Physiology and biochemistry in modern medicine . strictly in consonance with the neuron such is not the case, however, is shown by the fact observed byNinian Bruce4 that irritants such as mustard oil applied to the skinor cornea continue to produce their usual reaction for some time after 796 THE PROPERTIES OF E3AOH PART OK THE REFLEX AUr 797 section of the posterior roots of the spinal cord, but fail to do so ifthe nerve libers are cut and allowed 1 degenerate, or if the stimuli areblocked by applying cocaine to the skin. What actually happens isevidently that the impulse set
Physiology and biochemistry in modern medicine . strictly in consonance with the neuron such is not the case, however, is shown by the fact observed byNinian Bruce4 that irritants such as mustard oil applied to the skinor cornea continue to produce their usual reaction for some time after 796 THE PROPERTIES OF E3AOH PART OK THE REFLEX AUr 797 section of the posterior roots of the spinal cord, but fail to do so ifthe nerve libers are cut and allowed 1 degenerate, or if the stimuli areblocked by applying cocaine to the skin. What actually happens isevidently that the impulse set up by the irritant as it travels up the.•liferent fiber passes on to one of the branches above referred to, alongwhich it then proceeds to the blood vessels, which it causes to such vasodilator impulses may be transmitted down the fibers ofan afferent nerve has been confirmed by Bayliss, who found that vaso-dilatation occurred in the hind limb when the posterior spinal rootswere stimulated (see page 234). Post, Fig. 206.—Diagram to show axon reflex of sensory nerve fiber of skin. A stimulus applied tothe skin is transmitted by the sensory fiber (.¥),* part of it going to the spinal cord (SC), andpart of it passing by the collateral (C) to the arteriole {A), which it causes to dilate. In this peripheral branching of the afferent fibers of the skin, wehave therefore a sort of neuropile which, like that of certain forms ofCelenterates (see page 782), is capable of serving as a pathway for thetransmission of a sensory impulse to an effector organ without the in-tervention of nerve cells. Such a reflex is known as an axon reflex, andit is evident that it may occur through any fiber which gives off branches,one traveling to a sensory surface, the other to some effector organ, asoccurs in the hypogastric nerves to the bladder (see page 883). THE SYNAPSIS At the point of contact between a branch of one neuron and a nervecell of the next, we have seen that t
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