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Myelinated fibers lack voltage-gated sodium channels along the myelinated internodes, exposing them only at the nodes of Ranvier. Here, they are highly abundant and densely packed. [25] Positively charged sodium ions can enter the axon through these voltage-gated channels, leading to depolarisation of the membrane potential at the node of Ranvier.
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 (OPCs) or Schwann cell progenitors into their mature counterparts, [4] followed by myelin formation around axons.
Neurilemma (also known as neurolemma, sheath of Schwann, or Schwann's sheath) [1] is the outermost nucleated cytoplasmic layer of Schwann cells (also called neurilemmocytes) that surrounds the axon of the neuron. It forms the outermost layer of the nerve fiber in the peripheral nervous system. [2]
Since an axon can be unmyelinated or myelinated, the action potential has two methods to travel down the axon. These methods are referred to as continuous conduction for unmyelinated axons, and saltatory conduction for myelinated axons. Saltatory conduction is defined as an action potential moving in discrete jumps down a myelinated axon.
White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called tracts. [1] Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distribution of action potentials, acting as a relay and coordinating communication between different brain ...
Along myelinated nerve fibers, gaps in the myelin sheath known as nodes of Ranvier occur at evenly spaced intervals. The myelination enables an especially rapid mode of electrical impulse propagation called saltatory conduction. The myelinated axons from the cortical neurons form the bulk of the neural tissue called white matter in the
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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. [1] The colour difference arises mainly from the whiteness of myelin. In living tissue, grey matter actually ...