" -- involving the summation of stimuli that arrive in rapid succession -- as well as "spatial" -- entailing the aggregation of excitatory and inhibitory inputs from separate branches.
Dendrites were once believed to merely convey stimulation passively . In this example, voltage changes measured at the cell body result from activations of distal synapses propagating to the soma without the aid of voltage-gated ion channels. Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical Voltage-gated ion channels are a class of transmembrane Ion channels that are activated by changes in electrical Potential difference near the channel these Passive 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. Classical cable theory describes the development of mathematical models that can calculate the flow of electric current (and accompanying Voltage) along passive neuronal Based on passive cable theory one can track how changes in a neuron’s dendritic morphology changes the membrane voltage at the soma, and thus how variation in dendrite architectures affects the overall output characteristics of the neuron.
Although passive cable theory offers insights regarding input propagation along dendrite segments, it is important to remember that dendrite membranes are host to a cornucopia of proteins some of which may help amplify or attenuate synaptic input. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Sodium, calcium, and potassium channels are all implicated in contributing to input modulation. Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 Potassium (pəˈtæsiəm is a Chemical element. It has the symbol K (kalium from qalīy Atomic number 19 and Atomic mass 39 It is possible that each of these ion species has a family of channel types each with its own biophysical characteristics relevant to synaptic input modulation. An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge Such characteristics include the latency of channel opening, the electrical conductance of the ion pore, the activation voltage, and the activation duration. Latency is a time delay between the moment something is initiated and the moment one of its effects begins or becomes detectable Electrical conductance is a measure of how easily Electricity flows along a certain path through an Electrical element. In this way, a weak input from a distal synapse can be amplified by sodium and calcium currents en route to the soma so that the effects of distal synapse are no less robust than those of a proximal synapse.
One important feature of dendrites, endowed by their active voltage gated conductances, is their ability to send action potentials back into the dendritic arbor. Known as backpropagating action potentials, these signals depolarize the dendritic arbor and provide a crucial component toward synapse modulation and long-term potentiation. In Neuroscience, long-term potentiation ( LTP) is the long-lasting improvement in communication between two Neurons that results from stimulating them Furthermore, a train of backpropagating action potentials artificially generated at the soma can induce a calcium action potential at the dendritic initiation zone in certain types of neurons. Whether or not this mechanism is of physiological importance remains an open question.
Dendrite development
Despite the critical role that dendrites play in the computational tendencies of neurons, very 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. In vivo ( Latin: within the living means that which takes place inside an organism. It is likely that a complex array of extracellular and intracellular cues modulate dendrite development. In Cell biology, Molecular biology and related fields the word extracellular (or sometimes extracellular space) means "outside the cell Not to be confused with Intercellular, meaning "between cells" Early candidates include: Sema3A, Notch, CREST, and Dasm1. Sema3A may act as a dendritic chemoattractant that aids cortical pyramidal neurons in orienting their apical dendrites to the pial surface. Notch acts as a neurotrophic factor in aiding dendrite growth and branching, while CREST may play an important role in regulating calcium dependent growth signals. Neurotrophins are a family of proteins that induce the survival development and function of Neurons. Dasm1 (Dendrite arborization and synapse maturation 1) expression appears to be highly localized to dendrites and may have substantial influence on dendrite (but not axon) development.
See also
References
- Kandel ER, Schwartz JH, Jessell TM. Neurons (ˈnjuːɹɒn also known as neurones and nerve cells) are responsive cells in the Nervous system that process and transmit information A dendritic spine (or spine is a small membranous protrusion from a neuron's Dendrite that typically receives input from a single Synapse An axon or nerve fiber is a long slender projectionof a nerve cell or Neuron, that conducts electrical impulses away from the neuron's Cell Chemical synapses are specialized junctions through which Neurons signal to each other and to non-neuronal cells such as those in Muscles or Glands For the cells of the Electrical conduction system of the heart, see Purkinje fibers Purkinje cells (or Purkinje neurons) are a class of A pyramidal cell (or pyramidal neuron, or projection neuron) is a multipolar Neuron located in the Hippocampus and Cerebral Eric Richard Kandel (born November 7, 1929) is a Psychiatrist, a neuroscientist and Professor of Biochemistry Principles of Neural Science, 4th ed. First published in 1981 by Elsevier, Principles of Neural Science is a Neuroscience Textbook edited by Eric R McGraw-Hill, New York (2000). ISBN 0-8385-7701-6
- Koch C. Christof Koch (born November 13, 1956, Kansas City) is an American neuroscientist working on the neural basis of Consciousness Biophysics of Computation, Oxford University Press, Oxford (1999). ISBN 0-19-510491-9
- Stuart G, Spruston N, Hausser M. Dendrites, Oxford University Press, USA (2008). ISBN 0-1985-6656-5
External links
- Histology at OU 3_09 - "Slide 3 Spinal cord"
Dictionary
dendrite
-noun
- (cytology) A slender projection of a nerve cell which conducts nerve impulses from a synapse to the body of the cell; a dendron.
- (cytology) Slender cell process emanating from the cell bodies of dendritic cells and follicular dendritic cells of the immune system.
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