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68-582: They have four main functions: They also play a role in neurotransmission and synaptic connections , and in physiological processes such as breathing . While glia were thought to outnumber neurons by a ratio of 10:1, studies using newer methods and reappraisal of historical quantitative evidence suggests an overall ratio of less than 1:1, with substantial variation between different brain tissues. Glial cells have far more cellular diversity and functions than neurons, and can respond to and manipulate neurotransmission in many ways. Additionally, they can affect both

136-547: A convergence and a divergence of information. First one neuron is influenced by many others, resulting in a convergence of input. When the neuron fires, the signal is sent to many other neurons, resulting in a divergence of output. Many other neurons are influenced by this neuron. Cotransmission is the release of several types of neurotransmitters from a single nerve terminal . At the nerve terminal, neurotransmitters are present within 35–50 nm membrane-encased vesicles called synaptic vesicles . To release neurotransmitters,

204-462: 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 numerous other neurons, receiving numerous impulses from them. Summation is the adding together of these impulses at the axon hillock. If the neuron only gets excitatory impulses, it will generate an action potential. If instead

272-453: A myelin sheath. The myelin sheath insulates the nerve fiber from the extracellular fluid and speeds up signal conduction along the nerve fiber. In the peripheral nervous system, Schwann cells are responsible for myelin production. These cells envelop nerve fibers of the PNS by winding repeatedly around them. This process creates a myelin sheath, which not only aids in conductivity but also assists in

340-409: A rise in intracellular calcium levels) that signal through receptors that are located on the axon terminal of the presynaptic neuron, mainly at GABAergic and glutamatergic synapses . Neurotransmission is regulated by several different factors: the availability and rate-of-synthesis of the neurotransmitter, the release of that neurotransmitter, the baseline activity of the postsynaptic cell,

408-505: A role in the regulation of repair of neurons after injury. In the central nervous system (CNS), glia suppress repair. Glial cells known as astrocytes enlarge and proliferate to form a scar and produce inhibitory molecules that inhibit regrowth of a damaged or severed axon. In the peripheral nervous system (PNS), glial cells known as Schwann cells (or also as neuri-lemmocytes) promote repair. After axonal injury, Schwann cells regress to an earlier developmental state to encourage regrowth of

476-441: Is microglia , which are derived from hematopoietic stem cells . In the adult, microglia are largely a self-renewing population and are distinct from macrophages and monocytes, which infiltrate an injured and diseased CNS. In the central nervous system, glia develop from the ventricular zone of the neural tube. These glia include the oligodendrocytes, ependymal cells, and astrocytes. In the peripheral nervous system, glia derive from

544-420: Is debated. The hippocampus plays a crucial role in the formation of new declarative memories, and it has been theorized that the reason human infants cannot form declarative memories is because they are still undergoing extensive neurogenesis in the hippocampus and their memory-generating circuits are immature. Many environmental factors, such as exercise, stress, and antidepressants have been reported to change

612-420: Is derived from the neural tube , which contains NSCs that will later generate neurons . However, neurogenesis doesn't begin until a sufficient population of NSCs has been achieved. These early stem cells are called neuroepithelial cells (NEC)s, but soon take on a highly elongated radial morphology and are then known as radial glial cells (RGC)s. RGCs are the primary stem cells of the mammalian CNS, and reside in

680-493: Is linked to blood flow in the brain, and that this is what is actually being measured in fMRI . They also have been involved in neuronal circuits playing an inhibitory role after sensing changes in extracellular calcium. Oligodendrocytes are cells that coat axons in the CNS with their cell membrane, forming a specialized membrane differentiation called myelin , producing the myelin sheath . The myelin sheath provides insulation to

748-464: Is most active during embryonic development and is responsible for producing all the various types of neurons of the organism, but it continues throughout adult life in a variety of organisms. Once born, neurons do not divide (see mitosis ), and many will live the lifespan of the animal, except under extraordinary and usually pathogenic circumstances. During embryonic development, the mammalian central nervous system (CNS; brain and spinal cord )

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816-459: Is still developing. In the past, glia had been considered to lack certain features of neurons. For example, glial cells were not believed to have chemical synapses or to release transmitters . They were considered to be the passive bystanders of neural transmission. However, recent studies have shown this to not be entirely true. Some glial cells function primarily as the physical support for neurons. Others provide nutrients to neurons and regulate

884-473: Is the process by which signaling molecules called neurotransmitters are released by the axon terminal of a neuron (the presynaptic neuron), and bind to and react with the receptors on the dendrites of another neuron (the postsynaptic neuron) a short distance away. A similar process occurs in retrograde neurotransmission , where the dendrites of the postsynaptic neuron release retrograde neurotransmitters (e.g., endocannabinoids ; synthesized in response to

952-534: Is thought to be driven by a protein complex called SNARE , that is the target for botulinum toxins . Once released, a neurotransmitter enters the synapse and encounters receptors. Neurotransmitter receptors can either be ionotropic or g protein coupled. Ionotropic 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

1020-601: The PNS frequently assist in regeneration of lost neural functioning, loss of neurons in the CNS does not result in a similar reaction from neuroglia. In the CNS, regrowth will only happen if the trauma was mild, and not severe. When severe trauma presents itself, the survival of the remaining neurons becomes the optimal solution. However, some studies investigating the role of glial cells in Alzheimer's disease are beginning to contradict

1088-460: The enteric system, some related to homeostasis and muscular digestive processes. Microglia are specialized macrophages capable of phagocytosis that protect neurons of the central nervous system . They are derived from the earliest wave of mononuclear cells that originate in yolk sac blood islands early in development, and colonize the brain shortly after the neural precursors begin to differentiate. These cells are found in all regions of

1156-487: The extracellular fluid of the brain, especially surrounding neurons and their synapses . During early embryogenesis , glial cells direct the migration of neurons and produce molecules that modify the growth of axons and dendrites . Some glial cells display regional diversity in the CNS and their functions may vary between the CNS regions. Glia are crucial in the development of the nervous system and in processes such as synaptic plasticity and synaptogenesis . Glia have

1224-400: The habenula whereas the projections from the supramammillary nucleus are known to target the dentate gyrus of the hippocampus. Neurotransmission is genetically associated with other characteristics or features. For example, enrichment analyses of different signaling pathways led to the discovery of a genetic association with intracranial volume. Neurogenesis Neurogenesis is

1292-407: The sympatho -inhibitory action. Thus cannabinoids can inhibit both the noradrenergic and purinergic components of sympathetic neurotransmission. One unusual pair of co-transmitters is GABA and glutamate which are released from the same axon terminals of neurons originating from the ventral tegmental area (VTA), internal globus pallidus , and supramammillary nucleus . The former two project to

1360-604: The CNS, astrocytes (also called astroglia ) have numerous projections that link neurons to their blood supply while forming the blood–brain barrier . They regulate the external chemical environment of neurons by removing excess potassium ions , and recycling neurotransmitters released during synaptic transmission . Astrocytes may regulate vasoconstriction and vasodilation by producing substances such as arachidonic acid , whose metabolites are vasoactive . Astrocytes signal each other using ATP . The gap junctions (also known as electrical synapses ) between astrocytes allow

1428-524: The SVZ of the striatum to the olfactory bulb through the rostral migratory stream (RMS). The migrating neuroblasts in the olfactory bulb become interneurons that help the brain communicate with these sensory cells. The majority of those interneurons are inhibitory granule cells , but a small number are periglomerular cells . In the adult SVZ, the primary neural stem cells are SVZ astrocytes rather than RGCs. Most of these adult neural stem cells lie dormant in

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1496-406: The adult, but in response to certain signals, these dormant cells, or B cells, go through a series of stages, first producing proliferating cells, or C cells. The C cells then produce neuroblasts , or A cells, that will become neurons. Significant neurogenesis also occurs during adulthood in the hippocampus of many mammals, from rodents to some primates , although its existence in adult humans

1564-525: The already neurogenic niches. There is evidence that new neurons are produced in the dentate gyrus of the adult mammalian hippocampus, the brain region important for learning, motivation, memory, and emotion. A study reported that newly made cells in the adult mouse hippocampus can display passive membrane properties, action potentials and synaptic inputs similar to the ones found in mature dentate granule cells. These findings suggested that these newly made cells can mature into more practical and useful neurons in

1632-520: The axon that allows electrical signals to propagate more efficiently. Ependymal cells , also named ependymocytes , line the spinal cord and the ventricular system of the brain. These cells are involved in the creation and secretion of cerebrospinal fluid (CSF) and beat their cilia to help circulate the CSF and make up the blood-CSF barrier . They are also thought to act as neural stem cells. Radial glia cells arise from neuroepithelial cells after

1700-684: The axon, leading to release of neurotransmitters at the synaptic bouton to pass along information to yet another adjacent neuron. Neurotransmitters are spontaneously packed in vesicles and released in individual quanta-packets independently of presynaptic action potentials. This slow release is detectable and produces micro-inhibitory or micro-excitatory effects on the postsynaptic neuron. An action potential briefly amplifies this process. Neurotransmitters containing vesicles cluster around active sites, and after they have been released may be recycled by one of three proposed mechanisms. The first proposed mechanism involves partial opening and then re-closing of

1768-407: The axon. This difference between the CNS and the PNS, raises hopes for the regeneration of nervous tissue in the CNS. For example, a spinal cord may be able to be repaired following injury or severance. Oligodendrocytes are found in the CNS and resemble an octopus: they have bulbous cell bodies with up to fifteen arm-like processes. Each process reaches out to an axon and spirals around it, creating

1836-404: The ayahuasca infusion promotes neurogenesis on the subgranular zone of the dentate gyrus in the hippocampus. A study showed that a low dose (0.1 mg/kg) of psilocybin given to mice increased neurogenesis in the hippocampus 2 weeks after administration, while a high dose (1 mg/kg) significantly decreased neurogenesis. No orally-available drugs are known to elicit neurogenesis outside of

1904-421: The basal ganglia, diencephalon and brainstem combined is 11.35. The total number of glia cells in the human brain is distributed into the different types with oligodendrocytes being the most frequent (45–75%), followed by astrocytes (19–40%) and microglia (about 10% or less). Most glia are derived from ectodermal tissue of the developing embryo , in particular the neural tube and crest . The exception

1972-413: The base of the third ventricle . Drosophila melanogaster , the fruit fly, contains numerous glial types that are functionally similar to mammalian glia but are nonetheless classified differently. In general, neuroglial cells are smaller than neurons. There are approximately 85 billion glia cells in the human brain, about the same number as neurons. Glial cells make up about half the total volume of

2040-449: The brain and spinal cord. Microglial cells are small relative to macroglial cells, with changing shapes and oblong nuclei. They are mobile within the brain and multiply when the brain is damaged. In the healthy central nervous system, microglia processes constantly sample all aspects of their environment (neurons, macroglia and blood vessels). In a healthy brain, microglia direct the immune response to brain damage and play an important role in

2108-408: The brain and spinal cord. The glia to neuron-ratio varies from one part of the brain to another. The glia to neuron-ratio in the cerebral cortex is 3.72 (60.84 billion glia (72%); 16.34 billion neurons), while that of the cerebellum is only 0.23 (16.04 billion glia; 69.03 billion neurons). The ratio in the cerebral cortex gray matter is 1.48, with 3.76 for the gray and white matter combined. The ratio of

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2176-502: The case of an electrical synapse through a gap junction ); 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, which influence another (postsynaptic) neuron. The postsynaptic neuron may receive inputs from many additional neurons, both excitatory and inhibitory. The excitatory and inhibitory influences are summed, and if

2244-482: The central nervous system arise from three types of neural stem and progenitor cells: neuroepithelial cells, radial glial cells and basal progenitors, which go through three main divisions: symmetric proliferative division; asymmetric neurogenic division; and symmetric neurogenic division. Out of all the three cell types, neuroepithelial cells that pass through neurogenic divisions have a much more extended cell cycle than those that go through proliferative divisions, such as

2312-491: The developing and adult mammalian brain. DNA cytosine methylation is catalyzed by DNA methyltransferases (DNMTs) . Methylcytosine demethylation is catalyzed in several stages by TET enzymes that carry out oxidative reactions (e.g. 5-methylcytosine to 5-hydroxymethylcytosine ) and enzymes of the DNA base excision repair (BER) pathway. Neurogenesis can be a complex process in some mammals. In rodents for example, neurons in

2380-550: The embryonic ventricular zone , which lies adjacent to the central fluid-filled cavity ( ventricular system ) of the neural tube . Following RGC proliferation, neurogenesis involves a final cell division of the parent RGC, which produces one of two possible outcomes. First, this may generate a subclass of neuronal progenitors called intermediate neuronal precursors (INP)s, which will divide one or more times to produce neurons. Alternatively, daughter neurons may be produced directly. Neurons do not immediately form neural circuits through

2448-414: The external chemical environment. Like astrocytes, they are interconnected by gap junctions and respond to ATP by elevating the intracellular concentration of calcium ions. They are highly sensitive to injury and inflammation and appear to contribute to pathological states, such as chronic pain . Are found in the intrinsic ganglia of the digestive system . Glia cells are thought to have many roles in

2516-482: The first investigators of the nervous system, glial cells had been considered to be merely "glue" that held neurons together until the mid-20th century. Glia were first described in 1856 by the pathologist Rudolf Virchow in a comment to his 1846 publication on connective tissue. A more detailed description of glial cells was provided in the 1858 book 'Cellular Pathology' by the same author. When markers for different types of cells were analyzed, Albert Einstein's brain

2584-497: The growth of axons and dendrites. Instead, newborn neurons must first migrate long distances to their final destinations, maturing and finally generating neural circuitry. For example, neurons born in the ventricular zone migrate radially to the cortical plate , which is where neurons accumulate to form the cerebral cortex . Thus, the generation of neurons occurs in a specific tissue compartment or 'neurogenic niche' occupied by their parent stem cells. The rate of neurogenesis and

2652-415: The inflammation that accompanies the damage. Many diseases and disorders are associated with deficient microglia, such as Alzheimer's disease , Parkinson's disease and ALS . Pituicytes from the posterior pituitary are glial cells with characteristics in common to astrocytes. Tanycytes in the median eminence of the hypothalamus are a type of ependymal cell that descend from radial glia and line

2720-558: The mammalian brain unfolds, neural progenitor and stem cells switch from proliferative divisions to differentiative divisions . This progression leads to the generation of neurons and glia that populate cortical layers . Epigenetic modifications play a key role in regulating gene expression in the cellular differentiation of neural stem cells . Epigenetic modifications include DNA cytosine methylation to form 5-methylcytosine and 5-methylcytosine demethylation . These modifications are critical for cell fate determination in

2788-543: The medulla cortex region of their optic lobes. These organisms can represent a model for the genetic analysis of adult neurogenesis and brain regeneration. There has been research that discuss how the study of “damage-responsive progenitor cells” in Drosophila can help to identify regenerative neurogenesis and how to find new ways to increase brain rebuilding. Recently, a study was made to show how “low-level adult neurogenesis” has been identified in Drosophila, specifically in

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2856-463: The medulla cortex region, in which neural precursors could increase the production of new neurons, making neurogenesis occur. In Drosophila, Notch signaling was first described, controlling a cell-to-cell signaling process called lateral inhibition , in which neurons are selectively generated from epithelial cells . In some vertebrates, regenerative neurogenesis has also been shown to occur. An in vitro and in vivo study found that DMT present in

2924-932: The messenger molecule IP3 to diffuse from one astrocyte to another. IP3 activates calcium channels on cellular organelles , releasing calcium into the cytoplasm . This calcium may stimulate the production of more IP3 and cause release of ATP through channels in the membrane made of pannexins . The net effect is a calcium wave that propagates from cell to cell. Extracellular release of ATP, and consequent activation of purinergic receptors on other astrocytes, may also mediate calcium waves in some cases. In general, there are two types of astrocytes, protoplasmic and fibrous, similar in function but distinct in morphology and distribution. Protoplasmic astrocytes have short, thick, highly branched processes and are typically found in gray matter . Fibrous astrocytes have long, thin, less-branched processes and are more commonly found in white matter . It has recently been shown that astrocyte activity

2992-422: The net effect is inhibitory, the neuron will be less likely to "fire" (i.e., generate an action potential), and if the net effect is excitatory, the neuron will be more likely to fire. How likely a neuron is to fire depends on how far its membrane potential is from the threshold potential , the voltage at which an action potential is triggered because enough voltage-dependent sodium channels are activated so that

3060-425: The net inward sodium current exceeds all outward currents. 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 (traditionally at the axon hillock ), it will propagate along

3128-423: The neural crest. These PNS glia include Schwann cells in nerves and satellite glial cells in ganglia. Glia retain the ability to undergo cell divisions in adulthood, whereas most neurons cannot. The view is based on the general inability of the mature nervous system to replace neurons after an injury, such as a stroke or trauma, where very often there is a substantial proliferation of glia, or gliosis , near or at

3196-408: The neuron gets as many inhibitory as excitatory impulses, the inhibition cancels out the excitation and the nerve impulse will stop there. Action potential generation is proportionate to the probability and pattern of neurotransmitter release, and to postsynaptic receptor sensitization. Spatial summation means that the effects of impulses received at different places on the neuron add up, so that

3264-464: The neuron may fire when such impulses are received simultaneously, even if each impulse on its own would not be sufficient to cause firing. Temporal summation means that the effects of impulses received at the same place can add up if the impulses are received in close temporal succession. Thus the neuron may fire when multiple impulses are received, even if each impulse on its own would not be sufficient to cause firing. Neurotransmission implies both

3332-544: The neurons of the CNS varies widely across mammals, and brain neurogenesis is not always complete by the time of birth. For example, mice undergo cortical neurogenesis from about embryonic day (post-conceptional day) (E)11 to E17, and are born at about E19.5. Ferrets are born at E42, although their period of cortical neurogenesis does not end until a few days after birth. In contrast, neurogenesis in humans generally begins around gestational week (GW) 10 and ends around GW 25 with birth about GW 38–40. As embryonic development of

3400-442: The number of available postsynaptic receptors for the neurotransmitter to bind to, and the subsequent removal or deactivation of the neurotransmitter by enzymes or presynaptic reuptake. In response to a threshold action potential or graded electrical potential , a neurotransmitter is released at the presynaptic terminal . The released neurotransmitter may then move across the synapse to be detected by and bind with receptors in

3468-401: The number of glial cells in the brain is correlated with the intelligence of a species. Moreover, evidences are demonstrating the active role of glia, in particular astroglia, in cognitive processes like learning and memory. Neurotransmission This is an accepted version of this page Neurotransmission (Latin: transmissio "passage, crossing" from transmittere "send, let through")

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3536-435: The onset of neurogenesis . Their differentiation abilities are more restricted than those of neuroepithelial cells. In the developing nervous system, radial glia function both as neuronal progenitors and as a scaffold upon which newborn neurons migrate. In the mature brain, the cerebellum and retina retain characteristic radial glial cells. In the cerebellum, these are Bergmann glia , which regulate synaptic plasticity . In

3604-544: The postsynaptic neuron. Binding of neurotransmitters may influence the postsynaptic neuron in either an inhibitory or excitatory way. The binding of neurotransmitters to receptors in the postsynaptic neuron can trigger either short term changes, such as changes in the membrane potential called postsynaptic potentials , or longer term changes by the activation of signaling cascades . Neurons form complex biological neural networks through which nerve impulses (action potentials) travel. Neurons do not touch each other (except in

3672-461: The preservation and consolidation of memories . Glia were discovered in 1856, by the pathologist Rudolf Virchow in his search for a "connective tissue" in the brain. The term derives from Greek γλία and γλοία "glue" ( English: / ˈ ɡ l iː ə / or / ˈ ɡ l aɪ ə / ), and suggests the original impression that they were the glue of the nervous system . Derived from ectodermal tissue. The most abundant type of macroglial cell in

3740-453: The process by which nervous system cells, the neurons , are produced by neural stem cells (NSCs). This occurs in all species of animals except the porifera (sponges) and placozoans . Types of NSCs include neuroepithelial cells (NECs), radial glial cells (RGCs), basal progenitors (BPs), intermediate neuronal precursors (INPs), subventricular zone astrocytes , and subgranular zone radial astrocytes , among others. Neurogenesis

3808-496: The radial glial cells and basal progenitors. In the human, adult neurogenesis has been shown to occur at low levels compared with development, and in only three regions of the brain: the adult subventricular zone (SVZ) of the lateral ventricles , the amygdala and the dentate gyrus of the hippocampus . In many mammals, including rodents, the olfactory bulb is a brain region containing cells that detect smell , featuring integration of adult-born neurons, which migrate from

3876-404: The rate of neurogenesis within the hippocampus of rodents. Some evidence indicates postnatal neurogenesis in the human hippocampus decreases sharply in newborns for the first year or two after birth, dropping to "undetectable levels in adults." Neurogenesis has been best characterized in model organisms such as the fruit fly Drosophila melanogaster . Neurogenesis in these organisms occur in

3944-505: The ratio of glia to neurons increase through evolution, but so does the size of the glia. Astroglial cells in human brains have a volume 27 times greater than in mouse brains. These important scientific findings may begin to shift the neurocentric perspective into a more holistic view of the brain which encompasses the glial cells as well. For the majority of the twentieth century, scientists had disregarded glial cells as mere physical scaffolds for neurons. Recent publications have proposed that

4012-549: The regeneration of damaged fibers. Astrocytes are crucial participants in the tripartite synapse . They have several crucial functions, including clearance of neurotransmitters from within the synaptic cleft , which aids in distinguishing between separate action potentials and prevents toxic build-up of certain neurotransmitters such as glutamate , which would otherwise lead to excitotoxicity . Furthermore, astrocytes release gliotransmitters such as glutamate, ATP, and D-serine in response to stimulation. While glial cells in

4080-511: The result of physical damage to the CNS. Generally, when damage occurs to the CNS, glial cells cause apoptosis among the surrounding cellular bodies. Then, there is a large amount of microglial activity, which results in inflammation, and, finally, there is a heavy release of growth inhibiting molecules. Although glial cells and neurons were probably first observed at the same time in the early 19th century, unlike neurons whose morphological and physiological properties were directly observable for

4148-575: The retina, the radial Müller cell is the glial cell that spans the thickness of the retina and, in addition to astroglial cells, participates in a bidirectional communication with neurons. Similar in function to oligodendrocytes, Schwann cells provide myelination to axons in the peripheral nervous system (PNS). They also have phagocytotic activity and clear cellular debris that allows for regrowth of PNS neurons. Satellite glial cells are small cells that surround neurons in sensory, sympathetic , and parasympathetic ganglia. These cells help regulate

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4216-470: The same time, the other being a cotransmitter, in order to provide the stabilizing negative feedback required for meaningful encoding, in the absence of inhibitory interneurons . Examples include: Noradrenaline and ATP are sympathetic co-transmitters. It is found that the endocannabinoid anadamide and the cannabinoid WIN 55,212-2 can modify the overall response to sympathetic nerve stimulation, and indicate that prejunctional CB1 receptors mediate

4284-430: The site of damage. However, detailed studies have found no evidence that 'mature' glia, such as astrocytes or oligodendrocytes , retain mitotic capacity. Only the resident oligodendrocyte precursor cells seem to keep this ability once the nervous system matures. Glial cells are known to be capable of mitosis . By contrast, scientific understanding of whether neurons are permanently post-mitotic , or capable of mitosis,

4352-844: The synaptic vesicles transiently dock and fuse at the base of specialized 10–15 nm cup-shaped lipoprotein structures at the presynaptic membrane called porosomes . The neuronal porosome proteome has been solved, providing the molecular architecture and the complete composition of the machinery. Recent studies in a myriad of systems have shown that most, if not all, neurons release several different chemical messengers. Cotransmission allows for more complex effects at postsynaptic receptors , and thus allows for more complex communication to occur between neurons. In modern neuroscience, neurons are often classified by their cotransmitter. For example, striatal "GABAergic neurons" utilize opioid peptides or substance P as their primary cotransmitter. Some neurons can release at least two neurotransmitters at

4420-515: The type of neuron generated (broadly, excitatory or inhibitory) are principally determined by molecular and genetic factors. These factors notably include the Notch signaling pathway , and many genes have been linked to Notch pathway regulation . The genes and mechanisms involved in regulating neurogenesis are the subject of intensive research in academic, pharmaceutical , and government settings worldwide. The amount of time required to generate all

4488-493: The usefulness of this feature, and even claim it can "exacerbate" the disease. In addition to affecting the potential repair of neurons in Alzheimer's disease, scarring and inflammation from glial cells have been further implicated in the degeneration of neurons caused by amyotrophic lateral sclerosis . In addition to neurodegenerative diseases, a wide range of harmful exposure, such as hypoxia , or physical trauma, can lead to

4556-432: The vesicle. The second two involve the full fusion of the vesicle with the membrane, followed by recycling, or recycling into the endosome. Vesicular fusion is driven largely by the concentration of calcium in micro domains located near calcium channels, allowing for only microseconds of neurotransmitter release, while returning to normal calcium concentration takes a couple of hundred of microseconds. The vesicle exocytosis

4624-464: Was discovered to contain significantly more glia than normal brains in the left angular gyrus , an area thought to be responsible for mathematical processing and language. However, out of the total of 28 statistical comparisons between Einstein's brain and the control brains, finding one statistically significant result is not surprising, and the claim that Einstein's brain is different is not scientific (c.f. multiple comparisons problem ). Not only does

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