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[3] [4] [5] Once there, the electrical signal provokes the release of chemical neurotransmitters across the synapse, which bind to receptors on the post-synaptic cell (e.g. another neuron, myocyte or secretory cell). Myelin is made by glial cells, which are non-neuronal cells that provide nutritional and homeostatic support to the axons
Group A are heavily myelinated, group B are moderately myelinated, and group C are unmyelinated. [1] [2] The other classification is a sensory grouping that uses the terms type Ia and type Ib, type II, type III, and type IV, sensory fibers. [1]
Transmission electron micrograph of a myelinated axon Neuron with oligodendrocyte and myelin sheath showing cytoskeletal structures at a node of Ranvier. The basic helix–loop–helix transcription factor OLIG1 plays an integral role in the process of oligodendrocyte myelinogenesis by regulating expression of myelin-related genes. OLIG1 is ...
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.
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 from 0.5 to 10 m/s). [1]
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.
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 ...
These occur when a non-myelinating Schwann cell bundles the axons close together by surrounding them. [4] The Schwann cell keeps them from touching each other by squeezing its cytoplasm between the axons. [4] The condition of Remak bundles varies with age. [4] The number of C fiber axons in each Remak bundle varies with location. [3]