1.
Dendritic cell
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Dendritic cells are antigen-presenting cells of the mammalian immune system. Their main function is to process antigen material and present it on the surface to the T cells of the immune system. They act as messengers between the innate and the immune systems. Dendritic cells are present in tissues that are in contact with the external environment, such as the skin. They can also be found in a state in the blood. Once activated, they migrate to the nodes where they interact with T cells and B cells to initiate. At certain development stages they grow branched projections, the dendrites that give the cell its name, while similar in appearance, these are structures distinct from the dendrites of neurons. Immature dendritic cells are also called veiled cells, as they possess large cytoplasmic veils rather than dendrites, dendritic cells were first described by Paul Langerhans in the late nineteenth century. The term dendritic cells was coined in 1973 by Ralph M. Steinman, the morphology of dendritic cells results in a very large surface-to-volume ratio. That is, the cell has a very large surface area compared to the overall cell volume. The most common division of cells is myeloid vs. plasmacytoid, The markers BDCA-2, BDCA-3. Lymphoid and myeloid DCs evolve from lymphoid and myeloid precursors, respectively, the blood DCs are typically identified and enumerated in flow cytometry. Three types of DCs have been defined in human blood, the CD1c+ myeloid DCs, the CD141+ myeloid DCs and this represents the nomenclature proposed by the nomenclature committee of the International Union of Immunological Societies. Dendritic cells that circulate in blood do not have all the features of their counterparts in tissue. Still, they can perform functions including chemokine-production, cross-presentation. In some respects, dendritic cells cultured in vitro do not show the behaviour or capability as dendritic cells isolated ex vivo. Nonetheless, they are used for research as they are still much more readily available than genuine DCs. Mo-DC or MDDC refers to cells matured from monocytes HP-DC refers to cells derived from hematopoietic progenitor cells, while humans and non-human primates such as rhesus macaques appear to have DCs divided into these groups, other species have different subdivisions of DCs
2.
Soma (biology)
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The soma, perikaryon, cyton, or cell body is the bulbous, non-process portion of a neuron or other brain cell type, containing the cell nucleus. The word soma comes from the Greek σῶμα, meaning body, although it is often used to refer to neurons, it can also refer to other cell types as well, including astrocytes, oligodendrocytes, and microglia. The soma of a neuron contains many organelles, including granules called Nissl granules, the cell nucleus is a key feature of the soma. The nucleus is the source of most of the RNA that is produced in neurons, in general, most proteins are produced from mRNAs that do not travel far from the cell nucleus. This creates a challenge for supplying new proteins to axon endings that can be a meter or more away from the soma, axons contain microtubule-associated motor proteins that transport protein-containing vesicles between the soma and the synapses at the axon terminals. Such transport of molecules towards and away from the soma maintains critical cell functions, the axon hillock is a specialized domain of the neuronal cell body from which the axon originates. A high amount of protein synthesis occurs in this region, as it contains a number of Nissl granules and polyribosomes. Within the axon hillock, materials are sorted as either items that will enter the axon or will remain in the soma. In addition, the axon hillock also has a plasma membrane that contains large numbers of voltage-gated ion channels. The survival of some sensory neurons depends on axon terminals making contact with sources of survival factors that prevent apoptosis, the survival factors are neurotrophic factors, including molecules such as nerve growth factor. NGF interacts with receptors at axon terminals, and this produces a signal that must be transported up the length of the axon to the nucleus, histology image, 3_09 at the University of Oklahoma Health Sciences Center - Slide 3 Spinal cord
3.
Axon
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An axon, is a long, slender projection of a nerve cell, or neuron, that typically conducts electrical impulses away from the neurons cell body. Axons are also known as nerve fibers, the function of the axon is to transmit information to different neurons, muscles and glands. Axon dysfunction has caused many inherited and acquired neurological disorders which can affect both the peripheral and central neurons, nerve fibers are classed into three types – A delta fibers, B fibers, and C fibres. A and B are myelinated and C are unmyelinated, an axon is one of two types of protoplasmic protrusions that extrude from the cell body of a neuron, the other type being dendrites. Axons are distinguished from dendrites by several features, including shape, length, all of these rules have exceptions, however. Axons are covered by a known as axolemma, the cytoplasm of axon is called axoplasm. Some types of neurons have no axon and transmit signals from their dendrites, no neuron ever has more than one axon, however in invertebrates such as insects or leeches the axon sometimes consists of several regions that function more or less independently of each other. Most axons branch, in cases very profusely. Axons make contact with other cells—usually other neurons but sometimes muscle or gland cells—at junctions called synapses, at a synapse, the membrane of the axon closely adjoins the membrane of the target cell, and special molecular structures serve to transmit electrical or electrochemical signals across the gap. Some synaptic junctions appear partway along an axon as it extends—these are called en passant synapses, other synapses appear as terminals at the ends of axonal branches. A single axon, with all its branches together, can innervate multiple parts of the brain. Axons are the transmission lines of the nervous system. Some axons can extend up to one meter or more while others extend as little as one millimeter, the longest axons in the human body are those of the sciatic nerve, which run from the base of the spinal cord to the big toe of each foot. The diameter of axons is also variable, most individual axons are microscopic in diameter. The largest mammalian axons can reach a diameter of up to 20 µm, the squid giant axon, which is specialized to conduct signals very rapidly, is close to 1 millimetre in diameter, the size of a small pencil lead. Axonal arborization also differs from one nerve fiber to the next, axons in the central nervous system typically show complex trees with many branch points. In comparison, the granule cell axon is characterized by a single T-shaped branch node from which two parallel fibers extend. Elaborate arborization allows for the transmission of messages to a large number of target neurons within a single region of the brain
4.
Cell nucleus
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In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. Eukaryotes usually have a nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei. Cell nuclei contain most of the genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones. The genes within these chromosomes are the nuclear genome and are structured in such a way to promote cell function. The nucleus maintains the integrity of genes and controls the activities of the cell by regulating gene expression—the nucleus is, therefore, because the nuclear membrane is impermeable to large molecules, nuclear pores are required to regulate nuclear transport of molecules across the envelope. The pores cross both nuclear membranes, providing a channel through which larger molecules must be transported by carrier proteins while allowing free movement of small molecules. Movement of large molecules such as proteins and RNA through the pores is required for gene expression and the maintenance of chromosomes. The best-known of these is the nucleolus, which is involved in the assembly of ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA, the nucleus was the first organelle to be discovered. What is most likely the oldest preserved drawing dates back to the early microscopist Antonie van Leeuwenhoek and he observed a lumen, the nucleus, in the red blood cells of salmon. Unlike mammalian red blood cells, those of other vertebrates still contain nuclei, the nucleus was also described by Franz Bauer in 1804 and in more detail in 1831 by Scottish botanist Robert Brown in a talk at the Linnean Society of London. Brown was studying orchids under microscope when he observed an opaque area and he did not suggest a potential function. In 1838, Matthias Schleiden proposed that the plays a role in generating cells. He believed that he had observed new cells assembling around cytoblasts, Franz Meyen was a strong opponent of this view, having already described cells multiplying by division and believing that many cells would have no nuclei. The function of the nucleus remained unclear, between 1877 and 1878, Oscar Hertwig published several studies on the fertilization of sea urchin eggs, showing that the nucleus of the sperm enters the oocyte and fuses with its nucleus. This was the first time it was suggested that an individual develops from a nucleated cell, therefore, the necessity of the sperm nucleus for fertilization was discussed for quite some time. However, Hertwig confirmed his observation in other groups, including amphibians. Eduard Strasburger produced the results for plants in 1884
5.
Node of Ranvier
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Nodes of Ranvier, also known as myelin sheath gaps, are periodic gaps in the insulating myelin sheaths of myelinated axons where the axonal membrane is exposed to the extracellular space. Nodes of Ranvier are uninsulated and highly enriched in ion channels, nerve conduction in myelinated axons is referred to as saltatory conduction because of the manner in which the action potential seems to jump from one node to the next along the length of the axon. This results in conduction of the action potential. Many vertebrate axons are surrounded by a sheath, allowing rapid. The contacts between neurons and glial cells display a high level of spatial and temporal organization in myelinated fibers. The internodal glial membranes are fused to form compact myelin, whereas the cytoplasm-filled paranodal loops of myelinating cells are spirally wrapped around the axon at both sides of the nodes. This organization demands a tight control and the formation of a variety of specialized zones of contact between different areas of the myelinating cell membrane. Each node of Ranvier is flanked by paranodal regions where helicoidally wrapped glial loops are attached to the membrane by a septate-like junction. The segment between nodes of Ranvier is termed as the internode, and its outermost part that is in contact with paranodes is referred to as the juxtaparanodal region. The nodes are encapsulated by microvilli stemming from the aspect of the Schwann cell membrane in the PNS. The myelin sheath of nerves was discovered and named by German pathological anatomist Rudolf Virchow in 1854. French pathologist and anatomist Louis-Antoine Ranvier later discovered the nodes, or gaps, born in Lyon, Ranvier was one of the most prominent histologists of the late 19th century. Ranvier abandoned pathological studies in 1867 and became an assistant of physiologist Claude Bernard and he was the chairman of General Anatomy at the Collège de France in 1875. His refined histological techniques and his work on both injured and normal nerve fibers became world-renowned and his observations on fiber nodes and the degeneration and regeneration of cut fibers had a great influence on Parisian neurology at the Salpêtrière. Soon afterwards, he discovered gaps in sheaths of nerve fibers and this discovery later led Ranvier to careful histological examination of myelin sheaths and Schwann cells. The internodes are the segments and the gaps between are referred to as nodes. The size and the spacing of the internodes vary with the diameter in a curvilinear relationship that is optimized for maximal conduction velocity. The size of the span from 1–2 µm whereas the internodes can be up to 1.5 millimetres long, depending on the axon diameter and fiber type
6.
Axon terminal
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Axon terminals are distal terminations of the branches of an axon. The axon terminal, and the neuron from which it comes, is referred to as the presynaptic neuron. Neurotransmitters are packaged into vesicles that cluster beneath the axon terminal membrane on the presynaptic side of a synapse. The axonal terminals are specialized to release the neurotransmitters of the presynaptic cell, the terminals release transmitter substances into a gap called the synaptic cleft between the terminals and the dendrites of the next neuron. The information is received by the receptors of the postsynaptic cell that are connected to it. Neurons dont touch each other, but communicate across the synapse, the neurotransmitter molecule packages are created within the neuron, then travel down the axon to the distal axon terminal where they sit docked. Calcium ions then trigger a cascade which results in vesicles fusing with the presynaptic membrane. Triggered by the binding of the ions, the synaptic vesicle proteins begin to move apart. The presence of the pore allows for the release of neurotransmitter into the synaptic cleft, the process occurring at the axon terminal is exocytosis, which a cell uses to exude secretory vesicles out of the cell membrane. Exocytosis in neuronal chemical synapses is Ca2+ triggered and serves interneuronal signalling, dr. Wade Regehr, a Professor of Neurobiology at Harvard Medical Schools Department of Neurobiology, developed a method to physiologically see the synaptic activity that occurs in the brain. A dye alters the properties when attached to calcium. Using fluorescence-microscopy techniques calcium levels are detected, and therefore the influx of calcium in the presynaptic neuron, regehrs laboratory specializes in pre-synaptic calcium dynamics which occurs at the axon terminals. Regehr studies the implication of calcium Ca2+ as it affects synaptic strength, differential Autoreceptor Control of Somatodendritic and Axon Terminal Dopamine Release in Substantia Nigra, Ventral Tegmental Area, and Striatum. Vaquero, Cecilia F, de la Villa, Pedro, localisation of the GABAC receptors at the axon terminal of the rod bipolar cells of the mouse retina. OGorman, Stephen, Sidman, Richard L. Neurochemical and morphological consequences of axon terminal degeneration in cerebellar deep nuclei of mice with inherited purkinje cell degeneration. The axon terminal of goldfish retinal horizontal cells, A low membrane conductance measured in solitary preparations and its implication to the signal conduction from the soma
7.
Schwann cell
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Schwann cells or neurolemmocytes are the principal glia of the peripheral nervous system. There are two types of Schwann cell, myelinating and nonmyelinating, myelinating Schwann cells wrap around axons of motor and sensory neurons to form the myelin sheath. The Schwann cell promoter is present in the region of the human dystrophin gene that gives shortened transcript that are again synthesized in a tissue specific manner. Charcot–Marie–Tooth disease, Guillain–Barré syndrome, schwannomatosis, and chronic inflammatory demyelinating polyneuropathy, Schwann cells are a variety of glial cell that keep peripheral nerve fibres alive. In myelinated axons, Schwann cells form the myelin sheath, individual myelinating Schwann cells cover about 100 micrometres of an axon—equating to approximately 10,000 Schwann cells along a 1-metre length of the axon. The gaps between adjacent Schwann cells are called nodes of Ranvier, 9-O-acetyl GD3 ganglioside is an acetylated glycolipid which is found in the cell membranes of many types of vertebrate cells. During peripheral nerve regeneration, 9-O-acetyl GD3 is expressed by Schwann cells, the vertebrate nervous system relies on the myelin sheath for insulation and as a method of decreasing membrane capacitance in the axon. The action potential jumps from node to node, in a process called saltatory conduction, in this sense, Schwann cells are the peripheral nervous systems analogues of the central nervous systems oligodendrocytes. However, unlike oligodendrocytes, each myelinating Schwann cell provides insulation to only one axon and this arrangement permits saltatory conduction of action potentials with repropagation at the nodes of Ranvier. In this way, myelination greatly increases speed of conduction and saves energy, non-myelinating Schwann cells are involved in maintenance of axons and are crucial for neuronal survival. Some group around smaller axons and form Remak bundles, myelinating Schwann cells begin to form the myelin sheath in mammals during fetal development and work by spiraling around the axon, sometimes with as many as 100 revolutions. A well-developed Schwann cell is shaped like a sheet of paper. The inner layers of the wrapping, which are predominantly membrane material, only a small volume of residual cytoplasm allows communication between the inner and outer layers. This is seen histologically as the Schmidt-Lantermann incisure, Schwann cells are known for their roles in supporting nerve regeneration. Nerves in the PNS consist of axons myelinated by Schwann cells. If damage occurs to a nerve, the Schwann cells will aid in digestion of its axons, following this process, the Schwann cells can guide regeneration by forming a type of tunnel that leads toward the target neurons. The stump of the axon is able to sprout. The rate of regeneration decreases with time, because of their ability to impact regeneration of axons, Schwann cells have been connected to preferential motor reinnervation as well
8.
Myelin
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Myelin is a fatty white substance that surrounds the axon of some nerve cells, forming an electrically insulating layer. It is essential for the functioning of the nervous system. It is an outgrowth of a type of glial cell, the production of the myelin sheath is called myelination or myelinogenesis. In humans, myelination begins early in the 3rd trimester, although little myelin exists in the brain at the time of birth, during infancy, myelination occurs quickly, leading to a childs fast development, including crawling and walking in the first year. Myelination continues through the adolescent stage of life, schwann cells supply the myelin for the peripheral nervous system, whereas oligodendrocytes, specifically of the interfascicular type, myelinate the axons of the central nervous system. Myelin was discovered in 1854 by Rudolf Virchow, Myelin is made by different cell types, and varies in chemical composition and configuration, but performs the same insulating function. Myelinated axons are white in appearance, hence the matter of the brain. Myelin helps to insulate the axons from electrically charged atoms and molecules and these charged particles are found in the fluid surrounding the entire nervous system. Under a microscope, myelin looks like strings of sausages, cholesterol is an essential constituent of myelin. Myelin is about 40% water, the dry mass is about 70–85% lipids, some of the proteins are myelin basic protein, myelin oligodendrocyte glycoprotein, and proteolipid protein. The primary lipid of myelin is a glycolipid called galactocerebroside, the intertwining hydrocarbon chains of sphingomyelin serve to strengthen the myelin sheath. In brain, the myelin sheath covers the fibers of corpus callosum which constitute the part of cerebral hemisphere. The main purpose of a layer is to increase the speed at which impulses propagate along the myelinated fiber. Along unmyelinated fibers, impulses move continuously as waves, but, in myelinated fibers, Myelin decreases capacitance and increases electrical resistance across the cell membrane. Thus, myelination helps prevent the current from leaving the axon. It has been suggested that myelin permits larger body size by maintaining agile communication between distant body parts, myelinated fibers lack voltage-gated ion channels along the myelinated internodes, exposing them only at the nodes of Ranvier. Here, they are far more abundantly. Myelinated fibers succeed in reducing sodium leakage into the extracellular fluid and this increases sodium’s ability to travel along the axon more freely
9.
Ancient Greek
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Ancient Greek includes the forms of Greek used in ancient Greece and the ancient world from around the 9th century BC to the 6th century AD. It is often divided into the Archaic period, Classical period. It is antedated in the second millennium BC by Mycenaean Greek, the language of the Hellenistic phase is known as Koine. Koine is regarded as a historical stage of its own, although in its earliest form it closely resembled Attic Greek. Prior to the Koine period, Greek of the classic and earlier periods included several regional dialects, Ancient Greek was the language of Homer and of fifth-century Athenian historians, playwrights, and philosophers. It has contributed many words to English vocabulary and has been a subject of study in educational institutions of the Western world since the Renaissance. This article primarily contains information about the Epic and Classical phases of the language, Ancient Greek was a pluricentric language, divided into many dialects. The main dialect groups are Attic and Ionic, Aeolic, Arcadocypriot, some dialects are found in standardized literary forms used in literature, while others are attested only in inscriptions. There are also several historical forms, homeric Greek is a literary form of Archaic Greek used in the epic poems, the Iliad and Odyssey, and in later poems by other authors. Homeric Greek had significant differences in grammar and pronunciation from Classical Attic, the origins, early form and development of the Hellenic language family are not well understood because of a lack of contemporaneous evidence. Several theories exist about what Hellenic dialect groups may have existed between the divergence of early Greek-like speech from the common Proto-Indo-European language and the Classical period and they have the same general outline, but differ in some of the detail. The invasion would not be Dorian unless the invaders had some relationship to the historical Dorians. The invasion is known to have displaced population to the later Attic-Ionic regions, the Greeks of this period believed there were three major divisions of all Greek people—Dorians, Aeolians, and Ionians, each with their own defining and distinctive dialects. Often non-west is called East Greek, Arcadocypriot apparently descended more closely from the Mycenaean Greek of the Bronze Age. Boeotian had come under a strong Northwest Greek influence, and can in some respects be considered a transitional dialect, thessalian likewise had come under Northwest Greek influence, though to a lesser degree. Most of the dialect sub-groups listed above had further subdivisions, generally equivalent to a city-state and its surrounding territory, Doric notably had several intermediate divisions as well, into Island Doric, Southern Peloponnesus Doric, and Northern Peloponnesus Doric. The Lesbian dialect was Aeolic Greek and this dialect slowly replaced most of the older dialects, although Doric dialect has survived in the Tsakonian language, which is spoken in the region of modern Sparta. Doric has also passed down its aorist terminations into most verbs of Demotic Greek, by about the 6th century AD, the Koine had slowly metamorphosized into Medieval Greek
10.
Neurotransmission
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Neurotransmission is essential for the process of communication between two neurons. In response to an action potential or graded electrical potential. The released neurotransmitter may then move across the synapse to be detected by, binding of neurotransmitters may influence the postsynaptic neuron in either an inhibitory or excitatory way. Neurons form elaborate networks through which nerve impulses travel, each neuron has as many as 15,000 connections with other neurons. Neurons do not touch each other, instead, neurons interact at close contact points called synapses, a neuron transports its information by way of an action potential. When the nerve impulse arrives at the synapse, it may cause the release of neurotransmitters, the postsynaptic neuron may receive inputs from many additional neurons, both excitatory and inhibitory. Excitatory inputs bring a neuron closer to threshold, while inhibitory inputs bring the neuron farther from threshold, an action potential is an all-or-none event, neurons whose membranes have not reached threshold will not fire, while those that do must fire. Once the action potential is initiated, it will propagate along the axon and this can take place in the cell body, in the axon, or in the axon terminal. Storage of the neurotransmitter in storage granules or vesicles in the axon terminal, calcium enters the axon terminal during an action potential, causing release of the neurotransmitter into the synaptic cleft. After its release, the transmitter binds to and activates a receptor in the postsynaptic membrane, the neurotransmitter is either destroyed enzymatically, or taken back into the terminal from which it came, where it can be reused, or degraded and removed. Neurotransmitters are spontaneously packed in vesicles and released in individual quanta-packets independently of presynaptic action potentials and this slow release is detectable and produces micro-inhibitory or micro-excitatory effects on the postsynaptic neuron. An action potential briefly amplifies this process, neurotransmitter containing vesicles cluster around active sites, and after they have been released may be recycled by one of three proposed mechanism. The first proposed mechanism involves partial opening and then re-closing of the vesicle, the second two involve the full fusion of the vesicle with the membrane, followed by recycling, or recycling into the endosome. The vesicle exocytosis is through to be driven by a complex called SNARE. Once released, a neurotransmitter enters the synapse and encounters receptors, neurotransmitters receptors can either be inotropic or g protein coupled. Inotropic receptors allow for ions to pass through when agonized by a ligand, the main model involves a receptor composed of multiple subunits that allow for coordination of ion preference. G protein coupled receptors, also called metabotropic receptors, when bound to by a ligand undergo conformational changes yielding in intracellular response, termination of neurotransmitter activity is usually done by a transporter, however enzymatic deactivation is also plausible. Each neuron connects with other neurons, receiving numerous impulses from them
11.
Synapse
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In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another neuron. Some authors generalize this concept to include the communication from a neuron to any cell type, such as to a motor cell. Santiago Ramón y Cajal proposed that neurons are not continuous throughout the body, yet still communicate with each other, an idea known as the neuron doctrine. Synapses are essential to function, neurons are cells that are specialized to pass signals to individual target cells. At a synapse, the membrane of the signal-passing neuron comes into close apposition with the membrane of the target cell. Both the presynaptic and postsynaptic sites contain extensive arrays of a molecular machinery that link the two together and carry out the signaling process. In many synapses, the part is located on an axon. Astrocytes also exchange information with the neurons, responding to synaptic activity and, in turn. The neurotransmitter may initiate a response or a secondary messenger pathway that may either excite or inhibit the postsynaptic neuron. Chemical synapses can be classified according to the released, glutamatergic, GABAergic, cholinergic. Because of the complexity of receptor signal transduction, chemical synapses can have effects on the postsynaptic cell. The main advantage of a synapse is the rapid transfer of signals from one cell to the next. Synaptic communication is distinct from a coupling, in which communication between neurons occurs via indirect electric fields. Synapses can be classified by the type of cellular structures serving as the pre-, the vast majority of synapses in the mammalian nervous system are classical axo-dendritic synapses, however, a variety of other arrangements exist. These include but are not limited to axo-axonic, dendro-dendritic, axo-secretory, somato-dendritic, dendro-somatic, the axon can synapse onto a dendrite, onto a cell body, or onto another axon or axon terminal, as well as into the bloodstream or diffusely into the adjacent nervous tissue. It is widely accepted that the plays a role in the formation of memory. The strength of two connected neural pathways is thought to result in the storage of information, resulting in memory and this process of synaptic strengthening is known as long-term potentiation. By altering the release of neurotransmitters, the plasticity of synapses can be controlled in the presynaptic cell, the postsynaptic cell can be regulated by altering the function and number of its receptors
12.
Action potential
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In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of cells, called excitable cells, which include neurons, muscle cells. In other types of cells, their function is to activate intracellular processes. In muscle cells, for example, a potential is the first step in the chain of events leading to contraction. In beta cells of the pancreas, they provoke release of insulin, action potentials in neurons are also known as nerve impulses or spikes, and the temporal sequence of action potentials generated by a neuron is called its spike train. A neuron that emits an action potential is often said to fire, action potentials are generated by special types of voltage-gated ion channels embedded in a cells plasma membrane. When the channels open they allow a flow of sodium ions, which changes the electrochemical gradient. This then causes more channels to open, producing an electric current across the cell membrane. The process proceeds explosively until all of the ion channels are open. The rapid influx of ions causes the polarity of the plasma membrane to reverse. As the sodium channels close, sodium ions can no longer enter the neuron, potassium channels are then activated, and there is an outward current of potassium ions, returning the electrochemical gradient to the resting state. After an action potential has occurred, there is a transient negative shift, in animal cells, there are two primary types of action potentials. One type is generated by voltage-gated sodium channels, the other by voltage-gated calcium channels, sodium-based action potentials usually last for under one millisecond, whereas calcium-based action potentials may last for 100 milliseconds or longer. In some types of neurons, slow calcium spikes provide the force for a long burst of rapidly emitted sodium spikes. In cardiac muscle cells, on the hand, an initial fast sodium spike provides a primer to provoke the rapid onset of a calcium spike. Nearly all cell membranes in animals, plants and fungi maintain a voltage difference between the exterior and interior of the cell, called the membrane potential. A typical voltage across a cell membrane is –70 mV. In most types of cells the membrane potential usually stays fairly constant, some types of cells, however, are electrically active in the sense that their voltages fluctuate over time
13.
Morphology (biology)
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Morphology is a branch of biology dealing with the study of the form and structure of organisms and their specific structural features. This includes aspects of the appearance, i. e. external morphology, as well as the form and structure of the internal parts like bones and organs. This is in contrast to physiology, which deals primarily with function, Morphology is a branch of life science dealing with the study of gross structure of an organism or taxon and its component parts. The word morphology is from the Ancient Greek don, morphé, meaning form, among other important theorists of morphology are Lorenz Oken, Georges Cuvier, Étienne Geoffroy Saint-Hilaire, Richard Owen, Karl Gegenbaur and Ernst Haeckel. In English-speaking countries, the term molecular morphology has been used for time for describing the structure of compound molecules, such as polymers. Comparative Morphology is analysis of the patterns of the locus of structures within the plan of an organism. Functional Morphology is the study of the relationship between the structure and function of morphological features, experimental Morphology is the study of the effects of external factors upon the morphology of organisms under experimental conditions, such as the effect of genetic mutation. Anatomy is a branch of morphology that deals with the structure of organisms, most taxa differ morphologically from other taxa. Typically, closely related taxa differ much less than more distantly related ones, cryptic species are species which look very similar, or perhaps even outwardly identical, but are reproductively isolated. Conversely, sometimes unrelated taxa acquire a similar appearance as a result of convergent evolution or even mimicry, in addition, there can be morphological differences within a species, such as in Apoica flavissima where queens are significantly smaller than workers. A further problem with relying on morphological data is that what may appear, morphologically speaking, the significance of these differences can be examined through the use of allometric engineering in which one or both species are manipulated to phenocopy the other species. Invention and development of microscopy enable the observation of 3-D cell morphology with both spatial and temporal resolution. The dynamic processes of cell morphology which are controlled by a complex system play an important role in varied important biological process, such as immune. Comparative anatomy Insect morphology Morphometrics Neuromorphology Phenetics Phenotype Phenotypic plasticity Plant morphology
14.
Dendritic spine
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A dendritic spine is a small membranous protrusion from a neurons dendrite that typically receives input from a single axon at the synapse. Dendritic spines serve as a site for synaptic strength and help transmit electrical signals to the neurons cell body. Most spines have a head, and a thin neck that connects the head of the spine to the shaft of the dendrite. The dendrites of a neuron can contain hundreds to thousands of spines. In addition to providing an anatomical substrate for memory storage and synaptic transmission. Dendritic spines were first described at the end of the 19th century by Santiago Ramón y Cajal on cerebellar neurons, Ramón y Cajal then proposed that dendritic spines could serve as contacting sites between neurons. This was demonstrated more than 50 years later thanks to the emergence of electron microscopy, until the development of confocal microscopy on living tissues, it was commonly admitted that spines were formed during embryonic development and then would remain stable after birth. In this paradigm, variations of synaptic weight were considered as sufficient to explain memory processes at the cellular level. But since about a decade ago, new techniques of confocal microscopy demonstrated that dendritic spines are indeed motile and dynamic structures that undergo a constant turnover, Dendritic spines usually receive excitatory input from axons although sometimes both inhibitory and excitatory connections are made onto the same spine head. Dendritic spines occur at a density of up to 5 spines/1 µm stretch of dendrite, Dendritic spines are small with spine head volumes ranging 0.01 µm3 to 0.8 µm3. Spines with strong synaptic contacts typically have a large spine head, the most notable classes of spine shape are thin, stubby, mushroom, and branched. Electron microscopy studies have shown there is a continuum of shapes between these categories. The variable spine shape and volume is thought to be correlated with the strength, Dendritic spines express glutamate receptors on their surface. The TrkB receptor for BDNF is also expressed on the spine surface, the tip of the spine contains an electron-dense region referred to as the postsynaptic density. One-half of the axons and dendritic spines are physically tethered by calcium-dependent cadherin. Glutamate receptors are localized to the density, and are anchored by cytoskeletal elements to the membrane. Signalling from GluRs is mediated by the presence of an abundance of proteins, especially kinases and these include calcium-dependent calmodulin, CaMKII, PKC, PKA, Protein Phosphatase-1, and Fyn tyrosine kinase. Certain signallers, such as CaMKII, are upregulated in response to activity, spines are particularly advantageous to neurons by compartmentalizing biochemical signals
15.
Long-term potentiation
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In neuroscience, long-term potentiation is a persistent strengthening of synapses based on recent patterns of activity. These are patterns of activity that produce a long-lasting increase in signal transmission between two neurons. The opposite of LTP is long-term depression, which produces a decrease in synaptic strength. It is one of several phenomena underlying synaptic plasticity, the ability of synapses to change their strength. As memories are thought to be encoded by modification of synaptic strength, LTP is widely considered one of the cellular mechanisms that underlies learning. LTP was discovered in the hippocampus by Terje Lømo in 1966 and has remained a popular subject of research since. Many modern LTP studies seek to understand its basic biology. Still others try to develop methods, pharmacologic or otherwise, of enhancing LTP to improve learning, LTP is also a subject of clinical research, for example, in the areas of Alzheimers disease and addiction medicine. With this realization came the need to explain how memories could form in the absence of new neurons, the Spanish neuroanatomist Santiago Ramón y Cajal was among the first to suggest a mechanism of learning that did not require the formation of new neurons. In his 1894 Croonian Lecture, he proposed that memories might instead be formed by strengthening the connections between existing neurons to improve the effectiveness of their communication. These skills would not come until the half of the 20th century. LTP was first observed by Terje Lømo in 1966 in the Oslo, Norway, there, Lømo conducted a series of neurophysiological experiments on anesthetized rabbits to explore the role of the hippocampus in short-term memory. Lømos experiments focused on connections, or synapses, from the perforant pathway to the dentate gyrus and these experiments were carried out by stimulating presynaptic fibers of the perforant pathway and recording responses from a collection of postsynaptic cells of the dentate gyrus. As expected, a pulse of electrical stimulation to fibers of the perforant pathway caused excitatory postsynaptic potentials in cells of the dentate gyrus. When such a train of stimuli was applied, subsequent single-pulse stimuli elicited stronger, Timothy Bliss, who joined the Andersen laboratory in 1968, collaborated with Lømo and in 1973 the two published the first characterization of long-lasting potentiation in the rabbit hippocampus. Bliss and Tony Gardner-Medwin published a report of long-lasting potentiation in the awake animal which appeared in the same issue as the Bliss. In 1975, Douglas and Goddard proposed long-term potentiation as a new name for the phenomenon of long-lasting potentiation, Andersen suggested that the authors chose long-term potentiation perhaps because of its easily pronounced acronym, LTP. The physical and biological mechanism of LTP is still not understood, still others have proposed re-arranging or synchronizing the relationship between receptor regulation, LTP, and synaptic strength
16.
Wilhelm His Sr.
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Wilhelm His, Sr. was a Swiss anatomist and professor who invented the microtome. His came from a family and studied medicine in Basel, Berlin, Würzburg, Bern, Vienna. He received a doctorate in 1854, and in 1856 received the habilitation in Basel,1857, at the age of 26, he became professor of anatomy and physiology at the University of Basel. In 1872 he took up a call from University of Leipzig to become professor there and his made a most significant theoretical contribution when he specifically rejected all forms of soft inheritance. The passage runs, Until it has been refuted, I stand by the statement that characters can not be inherited that were acquired during the lifetime of the individual, the passage comes from his W.1874. Unsere Körperform und das physiologische Problem ihrer Enstehung, the historical significance is that it was not until 1883 that August Weismann made a similar declaration. His was elected a member of the Royal Swedish Academy of Sciences in 1892, to begin with, His collected tissue depth data by using a thin needle bearing a small rubber piece that would ride upward on the needle as it was pushed into the tissue of cadavers. The needle was placed at angles to the bone and pressed into the tissue until its point touched the bone. The displacement of the rubber was measured and recorded for 15 specific locations on 24 male, peipert JF, Roberts CS. Wilhelm His, Sr. s finding of Johann Sebastian Bach. Wilhelm His Sr. — embryologist and anatomist, the Embryograph of Wilhelm His, Hartnacks Drawing Apparatus
17.
Otto Deiters
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Otto Friedrich Karl Deiters was a German neuroanatomist. He was born in Bonn, studied at the University of Bonn and he is remembered for his microscopic research of the brain and spinal cord. Around 1860, Deiters provided the most comprehensive description of a cell that was known to exist at the time. He identified the cells axon, which he called a cylinder, and its dendrites. He postulated that dendrites must fuse to form a continuous network and his name is lent to the nucleus of Deiters, also called the lateral vestibular nucleus, and to Deiters cells, structures that are associated with outer hair cells in the cochlea of the inner ear. Deiters died in 1863 from typhoid fever at the age of 29, after his death, his work pertaining to nerve cells of the spinal cord was edited and published by anatomist Max Schultze. com article on Deiters cell
18.
Kenneth Stewart Cole
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Kenneth Stewart Cole was an American biophysicist described by his peers as a pioneer in the application of physical science to biology. Cole was awarded the National Medal of Science in 1967 and he was born on July 10,1900 in Ithaca, New York to Charles Nelson Cole, an instructor in Latin at Cornell University and Mabel Stewart. In 1902 the family moved to Oberlin, Ohio, when his father took a post at Oberlin College and his father would later become the Dean. Kenneths mother was, and Cole graduated from Oberlin College in 1922 and he spent summers working at the General Electric laboratory in Schenectady, New York. In 1932, Cole married Elizabeth Evans Roberts, an attorney and he had also been associated with the Presbyterian Hospital, and the Guggenheim Foundation for Advanced Study at Princeton University and the University of Chicago. From 1949 to 1954 he was the director of the Naval Medicine Research Institute in Bethesda. In 1954 he became chief of the laboratory of biophysics of the National Institute of Neurological Diseases and he achieved advances that led to the sodium theory of nerve transmission that later won Nobel Prizes for Alan L. Hodgkin and Andrew F. Huxley in 1947. Cole was elected a member of the National Academy of Sciences in 1956, and he was awarded the National Medal of Science in 1967, the award citation, read, As a result, we know far more about how the nervous system functions. In 1972 he was made a member of the Royal Society of London, the Biophysical Society awards the Kenneth S. Cole medal to a scientist studying cell membranes. In 1980 he became a professor of the Department of Neurosciences at the Scripps Institute of Oceanography in San Diego. He had a son, Roger Braley Cole, and a daughter and he died on April 18,1984 in La Jolla, California. The parameter α can assume values between 0 and 1, the former value giving the result of Debye for polar dielectrics. This expression requires that the locus of the constant in the complex plane be a circular arc with end points on the axis of reals. It is worth emphasizing that the Cole–Cole model is an model of the measured data. It has been applied to a wide variety of tissues over the past 60 years. Several references in the use a form of the Cole equation written in terms of impedance instead of a complex permittivity. The impedance Z is given by, Z = R ∞ + R0 − R ∞1 +1 − α Where R0 and R ∞ are the resistances at zero frequency and infinity, F c is often referred to as the characteristic frequency. It should be emphasized that the frequency is not the same when the analysis is carried out in terms of the complex permittivity
19.
Alan Lloyd Hodgkin
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Sir Alan Lloyd Hodgkin OM KBE PRS was an English physiologist and biophysicist, who shared the 1963 Nobel Prize in Physiology or Medicine with Andrew Huxley and John Eccles. Hodgkin was born in Banbury, Oxfordshire, to George Hodgkin and his father died of dysentery in Baghdad in 1918. His mother was remarried to Lionel Smith, with whom they lived and he was educated at The Downs School near Malvern, Greshams School, and Trinity College, Cambridge. In 1930, he was the winner of a medal in the Public Schools Essay Competition organised by the Royal Society for the Protection of Birds. Earlier, in March 1941, Hodgkin had flown on the test flight of a Bristol Blenheim fitted with the first airborne radar system. As the war ended in 1945, he joined the faculty of department in Cambridge University. He was the Foulerton Professor of the Royal Society between 1951 and 1969 and he served on the Royal Society Council from 1958 to 1960 and on the Medical Research Council from 1959 to1963. He was foreign secretary of the Physiological Society from 1961 to 1967 and he was appointed the John Humphrey Plummer Professor of Biophysics at Cambridge University in 1970. He also held administrative posts such as Chancellor, University of Leicester, from 1971 to 1984. Research was interrupted by World War II but after resuming their experimental work in Plymouth, in addition Hodgkin and Huxleys findings led them to hypothesize the existence of ion channels on cell membranes, which were confirmed only decades later. Confirmation of ion channels came with the development of the patch clamp leading to a Nobel prize in 1991 for Erwin Neher and Bert Sakmann, Hodgkin was also the discoverer of cell membrane depolarisation sequence now known as the Hodgkin cycle. Hodgkin was knighted in 1972 and appointed to the Order of Merit in 1973 and he was elected President of the Marine Biological Association of the United Kingdom in 1966. From 1970 to 1975 he was President of the Royal Society, the Royal Society awarded him its Royal Medal in 1958 and Copley Medal in 1965. A portrait of Hodgkin by Michael Noakes hangs in Trinity Colleges collection, Alan Hodgkin married Marion Rous in 1944, whom he met while at Rockefeller Institute in 1938. She was the daughter of an American pathologist, Francis Peyton Rous and she became Childrens Book Editor at Macmillan Publishing Company and a successful writer of childrens literature, including Young Winters Tales and Dead Indeed. They had three daughters, Sarah, Deborah, and Rachel, and a son Jonathan, Jonathan Hodgkin became a molecular biologist at Cambridge University. Deborah Hodgkin is also a successful psychologist, thomas Hodgkin, who diagnosed Hodgkins Lymphoma, was Alan Hodgkins ancestor. Alan Hodgkin died in 1998 at Cambridge, hodgkin–Huxley model The Master of Trinity at Trinity College, Cambridge Nobel biography of Hodgkin BBC obituary Speech at Nobel banquet,1963 Action Potential Paper Imperial War Museum Interview
20.
Andrew Huxley
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Sir Andrew Fielding Huxley OM PRS was a Nobel Prize-winning English physiologist and biophysicist. He was born into the prominent Huxley family, after graduating from Westminster School in Central London, from where he won a scholarship to Trinity College, Cambridge, he joined Alan Lloyd Hodgkin to study nerve impulses. Their eventual discovery of the basis for propagation of nerve impulses earned them the Nobel Prize in Physiology or Medicine in 1963 and they made their discovery from the giant axon of the Atlantic squid. Soon after the outbreak of the Second World War, Huxley was recruited by the British Anti-Aircraft Command, after the war he resumed research at The University of Cambridge, where he developed interference microscopy that would be suitable for studying muscle fibres. In 1952 he was joined by a German physiologist Rolf Niedergerke, together they discovered in 1954 the mechanism of muscle contraction, popularly called the sliding filament theory, which is the foundation of our modern understanding of muscle mechanics. In 1960 he became head of the Department of Physiology at University College London and he was elected a Fellow of the Royal Society in 1955, and President in 1980. The Royal Society awarded him the Copley Medal in 1973 for his contributions to the understanding of nerve impulses. He was conferred a Knight Bachelor by Queen Elizabeth II in 1974 and he was a fellow of Trinity College, Cambridge, until his death. Huxley was born in Hampstead, London, England, on 22 November 1917, when he was about 12, Andrew and his brother David were given a lathe by their parents. Andrew soon became proficient at designing, making and assembling mechanical objects of all kinds and he used these practical skills throughout his career, building much of the specialized equipment he needed for his research. It was also in his teens that he formed his lifelong interest in microscopy. He was educated at University College School and Westminster School in Central London and he graduated and won a scholarship to Trinity College, Cambridge, to read natural sciences. He had intended to become an engineer but switched to physiology after taking the subject to fulfill an elective, having entered Cambridge in 1935, Huxley graduated with a bachelors degree in 1938. In 1939, Alan Lloyd Hodgkin returned from the USA to take up a fellowship at Trinity College, Hodgkin was interested in the transmission of electrical signals along nerve fibres. Beginning in 1935 in Cambridge, he had made preliminary measurements on frog sciatic nerves suggesting that the view of the nerve as a simple. Hodgkin invited Huxley to join him researching the problem, one major problem was that the small size of most neurons made it extremely difficult to study them using the techniques of the time. They overcame this by working at the Marine Biological Association laboratory in Plymouth using the giant axon of the longfin inshore squid, which have the largest neurons known. In 1939, they published a short paper in Nature reporting on the work done in Plymouth
21.
Nobel Prize
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The Nobel Prize is a set of annual international awards bestowed in a number of categories by Swedish and Norwegian institutions in recognition of academic, cultural, or scientific advances. The will of the Swedish inventor Alfred Nobel established the prizes in 1895, the prizes in Chemistry, Literature, Peace, Physics, and Physiology or Medicine were first awarded in 1901. Medals made before 1980 were struck in 23 carat gold, between 1901 and 2016, the Nobel Prizes and the Prize in Economic Sciences were awarded 579 times to 911 people and organisations. With some receiving the Nobel Prize more than once, this makes a total of 23 organisations, the prize ceremonies take place annually in Stockholm, Sweden. Each recipient, or laureate, receives a medal, a diploma. The Nobel Prize is widely regarded as the most prestigious award available in the fields of literature, medicine, physics, chemistry, peace, and economics. The prize is not awarded posthumously, however, if a person is awarded a prize and dies before receiving it, though the average number of laureates per prize increased substantially during the 20th century, a prize may not be shared among more than three people. Alfred Nobel was born on 21 October 1833 in Stockholm, Sweden and he was a chemist, engineer, and inventor. In 1894, Nobel purchased the Bofors iron and steel mill and this invention was a precursor to many smokeless military explosives, especially the British smokeless powder cordite. As a consequence of his patent claims, Nobel was eventually involved in a patent infringement lawsuit over cordite, Nobel amassed a fortune during his lifetime, with most of his wealth from his 355 inventions, of which dynamite is the most famous. In 1888, Nobel was astonished to read his own obituary, titled The merchant of death is dead, as it was Alfreds brother Ludvig who had died, the obituary was eight years premature. The article disconcerted Nobel and made him apprehensive about how he would be remembered and this inspired him to change his will. On 10 December 1896, Alfred Nobel died in his villa in San Remo, Italy, Nobel wrote several wills during his lifetime. He composed the last over a year before he died, signing it at the Swedish–Norwegian Club in Paris on 27 November 1895, Nobel bequeathed 94% of his total assets,31 million SEK, to establish the five Nobel Prizes. Because of skepticism surrounding the will, it was not until 26 April 1897 that it was approved by the Storting in Norway. The executors of Nobels will, Ragnar Sohlman and Rudolf Lilljequist, formed the Nobel Foundation to take care of Nobels fortune, Nobels instructions named a Norwegian Nobel Committee to award the Peace Prize, the members of whom were appointed shortly after the will was approved in April 1897. Soon thereafter, the other prize-awarding organisations were designated or established and these were Karolinska Institutet on 7 June, the Swedish Academy on 9 June, and the Royal Swedish Academy of Sciences on 11 June. The Nobel Foundation reached an agreement on guidelines for how the prizes should be awarded, and, in 1900, in 1905, the personal union between Sweden and Norway was dissolved
22.
Camillo Golgi
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Camillo Golgi was an Italian physician, biologist, pathologist, scientist, and Nobel laureate. Several structures and phenomena in anatomy and physiology are named for him, including the Golgi apparatus, the Golgi tendon organ and he is recognized as the greatest neuroscientist and biologist of his time. Camillo Golgi was born in July 1843 in the village of Corteno, in the province of Brescia, the village is now named Corteno Golgi in his honour. His father was a physician and district medical officer, Golgi studied at the University of Pavia, where he worked in the experimental pathology laboratory under Giulio Bizzozero, who elucidated the properties of bone marrow. He spent much of his studying the central nervous system. Tissue staining techniques in the half of the 19th century were inadequate for studying nervous tissue. While working as medical officer in a psychiatric hospital, he experimented with metal impregnation of nervous tissue. He discovered a method of staining nervous tissue that would stain a limited number of cells at random in their entirety and this enabled him to view the paths of nerve cells in the brain for the first time. He called his discovery the black reaction, which received his name. The reason for the staining is still not understood. The black reaction consisted in fixing silver chromate particles to the neurilemma by reacting silver nitrate with potassium dichromate. This resulted in a black deposit on the soma as well as on the axon and all dendrites, providing an exceedingly clear. The ability to visualize separate neurons led to the acceptance of the neuron doctrine. However, Golgi himself was led to a conviction that nervous system is a network, not of separate cells. He supported this theory even in his Nobel lecture. In addition to this discovery, Golgi discovered a tendon sensory organ that bears his name, using his staining technique, Golgi identified the intracellular reticular apparatus in 1898 which bears his name, the Golgi apparatus. In renal physiology Golgi is renowned for being the first to show that the distal tubulus of the returns to its originating glomerulus. Golgi, together with Santiago Ramón y Cajal, received the Nobel Prize in Physiology or Medicine in 1906 for his studies of the structure of the nervous system, in 1900 he was named senator by King Umberto I
23.
Voltage
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Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential energy between two points per unit electric charge. The voltage between two points is equal to the work done per unit of charge against an electric field to move the test charge between two points. This is measured in units of volts, voltage can be caused by static electric fields, by electric current through a magnetic field, by time-varying magnetic fields, or some combination of these three. A voltmeter can be used to measure the voltage between two points in a system, often a reference potential such as the ground of the system is used as one of the points. A voltage may represent either a source of energy or lost, used, given two points in space, x A and x B, voltage is the difference in electric potential between those two points. Electric potential must be distinguished from electric energy by noting that the potential is a per-unit-charge quantity. Like mechanical potential energy, the zero of electric potential can be chosen at any point, so the difference in potential, i. e. the voltage, is the quantity which is physically meaningful. The voltage between point A to point B is equal to the work which would have to be done, per unit charge, against or by the electric field to move the charge from A to B. The voltage between the two ends of a path is the energy required to move a small electric charge along that path. Mathematically this is expressed as the integral of the electric field. In the general case, both an electric field and a dynamic electromagnetic field must be included in determining the voltage between two points. Historically this quantity has also called tension and pressure. Pressure is now obsolete but tension is used, for example within the phrase high tension which is commonly used in thermionic valve based electronics. Voltage is defined so that negatively charged objects are pulled towards higher voltages, therefore, the conventional current in a wire or resistor always flows from higher voltage to lower voltage. Current can flow from lower voltage to higher voltage, but only when a source of energy is present to push it against the electric field. This is the case within any electric power source, for example, inside a battery, chemical reactions provide the energy needed for ion current to flow from the negative to the positive terminal. The electric field is not the only factor determining charge flow in a material, the electric potential of a material is not even a well defined quantity, since it varies on the subatomic scale. A more convenient definition of voltage can be found instead in the concept of Fermi level, in this case the voltage between two bodies is the thermodynamic work required to move a unit of charge between them
24.
Cable theory
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Classical cable theory uses mathematical models to calculate the electric current along passive neurites, particularly the dendrites that receive synaptic inputs at different sites and times. Estimates are made by modeling dendrites and axons as cylinders composed of segments with capacitances c m, the capacitance of a neuronal fiber comes about because electrostatic forces are acting through the very thin lipid bilayer. The resistance in series along the fiber r l is due to the significant resistance to movement of electric charge. Cable theory in neuroscience has roots leading back to the 1850s. The models resembled the partial differential equations used by Fourier to describe heat conduction in a wire, the 1870s saw the first attempts by Hermann to model neuronal electrotonic potentials also by focusing on analogies with heat conduction. Further mathematical theories of nerve fiber conduction based on cable theory were developed by Cole and Hodgkin, Offner et al. two key papers from this era are those of Davis and Lorente de Nó and Hodgkin and Rushton. The 1950s saw improvements in techniques for measuring the activity of individual neurons. Thus cable theory became important for analyzing data collected from intracellular microelectrode recordings, scientists like Coombs, Eccles, Fatt, Frank, Fuortes and others now relied heavily on cable theory to obtain functional insights of neurons and for guiding them in the design of new experiments. Note, various conventions of rm exist, here rm and cm, as introduced above, are measured per membrane-length unit. Thus rm is measured in ohm·meters and cm in farads per meter and this is in contrast to Rm and Cm, which represent the specific resistance and capacitance respectively of one unit area of membrane. A current injected into the fiber at position x =0 would move along the inside of the fiber unchanged. The more holes, the faster the water escape from the hose. Similarly, in an axon, some of the current traveling longitudinally through the axoplasm will escape through the membrane, if im is the current escaping through the membrane per length unit, m, then the total current escaping along y units must be y·im. The capacitance will cause a flow of charge towards the membrane on the side of the cytoplasm and this current is usually referred to as displacement current The flow will only take place as long as the membranes storage capacity has not been reached. I c can then be expressed as, where c m is the membranes capacitance, combining equations and gives a first version of a cable equation, which is a second-order partial differential equation. By a simple rearrangement of equation it is possible to make two important terms appear, namely the length constant denoted λ and the time constant denoted τ, the following sections focus on these terms. The length constant, λ, is a parameter that indicates how far a stationary current will influence the voltage along the cable, the larger the value of λ, the farther the charge will flow. The higher the resistance, r l, the smaller the value of λ, the harder it will be for current to travel through the axoplasm
25.
Dendritic spike
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In neurophysiology, a dendritic spike refers to an action potential generated in the dendrite of a neuron. Dendrites are branched extensions of a neuron and they receive electrical signals emitted from projecting neurons and transfer these signals to the cell body, or soma. Dendritic signaling has traditionally viewed as a passive mode of electrical signaling. However, a body of evidence now makes it clear that dendrites are active neuronal structures. Dendrites contain voltage-gated ion channels giving them the ability to generate action potentials, dendritic spikes have been recorded in numerous types of neurons in the brain and are thought to have great implications in neuronal communication, memory, and learning. They are one of the factors in long-term potentiation. A dendritic spike is initiated in the manner as that of an axonal action potential. Depolarization of the membrane causes sodium and potassium voltage-gated ion channels to open. The influx of ions causes an increase in voltage. If the voltage increases past a threshold, the sodium current activates other voltage-gated sodium channels transmitting a current along the dendrite. Dendritic spikes can be generated through both sodium and calcium voltage-gated channels, dendritic spikes usually transmit signals at a much slower rate than axonal action potentials. Local voltage thresholds for dendritic spike initiation are usually higher than that of action potential initiation in the axon, therefore, voltage-gated sodium channels are proteins found in the membrane of neurons. When electrically activated, they allow the movement of ions across a plasma membrane. These channels are responsible for propagation of signals in nerve cells. Voltage-gated sodium channels can be divided into two subunits, alpha and beta, a variety of alpha subunit voltage-gated sodium channels have been identified. Voltage-gated sodium channels found in mammals can be divided into three types, Nav1. x, Nav2. x, and Nav3. x, Nav1. x sodium channels are associated with the central nervous system. Nav1.1, Nav2.2, and Nav1.6 are three isoforms of the sodium channels that are present at high levels in the central nervous system of an adult rat brain. These channels have been documented in the axonal membrane of the central nervous system
26.
PubMed Identifier
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PubMed is a free search engine accessing primarily the MEDLINE database of references and abstracts on life sciences and biomedical topics. The United States National Library of Medicine at the National Institutes of Health maintains the database as part of the Entrez system of information retrieval, from 1971 to 1997, MEDLINE online access to the MEDLARS Online computerized database primarily had been through institutional facilities, such as university libraries. PubMed, first released in January 1996, ushered in the era of private, free, home-, the PubMed system was offered free to the public in June 1997, when MEDLINE searches via the Web were demonstrated, in a ceremony, by Vice President Al Gore. Information about the journals indexed in MEDLINE, and available through PubMed, is found in the NLM Catalog. As of 5 January 2017, PubMed has more than 26.8 million records going back to 1966, selectively to the year 1865, and very selectively to 1809, about 500,000 new records are added each year. As of the date,13.1 million of PubMeds records are listed with their abstracts. In 2016, NLM changed the system so that publishers will be able to directly correct typos. Simple searches on PubMed can be carried out by entering key aspects of a subject into PubMeds search window, when a journal article is indexed, numerous article parameters are extracted and stored as structured information. Such parameters are, Article Type, Secondary identifiers, Language, publication type parameter enables many special features. As these clinical girish can generate small sets of robust studies with considerable precision, since July 2005, the MEDLINE article indexing process extracts important identifiers from the article abstract and puts those in a field called Secondary Identifier. The secondary identifier field is to store numbers to various databases of molecular sequence data, gene expression or chemical compounds. For clinical trials, PubMed extracts trial IDs for the two largest trial registries, ClinicalTrials. gov and the International Standard Randomized Controlled Trial Number Register, a reference which is judged particularly relevant can be marked and related articles can be identified. If relevant, several studies can be selected and related articles to all of them can be generated using the Find related data option, the related articles are then listed in order of relatedness. To create these lists of related articles, PubMed compares words from the title and abstract of each citation, as well as the MeSH headings assigned, using a powerful word-weighted algorithm. The related articles function has been judged to be so precise that some researchers suggest it can be used instead of a full search, a strong feature of PubMed is its ability to automatically link to MeSH terms and subheadings. Examples would be, bad breath links to halitosis, heart attack to myocardial infarction, where appropriate, these MeSH terms are automatically expanded, that is, include more specific terms. Terms like nursing are automatically linked to Nursing or Nursing and this important feature makes PubMed searches automatically more sensitive and avoids false-negative hits by compensating for the diversity of medical terminology. The My NCBI area can be accessed from any computer with web-access, an earlier version of My NCBI was called PubMed Cubby
27.
International Standard Book Number
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The International Standard Book Number is a unique numeric commercial book identifier. An ISBN is assigned to each edition and variation of a book, for example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, the method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967 based upon the 9-digit Standard Book Numbering created in 1966, the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108. Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure, however, this can be rectified later. Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines, the ISBN configuration of recognition was generated in 1967 in the United Kingdom by David Whitaker and in 1968 in the US by Emery Koltay. The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108, the United Kingdom continued to use the 9-digit SBN code until 1974. The ISO on-line facility only refers back to 1978, an SBN may be converted to an ISBN by prefixing the digit 0. For example, the edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has SBN340013818 -340 indicating the publisher,01381 their serial number. This can be converted to ISBN 0-340-01381-8, the check digit does not need to be re-calculated, since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with Bookland European Article Number EAN-13s. An ISBN is assigned to each edition and variation of a book, for example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, a 13-digit ISBN can be separated into its parts, and when this is done it is customary to separate the parts with hyphens or spaces. Separating the parts of a 10-digit ISBN is also done with either hyphens or spaces, figuring out how to correctly separate a given ISBN number is complicated, because most of the parts do not use a fixed number of digits. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for country or territory regardless of the publication language. Some ISBN registration agencies are based in national libraries or within ministries of culture, in other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded. In Canada, ISBNs are issued at no cost with the purpose of encouraging Canadian culture. In the United Kingdom, United States, and some countries, where the service is provided by non-government-funded organisations. Australia, ISBNs are issued by the library services agency Thorpe-Bowker
28.
OCLC
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The Online Computer Library Center is a US-based nonprofit cooperative organization dedicated to the public purposes of furthering access to the worlds information and reducing information costs. It was founded in 1967 as the Ohio College Library Center, OCLC and its member libraries cooperatively produce and maintain WorldCat, the largest online public access catalog in the world. OCLC is funded mainly by the fees that libraries have to pay for its services, the group first met on July 5,1967 on the campus of the Ohio State University to sign the articles of incorporation for the nonprofit organization. The group hired Frederick G. Kilgour, a former Yale University medical school librarian, Kilgour wished to merge the latest information storage and retrieval system of the time, the computer, with the oldest, the library. The goal of network and database was to bring libraries together to cooperatively keep track of the worlds information in order to best serve researchers and scholars. The first library to do online cataloging through OCLC was the Alden Library at Ohio University on August 26,1971 and this was the first occurrence of online cataloging by any library worldwide. Membership in OCLC is based on use of services and contribution of data, between 1967 and 1977, OCLC membership was limited to institutions in Ohio, but in 1978, a new governance structure was established that allowed institutions from other states to join. In 2002, the structure was again modified to accommodate participation from outside the United States. As OCLC expanded services in the United States outside of Ohio, it relied on establishing strategic partnerships with networks, organizations that provided training, support, by 2008, there were 15 independent United States regional service providers. OCLC networks played a key role in OCLC governance, with networks electing delegates to serve on OCLC Members Council, in early 2009, OCLC negotiated new contracts with the former networks and opened a centralized support center. OCLC provides bibliographic, abstract and full-text information to anyone, OCLC and its member libraries cooperatively produce and maintain WorldCat—the OCLC Online Union Catalog, the largest online public access catalog in the world. WorldCat has holding records from public and private libraries worldwide. org, in October 2005, the OCLC technical staff began a wiki project, WikiD, allowing readers to add commentary and structured-field information associated with any WorldCat record. The Online Computer Library Center acquired the trademark and copyrights associated with the Dewey Decimal Classification System when it bought Forest Press in 1988, a browser for books with their Dewey Decimal Classifications was available until July 2013, it was replaced by the Classify Service. S. The reference management service QuestionPoint provides libraries with tools to communicate with users and this around-the-clock reference service is provided by a cooperative of participating global libraries. OCLC has produced cards for members since 1971 with its shared online catalog. OCLC commercially sells software, e. g. CONTENTdm for managing digital collections, OCLC has been conducting research for the library community for more than 30 years. In accordance with its mission, OCLC makes its research outcomes known through various publications and these publications, including journal articles, reports, newsletters, and presentations, are available through the organizations website. The most recent publications are displayed first, and all archived resources, membership Reports – A number of significant reports on topics ranging from virtual reference in libraries to perceptions about library funding
29.
Spinal cord
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The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. The brain and spinal cord make up the central nervous system. The spinal cord begins at the bone and extends down to the space between the first and second lumbar vertebrae, it does not extend the entire length of the vertebral column. It is around 45 cm in men and around 43 cm long in women, also, the spinal cord has a varying width, ranging from 13 mm thick in the cervical and lumbar regions to 6.4 mm thick in the thoracic area. The enclosing bony vertebral column protects the relatively shorter spinal cord, the spinal cord is the main pathway for information connecting the brain and peripheral nervous system. The length of the cord is much shorter as compared to the length of the vertebral column. The human spinal cord extends from the magnum and continues through to the conus medullaris near the second lumbar vertebra. It is about 45 cm long in men and around 43 cm in women, ovoid-shaped, the cervical enlargement, located from C5 to T1 spinal segments, is where sensory input comes from and motor output goes to the arms. The lumbar enlargement, located between L1 and S3 spinal segments, handles input and motor output coming from and going to the legs. The spinal cord is continuous with the portion of the medulla. It does not run the length of the vertebral column in adults. It is made of 31 segments that contain sensory nerve root. The first cervical segment is very small and may be absent in most individuals. Nerve roots merge into 31 bilaterally symmetric pairs of spinal nerves, the peripheral nervous system is made up of these spinal roots, nerves, and ganglia. Dorsal root ganglia hold the bodies of dorsal root ganglia in the spinal ganglia related with that spinal segment. Ventral roots only have efferent fibers that arise from motor neurons whose cell bodies are found in the ventral horns of the spinal cord. The spinal cord are protected by three layers of tissue or membranes called meninges, that surround the canal, the dura mater is the outermost layer, and it forms a tough protective coating. Between the dura mater and the bone of the vertebrae is a space called the epidural space
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Nervous tissue
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Nervous tissue is responsible for sending signals to the brain about suicidal thoughts. Nervous tissue is made up of different types of cells, all of which have an axon. Bundles of axons make up the nerves, functions of the nervous system are sensory input, integration, control of muscles and glands, homeostasis, and mental activity. Nervous tissue is composed of neurons, also called nerve cells, typically, nervous tissue is categorized into four types of tissue. In the central system, the tissue types found are grey matter. In the peripheral nervous system, the types are nerves. The tissue is categorized by its neuronal and neuroglial components, neurons are cells with specialized features that allow them to receive and facilitate nerve impulses, or action potentials, across their membrane to the next neuron. They possess a cell body, with cell projections called dendrites. Dendrites are thin, branching projections that receive electrochemical signaling to create a change in voltage in the cell, axons are long projections that carry the action potential away from the cell body toward the next neuron. The bulb-like end of the axon, called the terminal, is separated from the dendrite of the following neuron by a small gap called a synaptic cleft. When the action potential travels to the terminal, neurotransmitters are released across the synapse and bind to the post-synaptic receptors. Neurons are classified both functionally and structurally and they are the major neuron type in the CNS and include interneurons and motor neurons. These are found in the layer of the cerebellum. Neuroglia encompasses the non-neural cells in tissue that provide various crucial supportive functions for neurons. They are smaller than neurons, and vary in structure according to their function, neuroglial cells are classified as follows, Microglial cells, Microglia are macrophage cells that make up the primary immune system for the CNS. They are the smallest neuroglial cell, astrocytes, Star-shaped macroglial cells with many processes found in the CNS. They are the most abundant cell type in the brain, and are intrinsic to a healthy CNS, oligodendrocytes, CNS cells with very few processes. They form myelin sheaths on the axons of a neuron, which are lipid-based insulation that increases the speed at which the action potential, can travel down the axon
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Grey matter
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Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil, glial cells, synapses, and capillaries. The colour difference arises mainly from the whiteness of myelin, in living tissue, grey matter actually has a very light grey colour with yellowish or pinkish hues, which come from capillary blood vessels and neuronal cell bodies. Grey matter refers to unmyelinated neurons and other cells of the nervous system. It is present in the brain, brainstem and cerebellum, grey matter is distributed at the surface of the cerebral hemispheres and of the cerebellum, as well as in the depths of the cerebrum, cerebellar, brainstem. Grey matter in the cord is known as the grey column which travels down the spinal cord distributed in three grey columns that are presented in an H shape. The forward-facing column is the grey column, the rear-facing one is the posterior grey column. The grey matter on the left and right side is connected by the grey commissure, the grey matter in the spinal cord consists of interneurons, as well as cell bodies. Grey matter undergoes development and growth throughout childhood and adolescence, grey matter contains most of the brains neuronal cell bodies. The grey matter includes regions of the involved in muscle control, and sensory perception such as seeing and hearing, memory, emotions, speech, decision making. The grey matter in the cord is split into three grey columns, The anterior grey column contains motor neurons. These synapse with interneurons and the axons of cells that have travelled down the pyramidal tract and these cells are responsible for the movement of muscles. The posterior grey column contains the points where sensory neurons synapse and these receives sensory information from the body, including fine touch, proprioception, and vibration. This information is sent from receptors of the skin, bones and this information is then transmitted in axons up the spinal cord in spinal tracts, including the dorsal column-medial lemniscus tract and the spinothalamic tract. The lateral grey column is the column of the spinal cord. The grey matter of the cord can be divided into different layers. These describe, in general, the purpose of the cells within the matter of the spinal cord at a particular location. High alcohol consumption has been correlated with significant reductions in grey matter volume, in the current edition of the official Latin nomenclature, Terminologia Anatomica, substantia grisea is used for English grey matter. The adjective grisea for grey is however not attested in classical Latin, the adjective grisea is derived from the French word for grey, gris
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White matter
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White matter refers to areas of the central nervous system that are mainly made up of myelinated axons, also called tracts. White matter is named for its relatively light appearance resulting from the content of myelin. However, the tissue of the freshly cut brain appears pinkish white to the eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color in prepared specimens is due to its preservation in formaldehyde. White matter is composed of bundles of myelinated nerve cell projections, which connect various gray matter areas of the brain to each other, and carry nerve impulses between neurons. Myelin acts as an insulator, which allows electrical signals to jump, rather than coursing through the axon, schüz and Braitenberg note As a rough rule, the number of fibres of a certain range of lengths is inversely proportional to their length. White matter in nonelderly adults is 1. 7–3. 6% blood, the other main component of the brain is grey matter, which is composed of neurons. The substantia nigra is a third colored component found in the brain that appears due to higher levels of melanin in dopaminergic neurons than its nearby areas. Note that white matter can sometimes appear darker than grey matter on a slide because of the type of stain used. Cerebral- and spinal white matter do not contain dendrites, neural cell bodies, or shorter axons, white matter forms the bulk of the deep parts of the brain and the superficial parts of the spinal cord. Aggregates of gray matter such as the ganglia and brain stem nuclei are spread within the cerebral white matter. The fluid-filled cerebral ventricles are also located deep within the white matter. Men have more white matter than females both in volume and in length of myelinated axons, at the age of 20, the total length of myelinated fibers in males is 176,000 km while that of a female is 149,000 km. There is a decline in length with age of about 10% each decade such that a man at 80 years of age has 97,200 km. Most of this reduction is due to the loss of thinner fibers, white matter is the tissue through which messages pass between different areas of gray matter within the central nervous system. The white matter is white because of the fatty substance that surrounds the nerve fibers and this myelin is found in almost all long nerve fibers, and acts as an electrical insulation. This is important because it allows the messages to pass quickly from place to place, unlike gray matter, which peaks in development in a persons twenties, the white matter continues to develop, and peaks in middle age. This claim has been disputed in recent years, however, multiple sclerosis is one of the most common diseases which affect white matter
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Association fiber
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Association fibers are axons that connect cortical areas within the same cerebral hemisphere. In human neuroanatomy, axons within the brain, called fibers, can be categorized on the basis of their course and connection into association fibers, projection fibers, and commissural fibers. Many of the association fibers lie immediately beneath the gray substance of the cortex of the hemispheres. Some pass from one wall of the sulcus to the other, the long association fibers connect the more widely separated gyri and are grouped into bundles. They include the following, Diffusion tensor imaging is a method to study the course of association fibers. Interneuron Tractography ancil-672 at NeuroNames ancil-673 at NeuroNames
. PMID 1018277.
