Once differentiated neurons migrate over considerable distances sometimes, before moving on to the extension of their dendrites and their axons phase. Nature has developed a variety of strategies to this end, including the training of guide rails for neurons, such as those formed by the radial glia cells that is to say, the neural tissue. These cells have a long cylindrical extension, which may be several millimeters in length (for a fraction of a micron in diameter), along which neurons grew until they receive a signal to stop. This method allows to guide a large number of neurons in a same direction and thereby forming structures where neurons are layered (for example, the gray matter of the cerebral cortex).
Once at their destination, the neuron will extend its neurites. During the extension phase, the end
neurneuriteitic differentiates to form a highly specialized called growth cone (cf.DEVELOPMENT Biology) structure. This structure has the necessary machinery for the elongation neurite (axon or dendrite). It is bristling with short extensions tapered charged to explore the immediate vicinity of the growth cone in search of chemical signals. The guidance signals can be positive (permissive or attractive) or negative (inhibitory or repulsive). Each of these signals has to be carrier molecules embedded in the living tissue, which defines precisely their location, is freely diffusing, which defines a spatially extended gradient. Each growth cone and receives a multitude of signals, possibly conflicting, whose sum determines its navigation in the nervous tissue.
The extension of axons is generally broader than the dendrites. The elongation of axons and their guide for considerable distances are facilitated by two types of mechanisms. On the one hand, their journey is full of relay groups, closely spaced cells between which they form a straight segment at which they take policy decisions or branching. other hand, the nerve tissue is constructed in several steps, the first used for the execution of the following. The earliest axons growing isolation in the living tissue, as the embryo is small. Thereafter, the new axons evolve into a network of beams formed by early axons. Growth cones follow the paths defined by the beams optionally switching from one beam to another at specific points decision.
At the end of his long journey, it often happens that the axon is divided into several branches in the target region. Growth cones receive a stop signal and turn into synaptic terminal. Synaptic terminals appear as bulges placed on the target cell. The axons generally do not connect to all types of neurons that exist in the region of their endings, and this is still the molecular signaling that determines the neurons that connect the axons.
Once at their destination, the neuron will extend its neurites. During the extension phase, the end
neurneuriteitic differentiates to form a highly specialized called growth cone (cf.DEVELOPMENT Biology) structure. This structure has the necessary machinery for the elongation neurite (axon or dendrite). It is bristling with short extensions tapered charged to explore the immediate vicinity of the growth cone in search of chemical signals. The guidance signals can be positive (permissive or attractive) or negative (inhibitory or repulsive). Each of these signals has to be carrier molecules embedded in the living tissue, which defines precisely their location, is freely diffusing, which defines a spatially extended gradient. Each growth cone and receives a multitude of signals, possibly conflicting, whose sum determines its navigation in the nervous tissue.
The extension of axons is generally broader than the dendrites. The elongation of axons and their guide for considerable distances are facilitated by two types of mechanisms. On the one hand, their journey is full of relay groups, closely spaced cells between which they form a straight segment at which they take policy decisions or branching. other hand, the nerve tissue is constructed in several steps, the first used for the execution of the following. The earliest axons growing isolation in the living tissue, as the embryo is small. Thereafter, the new axons evolve into a network of beams formed by early axons. Growth cones follow the paths defined by the beams optionally switching from one beam to another at specific points decision.
At the end of his long journey, it often happens that the axon is divided into several branches in the target region. Growth cones receive a stop signal and turn into synaptic terminal. Synaptic terminals appear as bulges placed on the target cell. The axons generally do not connect to all types of neurons that exist in the region of their endings, and this is still the molecular signaling that determines the neurons that connect the axons.
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