Myelin dielectric (electrically insulating) material, evidence of evolution, or design ? elshamah.heavenforum.org/t1859-insulated-cables#3108 iaincarstairs.wordpress/2013/03/25/as-smart-as-molecules/ en.wikipedia.org/wiki/Myelin Myelin is a dielectric (electrically insulating) material that forms a layer, the myelin sheath, usually around only the axon of a neuron. It is essential for the proper functioning of the nervous system. Since its essential , how could it have evolved, if the nervous system probably would not function properly without it ? Function The main purpose of a myelin layer (or sheath) 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, they hop or propagate by saltation. How did evolution forsee and know that myelin layer would increase the impulse speed, in order to evolve this function ? there would be no function and desease, unless the function is fully in place Demyelination results in diverse symptoms determined by the functions of the affected neurons. It disrupts signals between the brain and other parts of the body; symptoms differ from patient to patient, and have different presentations upon clinical observation and in laboratory studies. Demyelination Typical symptoms include: blurriness in the central visual field that affects only one eye, may be accompanied by pain upon eye movement double vision loss of vision/hearing odd sensation in legs, arms, chest, or face, such as tingling or numbness (neuropathy) weakness of arms or legs cognitive disruption, including speech impairment and memory loss heat sensitivity (symptoms worsen or reappear upon exposure to heat, such as a hot shower) loss of dexterity difficulty coordinating movement or balance disorder difficulty controlling bowel movements or urination fatigue Saltatory conduction (from the Latin saltare, to hop or leap) is the propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials. Absent nodes (uninsulated sections) separated by the myelin sheaths, an electrical potential spike must be rebuilt many more times along the axonal membrane. Thus the conduction we describe here is propagation of ion exchanges across a nerve cell membrane, and is not similar to conduction of electrons in an electrical circuit. Mechanism In order for a signal to travel along the axon of a nerve cell, a charge must build up across the axonal membrane. This spike in voltage is what it termed an Action Potential (AP). Creation of APs must be repeated many times at structures along the axon known as ion gates.[1] However with myelin sheaths insulating the axon an AP is observed to jump to the next ion gate which occurs at a neighboring Ranvier node. Thus in myelinated axons, action potentials can hop along the axon, by which process the signal travels faster by skipping around the insulated sections. (The action potential only moves in one direction, because the sodium channels at the previous node of Ranvier are inactivated, and cannot regenerate another action potential, even when depolarized. The charge will passively depolarize the adjacent node of Ranvier to threshold, triggering an action potential in this region and subsequently depolarizing the next node, and so on.) How could evolution possibly have found out about this behavior, in order to evolve the function ? Since evolution has no forsight and knowledge, it seems not possible to me that it could evolve the function . Glial Cells apologeticspress.org/apcontent.aspx?category=12&article=1697 Nerve cells are surrounded by a supporting network composed of glial cells (from the Greek glia, meaning glue). Glial cells are present in small numbers before birth, but the majority of these cells are derived after birth. There are 10-50 times more glial cells than neurons (Kandel, et al., 1991, p. 22). If nerve cells serve as the active signaling cells, glial cells are the glue that holds everything together and helps maintain proper function of the entire system. For instance, the mylein sheath not only insulates the neuron, but also helps to speed up transmission of the nerve signal. Within the nervous system, myelin is produced by specialized glial cells known as Schwann cells which surround the axon. Schwann cells are believed to serve as nutritive, supportive, and service facilities for neurons. Spaced along the Schwann cells are gaps known as the node of Ranvier (named after neuroanatomist Louis Antoine Ranvier) which help to speed up signal transduction as well as generate nerve signals. These gaps are not random, but rather are deliberately situated to help the brain communicate to distant regions of the body (e.g., toes) in just a few thousandths of a second. Once again, an honest examination would cause one to conclude that these gaps are purposefully arranged. In an abstract titled: “Evolution of Myelin Proteins,” Gould, et al. observed: The myelinated nervous system arose in a common ancestor of all modern-day gnathostomes (jawed animals). Modern-day agnathans (jawless animals, i.e., lamprey and hagfish) have nervous systems that contain large axons surrounded by glial cells, but no mylein. In order for myelination to evolve, both neurons and axons had to simultaneously develop appropriate communication pathways . Pathways from large axons were designed not only to attract glial cells, but also to induce them to form myelin internodes of appropriate size for the axon. The associating glial cells in turn need to signal neurons/axons to target ion channels and other proteins to specialized regions called nodes of Ranvier. The accumulation of ion channels at nodes of Ranvier is an essential feature of rapid saltatory nerve conduction (2004, p. 168, parenthetical items in orig., emp. added). Evolutionists have yet to demonstrate a transitional glial cell. Gould, et al. recognize that the development of myelin would require both neurons and axons to “simultaneously develop appropriate communication pathways.” Has this simultaneous development ever been recorded in nature? Are myelin and glial cells essential to the human nervous system? Just ask someone suffering from multiple sclerosis (MS). This condition is suspected to be caused by a viral infection where myelin in the central nervous system is attacked in an autoimmune response. A second group of demyelinating diseases are degenerative diseases identified as leukodystrophies. In 2001, D.R. Cotter and colleagues presented a paper titled “Glial Cell Abnormalities in Major Psychiatric Disorders: The Evidence and Implications” in Brain Research Bulletin, acknowledging that glial cell loss may be responsible for many different pathological changes and disorders (p. 585). So, are myelin and glial cells a critical component of the human nervous system? Yes! Can evolution explain their existence? No. Francis Crick once noted: “Biologists must constantly keep in mind that what they see was not designed, but rather evolved” (1990, p. 138). Crick realized that a purposeful arrangement pointed toward design, and in order to negate any notion of a designer, biologists constantly need to ignore the obvious—the elephant of intelligent design.
Posted on: Tue, 12 Aug 2014 02:27:47 +0000
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