Nerves / by David Fraser-Harris.

  • David Fraser Fraser-Harris
Date:
[1928]
Catalogue details

Licence: In copyright

Credit: Nerves / by David Fraser-Harris. Source: Wellcome Collection.

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    forms of “ external ” energy—pressure, ther¬ mic change, light, sound, etc., in other words, the afferent nerves are related either to environmental changes or to changes of bodily condition ; these constitute the stimu¬ lation. In afferent nerve-fibres what happens after stimulation is that nerve-impulses ascend. Nothing, therefore, except nerve-impulses arrives in the central nervous system, so that only nerve-impulses can be the sources of stimulation of the neurons within or leaving the nervous system. Therefore the normal, physiological stimuli for neurons arising in the nervous system are exclusively nerve- impulses, and these affect only the nerve-cells which give origin to the outgoing nerve-fibres. Now it will be seen that, normally, both afferent and efferent neurons are stimulated only at their origins, the former in the tissues, the latter in the central nervous system. If, however, either sort of neuron happens to be stimulated (irritated) at any point in its path, nerve-impulses will ascend or descend the neuron just as though it had been stimu¬ lated at its origin under normal conditions. Thus, if I get a blow on my elbow just wdiere the sensory nerve from the fingers is near the surface, I have a distinct sensation
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