A molecule inside or on the surface of a cell that binds to a specific substance and causes a specific effect in the cell. Schwann Cells. Schwann cells function to support neurons in the peripheral nervous system. Schwann cells wrap around axons to form the myelin sheath.
Which cells form myelin in the spinal cord Quizlet?
In the central nervous system (CNS) — the brain and spinal cord — cells called oligodendrocytes wrap their branch-like extensions around axons to create a myelin sheath. In the nerves outside of the spinal cord, Schwann cells produce myelin. Click to see full answer. Likewise, which cells form myelin in the spinal cord quizlet?
What is myelin myelin in vertebrates?
Myelin is considered a defining characteristic of the jawed vertebrates ( gnathostomes ), though axons are ensheathed by a type of cell, called glial cells, in invertebrates.
Where is myelin sheath found in the nervous system?
In the central nervous system (CNS) — the brain and spinal cord — cells called oligodendrocytes wrap their branch-like extensions around axons to create a myelin sheath. In the nerves outside of the spinal cord, Schwann cells produce myelin. Click to see full answer.
What is the function of myelin in nerve cells?
Myelin insulates nerve cell axons to increase the speed at which information (encoded as an electrical signal) travels from one nerve cell body to another (as in the CNS) or, for example, from a nerve cell body to a muscle (as in the PNS).
Which cells form myelin in the spinal cord quizlet?
Oligodendrocytes do this by creating the myelin sheath, which is 80% lipid and 20% protein. are a type of glial cell that are the resident macrophages of the brain and spinal cord, and thus act as the first and main form of active immune defense in the central nervous system (CNS).
Which cells produce myelin in the brain and spinal cord quizlet?
Schwann cells produce the myelin sheath that wraps around a single axon of the neurons in the PNS. They also assist in regeneration of the PNS axons.
Which cells produce myelin quizlet?
Two types of neuroglia produce myelin sheaths: Schwann cells (in the PNS) and oligodendrocytes (in the CNS). In the PNS, Schwann cells begin to form myelin sheaths around axons during fetal development.
What cell type forms the myelin sheath in the central nervous system CNS )? Quizlet?
Oligodendrocytes form myelin sheaths in the CNS. One cell can wrap around as many as 60 different axons.
What is myelin in vertebrates?
Myelin is considered a defining characteristic of the jawed vertebrates ( gnathostomes ), 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 later, following the development of electron microscopy, that its glial cell origin and its ultrastructure became apparent.
Where is myelin found?
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. In the CNS, axons carry electrical signals from one nerve cell body to another. In the PNS, axons carry signals to muscles ...
What is the process of myelination?
The process of generating myelin is called myelination or myelinogenesis. In the CNS, cells called oligodendrocyte precursor cells (OPCs; the precursors of oligodendrocytes) 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 rapidly, with increasing numbers of axons acquiring myelin sheaths. This corresponds with the development of cognitive and motor skills, including language comprehension, speech acquisition, crawling and walking. Myelination continues through adolescence and early adulthood and although largely complete at this time, myelin sheaths can be added in grey matter regions such as the cerebral cortex, throughout life.
What is the discontinuous structure of the myelin sheath?
The discontinuous structure of the myelin sheath results in saltatory conduction, where by 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, and so on, until it reaches the axon terminal.
How to repair myelin sheaths?
Research to repair damaged myelin sheaths is ongoing. Techniques include surgically implanting oligodendrocyte precursor cells in the central nervous system and inducing myelin repair with certain antibodies. While results in mice have been encouraging (via stem cell transplantation), whether this technique can be effective in replacing myelin loss in humans is still unknown. Cholinergic treatments, such as acetylcholinesterase inhibitors (AChEIs), may have beneficial effects on myelination, myelin repair, and myelin integrity. Increasing cholinergic stimulation also may act through subtle trophic effects on brain developmental processes and particularly on oligodendrocytes and the lifelong myelination process they support. Increasing oligodendrocyte cholinergic stimulation, AChEIs, and other cholinergic treatments, such as nicotine, possibly could promote myelination during development and myelin repair in older age. Glycogen synthase kinase 3β inhibitors such as lithium chloride have been found to promote myelination in mice with damaged facial nerves. Cholesterol is a necessary nutrient for the myelin sheath, along with vitamin B12.
Why is action potential faster in myelinated neurons than in unmyelinated neurons?
Action potential propagation in myelinated neurons is faster than in unmyelinated neurons because of Saltatory conduction. The main purpose of myelin is to increase the speed at which electrical impulses propagate along the myelinated fiber. In unmyelinated fibers, electrical impulses ( action potentials) travel as continuous waves, but, ...
What is the name of the substance that surrounds nerve cells?
Nervous system. Identifiers. FMA. 62977. Anatomical terminology. Myelin is a lipid -rich (fatty) substance that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can be likened to an electrical wire ...
Overview
Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can be likened to an electrical wire (the axon) with insulating material (myelin) around it. However, unlike the plastic covering on an electrical wire, m…
Development
The process of generating myelin is called myelination or myelinogenesis. In the CNS, oligodendrocyte progenitor cells (OPCs) 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 rapidly, with increasing numbers of axons acquiring myelin sheaths. This corresponds with the d…
Species distribution
Myelin is considered a defining characteristic of the jawed vertebrates (gnathostomes), 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 later, following the develop…
Composition
CNS myelin differs slightly in composition and configuration from PNS myelin, but both perform the same "insulating" function (see above). Being rich in lipid, myelin appears white, hence the name given to the "white matter" of the CNS. Both CNS white matter tracts (e.g. the optic nerve, corticospinal tract and corpus callosum) and PNS nerves (e.g. the sciatic nerve and the auditory nerve, which …
Function
The main purpose of myelin is to increase the speed at which electrical impulses (known as action potentials) propagate along the myelinated fiber. In unmyelinated fibers, action potentials travel as continuous waves, but, in myelinated fibers, they "hop" or propagate by saltatory conduction. The latter is markedly faster than the former, at least for axons over a certain diameter. Myelin decreases capacitance and increases electrical resistance across the axonal membrane (the axole…
Clinical significance
Demyelination is the loss of the myelin sheath insulating the nerves, and is the hallmark of some neurodegenerative autoimmune diseases, including multiple sclerosis, acute disseminated encephalomyelitis, neuromyelitis optica, transverse myelitis, chronic inflammatory demyelinating polyneuropathy, Guillain–Barré syndrome, central pontine myelinosis, inherited demyelinating diseases such as leukodystrophy, and Charcot–Marie–Tooth disease. Sufferers of pernicious an…
Invertebrate myelin
Functionally equivalent myelin-like sheaths are found in several invertebrate taxa including oligochaetes, penaeids, palaemonids, and calanoids. These myelin-like sheaths share several structural features with the sheaths found in vertebrates including multiplicity of membranes, condensation of membrane, and nodes. However, the nodes in vertebrates are annular; i.e. they encircle the axon. In contrast, nodes found in the sheaths of invertebrates are either annular or f…
See also
• Lesional demyelinations of the central nervous system
• Myelin-associated glycoprotein
• Myelin incisure
• The Myelin Project, project to regenerate myelin