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Growth Cone

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(C) Copyright 2008-2021
Dominic John Repici
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Growth Cone

In biological neural networks a growth cone is a specialized region at the axon of a developing neuron, which is found at the leading tip of the neurite's axon. The central core of a growth cone is an extension of the neurite process itself and is rich in microtubules that provide the structural support for axoplasmic transport.

Microscopic studies of the central core reveals bi-directional transport of granules. In addition, the core of the growth cone is rich in mitochondria, endoplasmic reticulum, and vesicular structures.

Surrounding the central core is a region that is very enriched in the contractile protein actin. Time lapse photography of these regions reveal the existence of undulating waves of movement ("ruffling").

Finally, very thin straight processes called microspikes or filopodia are found at the extremities. These are also rich in actin. The microspikes are in constant motion, extending from, and retracting back into the surrounding region of the core.

Growth of the neurite occurs when a microspike extends but does not retract. The area surrounding the core then moves toward the fixed end of the microspike. New microspikes then extend from this newly advanced position.

While the above video is part of a study about mercury's effects on neuronal development, it is included here because it shows actual living growth cones very clearly. It also provides a very clear illustration, which explains the underlying mechanisms and structures of the growth cone. These are the specific mechanisms that permit the growth cone to develop and move the axon forward towards a destination.

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In Netlab a growth cone is a structure on the pre-synaptic neuron responsible for the potential formation of RP connections. A particular neuron's growth-cone cone can be specified to be attracted to, and/or repulsed by, a list of named CIs. Each CI can be weighted to affect the growth cone differently and be specified as a repulsive or attractive source.

A growth-cone directs the growth of an axon from its neuron toward units (modules), and neurons that are producing attractive CIs, and away from units and neurons producing repulsive CIs. When a growth-cone nears an object (neuron) that has a Receptor Pad, the Receptor Pad settings kick in to determine whether a connection will actually be created between the pre-synaptic neuron and the target.

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In both biological and Netlab networks, growth-cones, along with repulsive and attractive CIs are part of a process of connection-making commonly called Axon Pathfinding. Biological pathfinding also relies on a wide variety of cell-cell adhesion molecules, and other guidance cues over an extracellular matrix to facilitate axon migration. Many of these mechanisms have been well documented, but may not currently be well represented in Netlab.

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biological Growth Cone

The above video shows neuron outgrowth via growth-cone pathfinding

Also: Path-finding        


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