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Encyclopedia > Axon
Structure of a typical neuron
Neuron

An axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma. Image File history File links Neuron-no_labels. ... 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 perikaryon, is the bulbous end of a neuron, containing the cell nucleus. ... HeLa cells stained for DNA with the Blue Hoechst dye. ... Nodes of Ranvier are regularly spaced gaps in the myelin sheath around an axon or nerve fiber. ... Nodes of Ranvier are regularly spaced gaps in the myelin sheath around an axon or nerve fiber. ... Illustration of the major elements in a prototypical synapse. ... Named after the German physiologist Theodor Schwann, Schwann cells are a variety of neuroglia that mainly provide myelin insulation to axons in the peripheral nervous system of jawed vertebrates. ... In neuroscience, myelin is an electrically insulating fatty layer that surrounds the axons of many neurons, especially those in the peripheral nervous system. ... This article is about cells in the nervous system. ... A. A schematic view of an idealized action potential illustrates its various phases as the action potential passes a point on a cell membrane. ... The cell body or soma is a structure in a neuron consisting of the main part of the cell and containing the nucleus. ...

Contents

Anatomy

Axons are in effect the primary transmission lines of the nervous system, and as bundles they help make up nerves. Individual axons are microscopic in diameter (typically about 1μm across), but may be up to multiple feet long. The longest axons in the human body, for example, are those of the sciatic nerve, which run from the base of the spine to the big toe of each foot. These single-cell fibers of the sciatic nerve may extend a meter or even longer. The nervous system is a highly specialized network whose principal components are cells called neurons. ... Nerves (yellow) Nerves redirects here. ... A micrometre (American spelling: micrometer, symbol µm) is an SI unit of length equal to one millionth of a metre, or about a tenth of the diameter of a droplet of mist or fog. ... The sciatic nerve (also known as the ischiatic nerve) is a large nerve that runs down the lower limb. ... The vertebral column seen from the side The vertebral column (backbone or spine) is a column of vertebrae situated in the dorsal aspect of the abdomen. ... The sciatic nerve (also known as the ischiatic nerve) is a large nerve that runs down the lower limb. ...


In vertebrates, the axons of many neurons are sheathed in myelin, which is formed by either of two types of glial cells: Schwann cells ensheathing peripheral neurons and oligodendrocytes insulating those of the central nervous system. Along myelinated nerve fibers, gaps in the sheath known as nodes of Ranvier occur at evenly-spaced intervals, enabling an especially rapid mode of electrical impulse propagation called saltation. The demyelination of axons is what causes the multitude of neurological symptoms found in the disease Multiple Sclerosis. The axons of some neurons branch to form axon collaterals, that can be divided into a number of smaller branches called telodendria. Along these the bifurcated impulse travels simultaneously to signal more than one other cell. This article does not cite any references or sources. ... Myelin is an electrically insulating phospholipid layer that surrounds the axons of many neurons. ... Neuroglia cells of the brain shown by Golgis method. ... Named after the German physiologist Theodor Schwann, Schwann cells are a variety of neuroglia that mainly provide myelin insulation to axons in the peripheral nervous system of jawed vertebrates. ... The peripheral nervous system or PNS, is part of the nervous system, and consists of the nerves and neurons that reside or extend outside the central nervous system--to serve the limbs and organs, for example. ... Oligodendrocytes (from Greek literally meaning few tree cells), or oligodendroglia (Greek, few tree glue),[1] are a variety of neuroglia. ... A diagram showing the CNS: 1. ... This article is about anatomy; for the musical group see Nodes of Ranvier (band) Nodes of Ranvier are regularly spaced gaps in the myelin sheath around an axon or nerve fiber. ... Saltatory conduction (from the Latin saltare, to hop or leap) is a means by which action potentials are transmitted along myelinated nerve fibers. ... Multiple sclerosis (abbreviated MS, formerly known as disseminated sclerosis or encephalomyelitis disseminata) is a chronic, inflammatory, demyelinating disease that affects the central nervous system (CNS). ...


Physiology

The physiology can be described by the Hodgkin-Huxley Model, extended to vertebrates in Frankenhaeuser-Huxley equations. This article or section does not cite any references or sources. ... The Hodgkin-Huxley Model is a set of non-linear ordinary differential equations, named after Alan Lloyd Hodgkin and Andrew Huxley, that approximates the electrical characteristics of excitable cells such as neurons and cardiac myocytes. ...


Types

Peripheral nerve fibers can be classified based on axonal conduction velocity, mylenation, fiber size etc. For example, there are slow-conducting unmyelinated C fibers and faster-conducting myelinated Aδ fibers. More complex mathematical modeling continues to be done today. C-fibers are unmyeliniated and as a result, have a slower conduction velocity, lower than 2 m/s. ... Aδ fibres are thin, myelinated fibers with a fast conduction velocity, or speed of travel of a nerve signal (2 to 30 m/s) and are associated with acute pain, the sharp pain that triggers reflexes which result in the pulling away from the stimuli (ie: yanking hand away from...


There are several types of sensory- as well as motorfibers. Other fibers not mentioned in table are e.g. fibers of the autonomic nervous system This article or section is in need of attention from an expert on the subject. ...


Motor

Lower motor neurons have two kind of fibers: Lower motor neurons (LMNs) are the motoneurons connecting the brainstem and spinal cord to muscle fibers, bringing the nerve impulses from the upper motor neurons out to the muscles. ...

Motor fiber types
Type Diameter Conduction velocity Associated muscle fibers
α Extrafusal muscle fibers
γ 4-24 m/s[1][2] Intrafusal muscle fibers

A simplified, global view of a neuromuscular junction: 1. ... Extrafusal muscle fibers are a class of muscle fiber innervated by alpha motor neurons. ... Intrafusal muscle fibers are muscle fibers that comprise the muscle spindle. ...

Sensory

Different sensory receptors are innervated by different types of nerve fibers. Muscles and associated sensory receptors are innvervated by type I and II sensory fibers, while cutaneous receptors are innervated by Aβ, Aδ and C fibers. In a sensory system, a sensory receptor is a structure that recognizes a stimulus in the internal or external environment of an organism. ...

Sensory fiber types
Type Diameter Conduction velocity Associated sensory receptors
Ia & II Receptors of muscle spindle
Ib Golgi tendon organ
6-12 µm diameter 33-75 m/s All cutaneous mechanoreceptors
1-5 µm 3-30 m/s Free nerve endings of touch and pressure
Cold thermoreceptors
Nociceptors of neospinothalamic tract
C 0.2-1.5 µm 0.5-2.0 m/s Nociceptors of paleospinothalamic tract
warmth receptors

In a sensory system, a sensory receptor is a structure that recognizes a stimulus in the internal or external environment of an organism. ... Type Ia Sensory Fiber also called Primary Afferent Type 1A Fiber or Group II sensory fibers is a component of a muscle fibers muscle spindle which keeps track of the how fast a muscle stretch changes (the velocity of the stretch). ... A muscle spindle is a specialized muscle structure innervated by both sensory and motor neuron axons. ... Organ of Golgi (neurotendinous spindle) from the human tendo calcaneus. ... A micrometre (American spelling: micrometer, symbol µm) is an SI unit of length. ... Aδ fibres are thin, myelinated fibers with a fast conduction velocity, or speed of travel of a nerve signal (2 to 30 m/s) and are associated with acute pain, the sharp pain that triggers reflexes which result in the pulling away from the stimuli (ie: yanking hand away from... A micrometre (American spelling: micrometer, symbol µm) is an SI unit of length. ... NERVE ENDINGS SUCK PENIS!!! ... A thermoreceptor is a sensory receptor that responds to temperature, primarily within the innocuous range. ... A nociceptor is a sensory receptor that responds only after a high level of stimuli or a level enough to hurt the individual. ... Pain redirects here. ... C-fibers are part of the human sensory system, the part of the nervous system responsible for processing sensory information. ... A micrometre (American spelling: micrometer, symbol µm) is an SI unit of length. ... A nociceptor is a sensory receptor that responds only after a high level of stimuli or a level enough to hurt the individual. ...

Growth and development

Growing axons move through their environment via the growth cone, which is at the tip of the axon. The growth cone has a broad sheet like extension called lamellipodia which contain protrusions called filopodia. The filopodia are the mechanism by which the entire process adheres to surfaces and explores the surrounding environment. Actin plays a major role in the mobility of this system. Environments with high levels of cell adhesion molecules or CAM's create an ideal environment for axonal growth. This seems to provide a "sticky" surface for axons to grow along. Examples of CAM's specific to neural systems include N-CAM, neuroglial CAM or NgCAM, TAG-1, MAG, and DCC, all of which are part of the immunoglobulin superfamily. Another set of molecules called extracellular matrix adhesion molecules also provide a sticky substrate for axons to grow along. Examples of these molecules include laminin, fibronectin, tenascin, and perlecan. Some of these are surface bound to cells and thus act as short range attractants or repellents. Others are difusible ligands and thus can have long range effects. Image of a growth cone (red) extending from an axon (green). ... A GFP label of the actin cytoskeleton in a melanoma cell, showing a ruffled-edge lamellipodium, from Cell Biology at IMB Salzburg. ... Filopodia of macrophages. ... G-Actin (PDB code: 1j6z). ... Cell Adhesion Molecules (CAMs) are proteins located on the cell surface involved with the binding with other cells or with the extracellular matrix (ECM) in the process called cell adhesion. ... Neural Cell Adhesion Molecule (NCAM, also the cluster of differentiation CD56) is a homophilic binding glycoprotein expressed on the surface of neurons, glia and skeletal muscle. ... Dicyclohexylcarbodiimide (DCC) is an organic compound with chemical formula C13H22N2 whose primary use is to couple amino acids during artificial protein synthesis. ... Schematic of antibody binding to an antigen An antibody is a protein complex used by the immune system to identify and neutralize foreign objects like bacteria and viruses. ... Laminins are the major non-collagenous component of the basal lamina, such as those on which cells of an epithelium sit. ... Fibronectin is a high-molecular-weight glycoprotein containing about 5% carbohydrate that binds to receptor proteins that span the cells membrane, called integrins. ... Tenascins are extracellular matrix glycoproteins. ... Perlecan is a large multidomain proteoglycan that binds to and cross-links many extracellualr matrix (ECM) components and cell-surface molecules. ...


Cells called guidepost cells assist in the guidance of neuronal axon growth. These cells are typically other, sometimes immature, neurons.


History

Some of the first intracellular recordings in a nervous system were made in the late 1930's by K. Cole and H. Curtis. 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 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. Erlanger and Gasser later developed the classification system for peripheral nerve fibers, based on axonal conduction velocity, mylenation, fiber size etc. Even recently our understanding of the biochemical basis for action potential propagation has advanced, and now includes many details about individual ion channels. Sir Alan Lloyd Hodgkin (February 5, 1914 _ December 20, 1998) was a British physiologist and biophysicist, who won the 1963 Nobel Prize in Physiology or Medicine for his work with Andrew Fielding Huxley on the basis of nerve action potentials, the electrical impulses that enable the activity of an... Andrew Huxley at Trinity College, Cambridge, July 2005 Family tree Sir Andrew Fielding Huxley, OM, FRS (born 22 November 1917, Hampstead, London) is an English physiologist and biophysicist, who won the 1963 Nobel Prize in Physiology or Medicine for his work with Alan Lloyd Hodgkin on the basis of nerve... The squid giant axon is the very large (up to 1 mm in diameter; typically around 0. ... A. A schematic view of an idealized action potential illustrates its various phases as the action potential passes a point on a cell membrane. ... The Hodgkin-Huxley Model is a set of non-linear ordinary differential equations, named after Alan Lloyd Hodgkin and Andrew Huxley, that approximates the electrical characteristics of excitable cells such as neurons and cardiac myocytes. ... Emil Adolf von Behring was the first person to receive the Nobel Prize in Physiology or Medicine, for his work on the treatment of diphtheria. ... For other uses, see 1963 (disambiguation). ... Ion channels are pore-forming proteins that help to establish and control the small voltage gradient that exists across the plasma membrane of all living cells (see cell potential) by allowing the flow of ions down their electrochemical gradient. ...


Concussion

Concussion is considered a mild form of diffuse axonal injury [3].


See also

This article is about cells in the nervous system. ... 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. ... Illustration of the major elements in a prototypical synapse. ... This article or section does not cite any references or sources. ... Current Clamp is a common technique in electrophysiology. ...

References

  1. ^ Andrew BL, Part NJ (1972) Properties of fast and slow motor units in hind limb and tail muscles of the rat. Q J Exp Physiol Cogn Med Sci 57:213-225.
  2. ^ Russell NJ (1980) Axonal conduction velocity changes following muscle tenotomy or deafferentation during development in the rat. J Physiol 298:347-360.
  3. ^ eMedicine - Traumatic Brain Injury: Definition, Epidemiology, Pathophysiology : Article by Segun T Dawodu, MD, FAAPMR, FAANEM, CIME, DipMI(RCSed)

Image File history File links Question_book-3. ...

External links

University of Oklahoma, abbreviated OU, is a coeducational public research university located in the U.S. state of Oklahoma. ... The Spinal cord nested in the vertebral column. ... A thin section of lung tissue stained with hematoxylin and eosin. ... Nervous tissue is the fourth major class of vertebrate tissue. ... This article is about cells in the nervous system. ... Grey matter (or gray matter) is a major component of the central nervous system, consisting of nerve cell bodies, glial cells (astroglia and oligodendrocytes), capillaries, and short nerve cell extensions/processes (axons and dendrites). ... The soma, or perikaryon, is the bulbous end of a neuron, containing the cell nucleus. ... The arrow labeled axon is pointing directly at the axon hillock. ... Axoplasm is the cytoplasm of the axon of a neuron. ... The axolemma is the membrane of a neurons axon. ... Intermediate filaments are one component of the cytoskeleton - important structural components of living cells. ... 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. ... Image of a Nissl-stained histological section through the rodent hippocampus showing various classes of neurons. ... Close up of the dendrite of a striatal medium spiny neuron. ... An apical dendrite is a dendrite that emerges from the apex of a pyramidal cell. ... A basal dendrite is a dendrite that emerges from the base of a pyramidal cell. ... As a part of the retina, the bipolar cell exists between photoreceptors (rod cells and cone cells) and ganglion cells. ... Pseudounipolar cells (Pseudo- false, uni- one) are sensory neurons in the peripheral nervous system. ... The multipolar neuron possesses a single (usually long) axon and many dendrites, allowing for the integration of a great deal of information from other neurons. ... A pyramidal cell (or pyramidal neuron, or projection neuron) is a multipolar neuron located in the hippocampus and cerebral cortex. ... Drawing of pigeon Purkinje cells (A) by Santiago Ramon y Cajal Purkinje cells are a class of GABAergic neuron located in the cerebellar cortex. ... In neuroscience, granule cells are tiny cells found within the granular layer of the cerebellum. ... The mechanism of the reflex arc In the nervous system, afferent neurons--otherwise known as sensory or receptor neurons--carry nerve impulses from receptors or sense organs toward the central nervous system. ... The mechanism of the reflex arc Sensory neurons (or neurones) are nerve cells within the nervous system responsible for converting external stimuli from the organisms environment into internal electrical impulses. ... The mechanism of the reflex arc Sensory neurons (neurones) are nerve cells within the nervous system responsible for converting external stimuli from the organisms environment into internal electrical motor reflex loops and several forms of involuntary behavior, including pain avoidance. ... The general somatic afferent fibers (or somatic sensory fibers), afferent fibers, arise from cells in the spinal ganglia and are found in all the spinal nerves, except occasionally the first cervical, and conduct impulses of pain, touch and temperature from the surface of the body through the posterior roots to... The general visceral afferent fibers (GVA, or sympathetic afferent fibers), conduct sensory impulses from the viscera through the rami communicantes and posterior roots to the spinal cord. ... Special somatic afferent (SSA) refers to efferent nerves which supply muscles derived from ectoderm. ... Special visceral afferent (SVA) refers to afferent nerves supporting the gastrointestinal tract. ... An axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ... Type Ia Sensory Fiber also called Primary Afferent Type 1A Fiber or Group II sensory fibers is a component of a muscle fibers muscle spindle which keeps track of the how fast a muscle stretch changes (the velocity of the stretch). ... Organ of Golgi (neurotendinous spindle) from the human tendo calcaneus. ... Type II sensory fiber are the second of the two main groups of stretch receptors. ... A delta fibers (Aδ) are the fibers which convey fast pain information. ... C-fibers are unmyeliniated and as a result, have a slower conduction velocity, lower than 2 m/s. ... In the nervous system, efferent nerves otherwise known as motor or effector neuron carry nerve impulses away from the central nervous systemto effectors - either muscles or glands. ... Motor nerves allow the brain to stimulate muscle contraction. ... In vertebrates, the term motor neuron (or motoneuron) classically applies to neurons located in the central nervous system (CNS) which project their axons outside the CNS and directly or indirectly control muscles. ... The general somatic efferent fibers (or somatic motor fibers), efferent fibers, arise from cells in the anterior column of the spinal cord and pass out through the anterior roots to the voluntary muscles. ... The general visceral efferent fibers (GVE or sympathetic efferent fibers), probably arise from cells in the lateral column or the base of the anterior column and emerge through the anterior roots and white rami communicantes. ... Special visceral efferent (SVE) refers to efferent nerves which supply muscles which derived from the branchial arches. ... Upper motor neurons are any neurons that carry motor information down to the final common pathway, that is, any neurons that are not directly responsible for stimulating the target muscle. ... Lower motor neurons (LMNs) are the motoneurons connecting the brainstem and spinal cord to muscle fibers, bringing the nerve impulses from the upper motor neurons out to the muscles. ... Alpha motor neurons (α-MNs) are large lower motor neurons of the brainstem and spinal cord. ... A muscle spindle, with γ motor and Ia sensory fibers Gamma motoneurons (γ-motoneurons), also called gamma motor neurons, are a component of the fusimotor system, the system by which the central nervous system controls muscle spindle sensitivity. ... Illustration of the major elements in a prototypical synapse. ... Neuropil is the feltwork of unmyelinated neuronal processes (axonal and dendritic) within the gray matter of the central nervous system Traditionally, when pathologists looked at brain tissue they concentrated on neurons (the active functioning cells of the brain), glial cells and axons (especially in white matter, which is mostly composed... In a neuron, synaptic vesicles, also called neurotransmitter vesicles, store the various neurotransmitters that are released during calcium-regulated exocytosis at the presynaptic terminal into the synaptic cleft of a synapse. ... A neuromuscular junction is the junction of the axon terminal of a motoneuron with the motor end plate, the highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potentials across the muscles surface. ... An electrical synapse is a mechanical and electrically conductive link between two abutting neurons that is formed at a narrow gap between the pre- and postsynaptic cells known as a gap junction. ... An interneuron (also called relay neuron,association neuron or bipolar neuron) is a term used to describe a neuron which has two different common meanings. ... Renshaw cells are located in the spinal cord horn. ... In a sensory system, a sensory receptor is a structure that recognizes a stimulus in the internal or external environment of an organism. ... NERVE ENDINGS SUCK PENIS!!! ... Meissners corpuscles (discovered by the anatomist Georg Meissner (1829-1903) are a type of mechanoreceptor and more specifically, a tactile corpuscle(corpusculum tactus). ... Merkel nerve endings are mechanoreceptors found in the skin and mucosa of vertebrates that provide touch information to the brain. ... A muscle spindle is a specialized muscle structure innervated by both sensory and motor neuron axons. ... A Pacinian corpuscle is a structure that functions as a mechanoreceptor. ... Ruffini Endings are one of the four main cutaneous mechanoreceptors. ... Bold text == Headline text == minni hi. ... This article is about cellular photoreceptors. ... Hair cells are the sensory cells of both the auditory system and the vestibular system in all vertebrates. ... Taste buds are small structures on the upper surface of the tongue, soft palate, and epiglottis that provide information about the taste of food being eaten. ... Neuroglia of the brain shown by Golgis method. ... Astrocytes (also known collectively as astroglia) are characteristic star-shaped glial cells in the brain. ... Oligodendrocytes (from Greek literally meaning few tree cells), or oligodendroglia (Greek, few tree glue),[1] are a variety of neuroglia. ... Ependyma is the thin epithelial membrane lining the ventricular system of the brain and the spinal cord canal. ... Microglia cells positive for lectins Microglia are a type of glial cell that act as the immune cells of the Central nervous system (CNS). ... Radial glial cells are a pivotal cell type in the developing CNS involved in key developmental processes, ranging from patterning and neuronal migration to their newly described role as precursors during neurogenesis. ... Myelin is an electrically insulating phospholipid layer that surrounds the axons of many neurons. ... White matter is one of the two main solid components of the central nervous system. ... Named after the German physiologist Theodor Schwann, Schwann cells are a variety of neuroglia that mainly provide myelin insulation to axons in the peripheral nervous system of jawed vertebrates. ... Oligodendrocytes (from Greek literally meaning few tree cells), or oligodendroglia (Greek, few tree glue),[1] are a variety of neuroglia. ... This article is about anatomy; for the musical group see Nodes of Ranvier (band) Nodes of Ranvier are regularly spaced gaps in the myelin sheath around an axon or nerve fiber. ... The portion of nerve fiber between two Nodes of Ranvier is called an internodal segment (or internode). ... Oblique clefts may be seen in the medullary sheath, subdividing it into irregular portions, which are termed Schmidt-Lanterman incisures (or clefts of schmidt-lanterman, segments of Lantermann, medullary segments. ... Neurolemma (spelled also neurolema, neurilemma and neurilema, and used interchangeably with epineurium) is the insulating myelin layer that surrounds an individual peripheral nerve fiber. ... Connective tissue is one of the four types of tissue in traditional classifications (the others being epithelial, muscle, and nervous tissue. ... Neurolemma (spelled also neurolema, neurilemma and neurilema, and used interchangeably with epineurium) is the insulating myelin layer that surrounds an individual peripheral nerve fiber. ... In a nerve fiber, the tubular sheath of the funiculi, perineurium, is a fine, smooth, transparent membrane, which may be easily separated, in the form of a tube, from the fibers it encloses; in structure it is made up of connective tissue, which has a distinctly lamellar arrangement. ... The nerve fibers are held together and supported within the funiculus by delicate connective tissue, called the endoneurium. ... A small bundle of fibers, enclosed in a tubular sheath, is called a funiculus; if the nerve is of small size, it may consist only of a single funiculus; but if large, the funiculi are collected together into larger bundles or nerve fascicles, which are bound together in a common... The meninges (singular meninx) are the system of membranes that envelop the central nervous system. ...

  Results from FactBites:
 
Axon - definition of Axon in Encyclopedia (287 words)
An axon, or "nerve fiber," is a long slender projection of a nerve cell, or "neuron," which conducts electrical impulses away from the neuron's cell body or soma.
The longest axons in the human body, for example, are those of the sciatic nerve, which run from the base of the spine to the big toe of each foot.
In vertebrates generally, the axons of many neurons are sheathed in myelin, which is formed by either of two types of glial cells: Schwann cells ensheathing peripheral neurons and oligodendrocytes insulating those of the central nervous system.
Axon - Wikipedia, the free encyclopedia (515 words)
An axon, or nerve fiber, is a long slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma.
In vertebrates, the axons of many neurons are sheathed in myelin, which is formed by either of two types of glial cells: Schwann cells ensheathing peripheral neurons and oligodendrocytes insulating those of the central nervous system.
Growing axons move through their environment via the growth cone, which is at the tip of the axon.
  More results at FactBites »

 
 

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