Myelin is a lipid-rich substance that surrounds nerve cell axons to insulate them and increase the rate at which electrical impulses are passed along the axon. The myelinated axon can be likened to an electrical wire with insulating material around it. However, unlike the plastic covering on an electrical wire, myelin does not form a single long sheath over the entire length of the axon. Rather, each myelin sheath insulates the axon over a single long section and, in general, each axon comprises multiple long myelinated sections separated from each other by short gaps called nodes of Ranvier. Myelin is formed in the central nervous system by glial cells called oligodendrocytes and in the peripheral nervous system by glial cells called Schwann cells. In the CNS, axons carry electrical signals from one nerve cell body to another. In the PNS, axons carry signals from sensory organs such as the skin; each myelin sheath is formed by the concentric wrapping of an oligodendrocyte or Schwann cell process around the axon.
Myelin reduces the capacitance of the axonal membrane. On a molecular level, in the internodes it increases the distance between extracellular and intracellular ions, reducing the accumulation of charges; the discontinuous structure of the myelin sheath results in saltatory conduction, whereby the action potential "jumps" from one node of Ranvier, over a long myelinated stretch of the axon called the internode, before "recharging" at the next node of Ranvier, so on, until it reaches the axon terminal. Nodes of Ranvier are the short unmyelinated regions of the axon between adjacent long myelinated internodes. Once it reaches the axon terminal, this electrical signal provokes the release of a chemical message or neurotransmitter that binds to receptors on the adjacent post-synaptic cell at specialised regions called synapses; this "insulating" role for myelin is essential for normal motor function, sensory function and cognition, as demonstrated by the consequences of disorders that affect it, such as the genetically determined leukodystrophies.
Due to its high prevalence, multiple sclerosis, which affects the central nervous system, is the best known disorder of myelin. The process of generating myelin is called myelination or myelinogenesis. In the CNS, cells called oligodendrocyte precursor cells differentiate into mature oligodendrocytes, which form myelin. In humans, myelination begins early in the 3rd trimester, although only little myelin is present in either the CNS or the PNS at the time of birth. During infancy, myelination progresses with increasing numbers of axons acquiring myelin sheaths; this corresponds with the development of cognitive and motor skills, including language comprehension, speech acquisition and walking. Myelination continues through adolescence and early adulthood and although complete at this time, myelin sheaths can be added in grey matter regions such as the cerebral cortex, throughout life. Myelin is considered a defining characteristic of the jawed vertebrates, though axons are ensheathed by a type of cell, called glial cells, in invertebrates.
These glial wraps are quite different from vertebrate compact myelin, formed, as indicated above, by concentric wrapping of the myelinating cell process multiple times around the axon. Myelin was first described in 1854 by Rudolf Virchow, although it was over a century following the development of electron microscopy, that its glial cell origin and its ultrastructure became apparent. In vertebrates, not all axons are myelinated. For example, in the PNS, a large proportion of axons are unmyelinated. Instead, they are ensheathed by non-myelinating Schwann cells known as Remak SCs and arranged in Remak bundles. In the CNS, non-myelinated axons intermingle with myelinated ones and are entwined, at least by the processes of another type of glial cell called the astrocyte. CNS myelin differs in composition and configuration from PNS myelin, but both perform the same "insulating" function. Being rich in lipid, myelin appears white, hence the name given to the "white matter" of the CNS. Both CNS white matter tracts and PNS nerves each comprise thousands to millions of axons aligned in parallel.
Blood vessels provide the route for oxygen and energy substrates such as glucose to reach these fibre tracts, which contain other cell types including astrocytes and microglia in the CNS and macrophages in the PNS. In terms of total mass, myelin comprises 40% water. Protein content includes myelin basic protein, abundant in the CNS where it plays a critical, non-redundant role in formation of compact myelin. In the PNS, myelin protein zero has a similar rol
Established in 1976, Fundação Dom Cabral is a world-class Brazilian business school that develops strategic thinking skills of executives and public-sector managers. FDC, a nonprofit institution, was created out of the Extension Center at the Pontifical Catholic University of Minas Gerais. 40,000 executives from midsize and large companies attend FDC programs every year – in the cities of Nova Lima, Belo Horizonte, São Paulo, Rio de Janeiro. FDC has strategic alliances with foreign teaching institutions such as INSEAD and Skema Business School in France and the Kellogg School of Management at Northwestern University in the U. S. FDC has cooperative partnerships with schools in Brazil, Colombia, China, Mexico, Portugal, Russia and United Kingdom. For the 13th consecutive year, the Financial Times has ranked Fundação Dom Cabral the best business school in Latin America. 1976 - Fundação Dom Cabral was founded. 1989 – Creation of the first partnership program: CTE – Executive Technology Center 1990 – Alliance with INSEAD to develop open enrollment programs for senior executives working in Brazil 1992 – Creation of PAEX – Partners for Excellence, a partnership program for middle-sized companies 1993 – Alliance with Kellogg School of Management - Northwestern University to develop open enrollment program for leaders of companies operating in Brazil 1996 – Launching of the MBA Empresarial an executive MBA program in consortium 1999 – Creation of PDA – a partnership for the development of family business shareholders 2001 – Inauguration of the FDC Aloysio Farias Campus located in the city of Nova Lima, 30 km south of Belo Horizonte 2002 – Alliance with Sauder School of Business to develop programs for high potential managers and programs on specific subjects including a program in China 2004 – Fundação Dom Cabral joined the UN Global Compact, pledging to insert its principles into the institution’s decisions and to collaborate in spreading business practices expressing the values of sustainable development.
2005 - Accreditation of the MBA programs by AMBA. 2007 - Received the EQUIS accreditation. 2012 - Signed a partnership with Hult International Business School to become host of their global campus rotation program. 2015 - Signed a partnership with Skema Business School to become host of Skema's Grande École program Official website
Commercial Valuers and Surveyors provides business rent and rates services to occupiers of commercial property in the United Kingdom. CVS has a team of business rates surveyors who are experienced at lodging business rates appeals at the Valuation Office Agency; the firm is headquartered in Manchester, has offices in Old Trafford, Greater Manchester, City of London and Bristol. The company was founded in 1999 and is directed by Mark Rigby, the current CEO; the firm has a national network of chartered surveyors. CVS’ principle areas of practice include advice and commentary on commercial property valuation, property tax and services. ’Highly commended’ for Estates Gazette’s National Property Advisor of the Year 2014 Ranked in the top 20 firms in the Property Week Agency Survey, 2014'Finalist' for Estates Gazette's National Advisor of the Year 2015'Finalist' for Property Week's'Professional Agency Team of the Year' at the 2016 Property Awards'Finalist' for Estates Gazette's Specialist Adviser of the Year 2017 The company operates from the following offices: Oakland House, Talbot Road, Manchester Woolgate Exchange, 25 Basinghall Street, London Bull Wharf, Redcliff Street, Bristol Official website