Three major groups arise from this classification: multipolar, bipolar, and unipolar neurons. Structural classification of neurons is based upon the number of processes that extend out from the cell body. Title: Neuron-figure-notext.svg Author: Nicolas.Rougier Site: License: This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. The body will go to great lengths to ensure that neurons are adequately fed in fact, if for some reason the brain detects that it is not receiving adequate amounts of nutrition, the body will shut down immediately (i.e., faint). Neurons also have exceptionally high metabolic rates and subsequently require high levels of glucose and oxygen. Perhaps the slow recovery rate or lack of regeneration is to ensure that learned behavior and memories are preserved throughout life.
For this reason, there is usually limited recovery from serious brain or spinal cord injuries. Still, if a neuron is damaged or lost, it is not easily replaced. Fortunately, lifespans of amitotic neurons is near 100 years. Exceptions to this rule are found in olfactory neurons (those associated with smell) and hippocampal regions of the brain. Most neurons are amitotic or lose their ability to divide. The axon terminal is designed to convert the electrical signal into a chemical signal in a process called synaptic transmission (further explained in the section "Physiology of the Neuron"). Image shows Anterograde and Retrograde transport in an axon.Īxon terminals: Once an axon reaches a target, it terminates into multiple endings, called axon terminals. Image produced by BYU-Idaho Student Jared Cardinet 2013 These are essential for electrical insulation and to speed up action potential propagation.
Myelin consists of totally separate cells that coil and wrap their membranes around the outside of the axon. This system can move materials down the axon at rates of 400mm/day (see lowest figure). Specialized motor proteins "walk" along the microtubules, carrying material away from the soma (anterograde transport) or back to the soma (retrograde transport). Microtubules are arranged inside the axon as parallel arrays of long strands that act as highways for the movement of materials to and from the soma. Because of this length, the axon contains microtubules and is surrounded by myelin. In contrast to the shorter dendrites, the axon can extend for more than a meter. Dendrites function to receive information, and do so through numerous receptors located in their membranes that bind to chemicals, called neurotransmitters.Īxon: An axon is a large process that extends from the cell body at a point of origin-called the axon hillock-and functions to send information. Neurons have four specialized structures that allow for the sending and receiving of information: the cell body (soma), dendrites, axon and axon terminals (see lowest figure).Ĭell body or soma: The cell body is the portion of the cell that surrounds the nucleus and plays a major role in synthesizing proteins.ĭendrites: Dendrites are short, branched processes that extend from the cell body.
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