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The fastest recorded conduction speed (across both vertebrates and invertebrates) is found in the ensheathed axons of the Kuruma shrimp, an invertebrate, [15] ranging between 90 and 200 m/s [16] (cf. 100–120 m/s for the fastest myelinated vertebrate axon).
There are two types of axons in the nervous system: myelinated and unmyelinated axons. [5] Myelin is a layer of a fatty insulating substance, which is formed by two types of glial cells: Schwann cells and oligodendrocytes. In the peripheral nervous system Schwann cells form the myelin sheath of a myelinated axon. Oligodendrocytes form the ...
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.
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]
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]
The optimal ratio of axon diameter divided by the total fiber diameter (which includes the myelin) is 0.6. [24] Oligodendrocytes in rat cerebellum stained with antibody to myelin basic protein in red and for DNA in blue. Two oligodendrocyte cell bodies are clearly visible as well as several myelinated axons.
Nerves may be myelinated or unmyelinated. Myelinated nerves have the axon covered by segments of schwann cells, which are short and concentrically wrapped around the diameter of an axon to give the appearance of a sausage-like mass and called a myelin sheath. The schwann cells are arranged in pattern such all parts of the axon are wrapped in ...
Therefore, most neural pathways are made up of axons. [citation needed] If the axons have myelin sheaths, then the pathway appears bright white because myelin is primarily lipid. [citation needed] If most or all of the axons lack myelin sheaths (i.e., are unmyelinated), then the pathway will appear a darker beige color, which is generally ...