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Перевод: axon

аксон

Тезаурус:

1. By studying a series of successively younger embryos he found that the same cells at the tip of the limbs always contacted the central nervous system first, and that subsequent connections were always made along pathways established by the axon processes extended by these pioneer cells.
2. Intriguingly, in a few cases Raper found that the G and C cells became linked to the axon they would Follow just before the turn was made.
3. One or more of these processes forms a long conducting fibre or axon (Narahashi, 1963) ending in a group of fine, branching fibrils; the number of axons enables the neuron to be classified as uni-, bi- or multipolar.
4. From the cell body of a neurone there emerge two kinds of processes: relatively short dendrites which carry messages towards the cell body, and a single axon, which may be a metre in length, although in the brain it is usually much shorter, which carries signals away from the cell body.
5. There is also a dual innervation, with a fast axon supplying all or most of the fibres in a muscle while a slow axon innervates a proportion of them.
6. Activation of this third type of neurone has the effect of increasing the amount of neurotransmitter released at the synapse between sensory and motor neurones, for each nerve impulse travelling down the axon of the sensory cell.
7. A given sensory cell is connected to many axons in the optic nerve, and each axon in the optic nerve receives inputs from many sensory cells.
8. The rate of propagation varies from one to a hundred metres per second, depending on the diameter of the axon.
9. Neurones connect with one another via "synapses", where an end branch of an axon comes into contact with a cell body or dendrite of another neurone.
10. During embryogenesis Schwann cell progenitors migrate from the neural crest, then proliferate along tracts to be occupied by peripheral axons where they support axon extension.
11. The "signal" which travels from the cell body out along the axon is an electrical nerve impulse.
12. The results of these cross-connections can be discovered by recording the impulses in a single axon in the optic nerve, while illuminating the retina in different ways.