Dendrite

Information about Dendrite

For the dendritic crystal structure, see .

Dendrite
Dendrite Soma Axon Nucleus Node of Ranvier Axon Terminal Schwann cell Myelin sheath
Structure of a typical neuron

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. Electrical stimulation is transmitted onto dendrites by upstream neurons via synapses which are located at various points throughout the dendritic arbor. Dendrites play a critical role in integrating these synaptic inputs and in determining the extent to which action potentials are produced by the neuron.

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. 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. 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. 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. Sodium, calcium, and potassium channels are all implicated in contributing to input modulation. 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. Such characteristics include the latency of channel opening, the electrical conductance of the ion pore, the activation voltage, and the activation duration. 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. 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. It is likely that a complex array of extracellular and intracellular cues modulate dendrite development. 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. 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.

References

Kandel ER, Schwartz JH, Jessell TM. Principles of Neural Science, 4th ed. McGraw-Hill, New York (2000). ISBN 0-8385-7701-6
Koch C. 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"

• • [ e] Histology: nervous tissue
Neurons (gray matter)	soma, axon (axon hillock, axoplasm, axolemma, neurofibril/neurofilament), dendrite (Nissl body, dendritic spine) types (bipolar, pseudounipolar, multipolar, pyramidal, Purkinje, granule)
Afferent nerve/Sensory nerve/Sensory neuron	GSA, GVA, SSA, SVA, fibers Ia, Ib or Golgi, II or Aβ, III or Aδ or fast pain, IV or C or slow pain
Efferent nerve/Motor nerve/Motor neuron	GSE, GVE, SVE, Upper motor neuron, Lower motor neuron (Aα motorneuron, Aγ motorneuron)
Synapses	neuropil, synaptic vesicle, neuromuscular junction, electrical synapse - Interneuron (Renshaw)
Sensory receptors	Free nerve ending, Meissner's corpuscle, Merkel nerve ending, Muscle spindle, Pacinian corpuscle, Ruffini ending, Olfactory receptor neuron, Photoreceptor cell, Hair cell, Taste bud
Glial cells	astrocyte, oligodendrocyte, ependymal cells, microglia, radial glia
Myelination (white matter)	Schwann cell, oligodendrocyte, nodes of Ranvier, internode, Schmidt-Lanterman incisures, neurolemma
Related connective tissues	epineurium, perineurium, endoneurium, nerve fascicle, meninges

The soma, or perikaryon, is the bulbous end of a neuron, containing the cell nucleus. It is also known as the cell body. The word soma is Greek, meaning "body"; the soma of a neuron is often called the "cell body".
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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.

Anatomy

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nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (ER) (6) Golgi apparatus (7) Cytoskeleton (8) smooth ER (9) mitochondria (10) vacuole (11) cytoplasm (12) lysosome (13) centrioles]]

In cell biology, the nucleus (pl.
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Nodes of Ranvier, also known as neurofibril nodes, are regularly spaced gaps in the myelin sheath around an axon or nerve fiber. About one micrometer in length, these gaps expose the axonal membrane to the extracellular fluid.
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synapse. Synapses allow nerve cells to communicate with one another through axons and dendrites, converting electrical impulses into chemical signals.]]

Chemical synapses
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Named after the German physiologist Theodor Schwann, Schwann cells (also referred to as neurolemmocytes) are a variety of glial cell that mainly provide myelin insulation to axons in the peripheral nervous system of jawed vertebrates.
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Myelin is an electrically insulating phospholipid layer that surrounds the axons of many neurons. It is an outgrowth of glial cells: Schwann cells supply the myelin for peripheral neurons while oligodendrocytes supply it to those of the central nervous system.
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Greek}}}
Writing system: Greek alphabet
Official status
Official language of: Greece
Cyprus
European Union
recognised as minority language in parts of:
European Union
Italy
Turkey
Regulated by:
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Neurons (also known as neurones and nerve cells) are electrically excitable cells in the nervous system that process and transmit information. In vertebrate animals, neurons are the core components of the brain, spinal cord and peripheral nerves.
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An action potential is a "spike" of electrical discharge that travels along the membrane of a cell. Action potentials are an essential feature of animal life, rapidly carrying information within and between tissues. They also occur in some plants.
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Voltage-gated ion channels are a class of transmembrane ion channels that are activated by changes in electrical potential difference near the channel; these types of ion channels are especially critical in neurons, but are common in many types of cells.
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Voltage (sometimes also called electric potential difference or electrical tension) is the potential similarity of electrical potential between two points of an electrical or electronic circuit, expressed in volts.
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cable theory describes the development of mathematical models that can calculate the flow of electric current (and accompanying voltage) along passive ^[1]
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Proteins are large organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues.
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Sodium (IPA: /ˈsəʊdiəm/) is a chemical element which has the symbol Na (Latin: natrium), atomic number 11, atomic mass 22.9898 g/mol, common oxidation number +1.
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Calcium (IPA: /ˈkalsiəm/) is the chemical element in the periodic table that has the symbol Ca and atomic number 20. It has an atomic mass of 40.078.
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Potassium (IPA: /pə(ʊ)ˈtasiəm/, /pə'tæsiəm/) is a chemical element. It has the symbol K (Arabic: al qalja
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ion is an atom or molecule which has lost or gained one or more electrons, making it positively or negatively charged. A negatively charged ion, which has more electrons in its electron shells than it has protons in its nuclei, is known as an anion
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Latency is a time delay between the moment something is initiated, and the moment one of its effects begins or becomes detectable. The word derives from the fact that during the period of latency the effects of an action are latent, meaning "potential" or "not yet observed".
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Electrical conductance is the reciprocal of electrical resistance. It is a measure of how easily electricity flows along a certain path through an electrical element. The SI derived unit of conductance is the siemens (formerly referred to as the reciprocal ohm or mho).
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long-term potentiation (LTP) is the long-lasting improvement in communication between two neurons that results from stimulating them simultaneously.^[1] Since neurons communicate via chemical synapses, and because memories are believed to be stored within these
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In vivo (Latin: (with)in the living) means that which takes place inside an organism. In science, in vivo refers to experimentation done in or on the living tissue of a whole, living organism as opposed to a partial or dead one.
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In cell biology, molecular biology and related fields, the word extracellular (or sometimes extracellular space) means "outside the cell". This space is usually taken to be outside the plasma membranes, and occupied by fluid.
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In cell biology, molecular biology and related fields, the word intracellular means "inside the cell".

It is used in contrast to extracellular (outside the cell). The cell membrane (and, in plants, the cell wall) is the barrier between the two, and chemical composition of
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Neurotrophins, also called "neurotrophic factors", are a family of protein which induce the survival of neurons. They belong to a family of growth factors, secreted proteins usually found in the blood stream which are capable of signaling particular cells to survive, differentiate,
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