why some axons are surrounded by a myelin sheath?
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Much like the insulation around the wires in electrical systems, glial cells form a membraneous sheath surrounding axons called myelin, thereby insulating the axon. This myelination, as it is called, can greatly increase the speed of signals transmitted between neurons (known as action potentials).
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Myelin is formed in the central nervous system (CNS; brain, spinal cord and optic nerve) by glial cells called oligodendrocytes and in the peripheral nervous system (PNS) by glial cells called Schwann cells.
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Nerve cells have branched connections at each end. These join to other nerve cells, allowing them to pass messages around the body. They have a fatty (myelin) sheath that surrounds them. The fatty sheath increases the speed at which the message can travel.
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Numerous dendrons and dendrites provide a large surface area for connecting with other neurones, and carry nerve impulses towards the cell body. A single long axon carries the nerve impulse away from the cell body.
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The glial cells that produce myelin in the central nervous system are called oligodendrocytes. In the peripheral nervous system, the myelin producing cells are called Schwann cells. Each oligodendrocyte can supply myelin for the axons of several nerve cells and each axon can be supplied by several oligodendrocytes.
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A demyelinating disease is any condition that results in damage to the protective covering (myelin sheath) that surrounds nerve fibers in your brain, optic nerves and spinal cord. When the myelin sheath is damaged, nerve impulses slow or even stop, causing neurological problems.
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Schwann cells make myelin in the peripheral nervous system (PNS: nerves) and oligodendrocytes in the central nervous system (CNS: brain and spinal cord). ... No; they can be either myelinated or unmyelinated. Myelinated axons are ensheathed along their entire length.
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Are all axons covered with myelin? No; they can be either myelinated or unmyelinated. Myelinated axons are ensheathed along their entire length. The axon caliber (diameter) in mammalian PNS ranges from 0.1 μm to 20 μm, with unmyelinated axons being less than 2 μm and myelinated axons being more than 1–2 μm in diameter.
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The myelinating glial cells; oligodendrocytes in the central nervous system (CNS), and Schwann cells in the peripheral nervous system (PNS), are wrapped around the axon, leaving the axolemma relatively uncovered at the regularly spaced nodes of Ranvier.
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Nerves. Nerves are bundles of axons in the peripheral nervous system (PNS) that act as information highways to carry signals between the brain and spinal cord and the rest of the body. Each axon is wrapped in a connective tissue sheath called the endoneurium.
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An axon, or nerve fiber, is a long slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma. Axons are in effect the primary transmission lines of the nervous system, and as bundles they help make up nerves.
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Most axons are covered with a fatty material called________________ , which insulates the fibers and increases the speed of neurotransmission.
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An axon typically develops side branches called axon collaterals, so that one neuron can send information to several others. These collaterals, just like the roots of a tree, split into smaller extensions called terminal branches. Each of these has a synaptic terminal on the tip.
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After peripheral nerve injury, axons readily regenerate. The distal portion of the axon, which is disconnected from the cell body, undergoes Wallerian degeneration. This active process results in fragmentation and disintegration of the axon. Debris is removed by glial cells, predominantly macrophages.
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Axons tend to be thinner than dendrites, which is another reason they can be more difficult to track down. If you are unsure whether or not you are looking at an axon, look at the thickness of the other neurites around it to compare. An axon should almost always be thinner.
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Many axons are surrounded by a segmented, white, fatty substance called myelin or the myelin sheath. ... In the CNS, oligodendrocytes produce myelin, but there is no neurilemma, which is why fibers within the CNS do not regenerate.
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Neuron. The functional unit of the nervous system is the neuron, a cell specialized to receive and transmit impulses. ... The axons of the peripheral nerves are enclosed in a fatty (myelin) sheath formed from specialized cells called Schwann cells.