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The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. The brain is located in the head, usually close to the sensory organs for senses such as vision. The brain is the most complex organ in a vertebrate's body. In a human, the cerebral cortex contains approximately 14–16 billion neurons, and the estimated number of neurons in the cerebellum is 55–70 billion. Each neuron is connected by synapses to several thousand other neurons. These neurons communicate with one another by means of long protoplasmic fibers called axons, which carry trains of signal pulses called action potentials to distant parts of the brain or body targeting specific recipient cells.
Dopamine is an organic chemical of the catecholamine and phenethylamine families. It functions both as a hormone and a neurotransmitter, and plays several important roles in the brain and body. It is an amine synthesized by removing a carboxyl group from a molecule of its precursor chemical L-DOPA, which is synthesized in the brain and kidneys. Dopamine is also synthesized in plants and most animals. In the brain, dopamine functions as a neurotransmitter—a chemical released by neurons to send signals to other nerve cells. The brain includes several distinct dopamine pathways, one of which plays a major role in the motivational component of reward-motivated behavior. The anticipation of most types of rewards increases the level of dopamine in the brain, and many addictive drugs increase dopamine release or block its reuptake into neurons following release. Other brain dopamine pathways are involved in motor control and in controlling the release of various hormones. These pathways and cell groups form a dopamine system which is neuromodulatory.
The hippocampus is a major component of the brains of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory, and in spatial memory that enables navigation. The hippocampus is located under the cerebral cortex (allocortical) and in primates in the medial temporal lobe. It contains two main interlocking parts: the hippocampus proper and the dentate gyrus.
The blood–brain barrier (BBB) is a highly selective semipermeable border that separates the circulating blood from the brain and extracellular fluid in the central nervous system (CNS). The blood–brain barrier is formed by endothelial cells of the capillary wall, astrocyte end-feet ensheathing the capillary, and pericytes embedded in the capillary basement membrane. This system allows the passage of some molecules by passive diffusion, as well as the selective transport of molecules such as glucose, water and amino acids that are crucial to neural function.
gamma-Aminobutyric acid, or γ-aminobutyric acid, or GABA, is the chief inhibitory neurotransmitter in the developmentally mature mammalian central nervous system. Its principal role is reducing neuronal excitability throughout the nervous system. In humans, GABA is also directly responsible for the regulation of muscle tone.
Glia, also called glial cells or neuroglia, are non-neuronal cells in the central nervous system and the peripheral nervous system. They maintain homeostasis, form myelin, and provide support and protection for neurons. In the central nervous system, glial cells include oligodendrocytes, astrocytes, ependymal cells, and microglia, and in the peripheral nervous system glial cells include Schwann cells and satellite cells. They have four main functions: (1) to surround neurons and hold them in place; (2) to supply nutrients and oxygen to neurons; (3) to insulate one neuron from another; (4) to destroy pathogens and remove dead neurons. They also play a role in neurotransmission and synaptic connections, and in physiological processes like breathing. While glia were thought to outnumber neurons by a ratio of 10:1, a recent study provides evidence for a ratio of less than 1:1.
Glioblastoma, also known as glioblastoma multiforme (GBM), is the most aggressive cancer that begins within the brain. Initially, signs and symptoms of glioblastoma are non-specific. They may include headaches, personality changes, nausea, and symptoms similar to those of a stroke. Worsening of symptoms often is rapid. This may progress to unconsciousness.
Dehydroascorbic acid (DHA) is an oxidized form of ascorbic acid. It is actively imported into the endoplasmic reticulum of cells via glucose transporters. It is trapped therein by reduction back to ascorbate by glutathione and other thiols. The (free) chemical radical semidehydroascorbic acid (SDA) also belongs to the group of oxidized ascorbic acids.
Nuclear receptor TLX also known as NR2E1 is a protein that in humans is encoded by the NR2E1 gene. TLX is a member of the nuclear receptor family of intracellular transcription factors.
Metabotropic glutamate receptor 8 is a protein that in humans is encoded by the GRM8 gene.
Homeobox protein OTX2 is a protein that in humans is encoded by the OTX2 gene.
POU domain, class 3, transcription factor 1 is a protein that in humans is encoded by the POU3F1 gene.
CD8a, is a human gene.
Benzamil or benzyl amiloride is a potent blocker of the ENaC channel and also a sodium-calcium exchange blocker. It is a potent analog of amiloride, and is marketed as the hydrochloride salt. As amiloride, benzamil has been studied as a possible treatment for cystic fibrosis, although with disappointing results.
The Mauthner cells are a pair of big and easily identifiable neurons located in the rhombomere 4 of the hindbrain in fish and amphibians that are responsible for a very fast escape reflex. The cells are also notable for their unusual use of both chemical and electrical synapses.
Noradrenergic cell group A1 is a group of cells in the vicinity of the lateral reticular nucleus of the medullary reticular formation that label for norepinephrine in primates and rodents. They are found in the ventrolateral medulla in conjunction with the adrenergic cell group C1.
Noradrenergic cell group A2 is a group of cells in the vicinity of the dorsal motor nucleus of the vagus nerve in the medulla that label for norepinephrine in primates and rodents.
Noradrenergic cell group A5 is a group of cells in the vicinity of the superior olivary complex in the pontine tegmentum that label for norepinephine in primates, rodents and other mammals.
Dopaminergic cell groups are collections of neurons in the central nervous system that synthesize the neurotransmitter dopamine. In the 1960s, dopamine neurons were first identified and named by Annica Dahlström and sv:Kjell Fuxe, who used histochemical fluorescence. The subsequent discovery of genes encoding enzymes that synthesize dopamine, and transporters that incorporate dopamine into synaptic vesicles or reclaim it after synaptic release, enabled scientists to identify dopaminergic neurons by labeling gene or protein expression that is specific to these neurons.
References
- ↑ Felten DL; Sladek JR Jr. (1983). "Monoamine distribution in primate brain V. Monoaminergic nuclei: anatomy, pathways and local organization". Brain Research Bulletin. 10 (2): 171–284. doi:10.1016/0361-9230(83)90045-x. PMID 6839182.
- ↑ German DC; Bowden DM (1975). "Locus ceruleus in rhesus monkey (Macaca mulatta): a combined histochemical fluorescence, Nissl and silver study". J Comp Neurol. 161: 19–29. doi:10.1002/cne.901610104. PMID 48520.
