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Unmyelinated
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, myelin does not form a single long sheath over the entire length of the axon. Rather, myelin sheaths the nerve in segments: in general, each axon is encased with multiple long myelinated sections with short gaps in between called nodes of Ranvier. 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 and glands or from sensor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Action Potential
An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and in some plant cells. Certain endocrine cells such as pancreatic beta cells, and certain cells of the anterior pituitary gland are also excitable cells. In neurons, action potentials play a central role in cell-cell communication by providing for—or with regard to saltatory conduction, assisting—the propagation of signals along the neuron's axon toward synaptic boutons situated at the ends of an axon; these signals can then connect with other neurons at synapses, or to motor cells or glands. In other types of cells, their main function is to activate intracellular processes. In muscle cells, for example, an action potential is the first step in the chain of events l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Axons
An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action potentials away from the Soma (biology), nerve cell body. The function of the axon is to transmit information to different neurons, muscles, and glands. In certain sensory neurons (pseudounipolar neurons), such as those for touch and warmth, the axons are called afferent nerve fibers and the electrical impulse travels along these from the peripheral nervous system, periphery to the cell body and from the cell body to the spinal cord along another branch of the same axon. Axon dysfunction can be the cause of many inherited and acquired neurological disorders that affect both the Peripheral nervous system, peripheral and Central nervous system, central neurons. Nerve fibers are Axon#Cl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Saltatory Conduction
In neuroscience, saltatory conduction () 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. The uninsulated nodes of Ranvier are the only places along the axon where ions are exchanged across the axon membrane, regenerating the action potential between regions of the axon that are insulated by myelin, unlike electrical conduction in a simple circuit. Mechanism Myelinated axons only allow action potentials to occur at the unmyelinated nodes of Ranvier that occur between the myelinated internodes. It is by this restriction that saltatory conduction propagates an action potential along the axon of a neuron at rates significantly higher than would be possible in unmyelinated axons (150 m/s compared to 0.5 to 10 m/s). As sodium rushes into the node it creates an electrical force which pushes on the ions already inside the axon. This rapid conduction of electrical ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Node Of Ranvier
In neuroscience and anatomy, nodes of Ranvier ( ), also known as myelin-sheath gaps, occur along a myelinated axon where the axolemma is exposed to the extracellular space. Nodes of Ranvier are uninsulated and highly enriched in ion channels, allowing them to participate in the exchange of ions required to regenerate the action potential. Nerve conduction in myelinated axons is referred to as saltatory conduction () due to the manner in which the action potential seems to "jump" from one node to the next along the axon. This results in faster conduction of the action potential. Overview Many vertebrate axons are surrounded by a myelin sheath, allowing rapid and efficient saltatory ("jumping") propagation of action potentials. The contacts between neurons and glial cells display a very high level of spatial and temporal organization in myelinated fibers. The myelinating glial cells - oligodendrocytes in the central nervous system (CNS), and Schwann cells in the peripheral nervou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Grey Matter
Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil (dendrites and unmyelinated axons), glial cells (astrocytes and oligodendrocytes), synapses, and capillaries. Grey matter is distinguished from white matter in that it contains numerous cell bodies and relatively few myelinated axons, while white matter contains relatively few cell bodies and is composed chiefly of long-range myelinated axons. The colour difference arises mainly from the whiteness of myelin. In living tissue, grey matter actually has a very light grey colour with yellowish or pinkish hues, which come from capillary blood vessels and neuronal cell bodies. Structure Grey matter refers to unmyelinated neurons and other cells of the central nervous system. It is present in the brain, brainstem and cerebellum, and present throughout the spinal cord. Grey matter is distributed at the surface of the cerebral hemispheres (cerebral cortex) and of the cerebellu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Myelinogenesis
Myelinogenesis is the formation and development of myelin sheaths in the nervous system, typically initiated in late prenatal neurodevelopment and continuing throughout postnatal development. Myelinogenesis continues throughout the lifespan to support learning and memory via neural circuit plasticity as well as remyelination following injury. Successful myelination of axons increases action potential speed by enabling saltatory conduction, which is essential for timely signal conduction between spatially separate brain regions, as well as provides metabolic support to neurons. Stages Myelin is formed by oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. Therefore, the first stage of myelinogenesis is often defined as the differentiation of oligodendrocyte progenitor cells or Schwann cell progenitors into their mature counterparts, followed by myelin formation around axons. The oligodendrocyte lineage can be further classified into ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oligodendrocyte Progenitor Cells
Oligodendrocyte progenitor cells (OPCs), also known as oligodendrocyte precursor cells, NG2-glia, O2A cells, or polydendrocytes, are a subtype of glia in the central nervous system named for their essential role as precursors to oligodendrocytes. They are typically identified by coexpression of PDGFRA and NG2. OPCs play a critical role in developmental and adult myelinogenesis by giving rise to oligodendrocytes, which then ensheath axons and provide electrical insulation in the form of a myelin sheath, enabling faster action potential propagation and high fidelity transmission without a need for an increase in axonal diameter. The loss or lack of OPCs, and consequent lack of differentiated oligodendrocytes, is associated with a loss of myelination and subsequent impairment of neurological functions. In addition, OPCs express receptors for various neurotransmitters and undergo membrane depolarization when they receive synaptic inputs from neurons. Structure OPCs are glial cells ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Central Nervous System
The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all parts of the bodies of bilaterally symmetric and triploblastic animals—that is, all multicellular animals except sponges and diploblasts. It is a structure composed of nervous tissue positioned along the rostral (nose end) to caudal (tail end) axis of the body and may have an enlarged section at the rostral end which is a brain. Only arthropods, cephalopods and vertebrates have a true brain (precursor structures exist in onychophorans, gastropods and lancelets). The rest of this article exclusively discusses the vertebrate central nervous system, which is radically distinct from all other animals. Overview In vertebrates, the brain and spinal cord are both enclosed in the meninges. The meninges provide a barrier to chemicals dissolv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oligodendrocyte
Oligodendrocytes (), or oligodendroglia, are a type of neuroglia whose main functions are to provide support and insulation to axons in the central nervous system of jawed vertebrates, equivalent to the function performed by Schwann cells in the peripheral nervous system. Oligodendrocytes do this by creating the myelin sheath. A single oligodendrocyte can extend its processes to 50 axons, wrapping approximately 1 μm of myelin sheath around each axon; Schwann cells, on the other hand, can wrap around only one axon. Each oligodendrocyte forms one segment of myelin for several adjacent axons. Oligodendrocytes are found only in the central nervous system, which comprises the brain and spinal cord. These cells were originally thought to have been produced in the ventral neural tube; however, research now shows oligodendrocytes originate from the ventral ventricular zone of the embryonic spinal cord and possibly have some concentrations in the forebrain. They are the last cell ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Peripheral Neuropathies
Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland, or organ function depending on which nerves are affected; in other words, neuropathy affecting motor, sensory, or autonomic nerves result in different symptoms. More than one type of nerve may be affected simultaneously. Peripheral neuropathy may be acute (with sudden onset, rapid progress) or chronic (symptoms begin subtly and progress slowly), and may be reversible or permanent. Common causes include systemic diseases (such as diabetes or leprosy), hyperglycemia-induced glycation, vitamin deficiency, medication (e.g., chemotherapy, or commonly prescribed antibiotics including metronidazole and the fluoroquinolone class of antibiotics (such as ciprofloxacin, levofloxacin, moxifloxacin)), traumatic injury, ischemia, radiation therapy, excessiv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schwann Cell
Schwann cells or neurolemmocytes (named after German physiologist Theodor Schwann) are the principal glia of the peripheral nervous system (PNS). Glial cells function to support neurons and in the PNS, also include satellite cells, olfactory ensheathing cells, enteric glia and glia that reside at sensory nerve endings, such as the Pacinian corpuscle. The two types of Schwann cells are myelinating and nonmyelinating. Myelinating Schwann cells wrap around axons of motor and sensory neurons to form the myelin sheath. The Schwann cell promoter is present in the downstream region of the human dystrophin gene that gives shortened transcript that are again synthesized in a tissue-specific manner. During the development of the PNS, the regulatory mechanisms of myelination are controlled by feedforward interaction of specific genes, influencing transcriptional cascades and shaping the morphology of the myelinated nerve fibers. Schwann cells are involved in many important aspects of peri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Central Nervous System
The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all parts of the bodies of bilaterally symmetric and triploblastic animals—that is, all multicellular animals except sponges and diploblasts. It is a structure composed of nervous tissue positioned along the rostral (nose end) to caudal (tail end) axis of the body and may have an enlarged section at the rostral end which is a brain. Only arthropods, cephalopods and vertebrates have a true brain (precursor structures exist in onychophorans, gastropods and lancelets). The rest of this article exclusively discusses the vertebrate central nervous system, which is radically distinct from all other animals. Overview In vertebrates, the brain and spinal cord are both enclosed in the meninges. The meninges provide a barrier to chemicals dissolv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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