An American text-book of physiology . central cells: C,C, CC . C C , neuronscells the bodies of which are located in other segments ; E, efferent cell. pulses which do produce the discharge is by no means the only pathway overwhich the impulses can or do travel. u • i The most convenient illustration of this process of diffusion can be obtainedby a study of the knee-kick or knee-jerk as it is more commonly reaction in question consists in a contraction of extensor muscles of theknee in consequence of a blow on the tendon just below the knee-pan. Asa result of this contraction, the l
An American text-book of physiology . central cells: C,C, CC . C C , neuronscells the bodies of which are located in other segments ; E, efferent cell. pulses which do produce the discharge is by no means the only pathway overwhich the impulses can or do travel. u • i The most convenient illustration of this process of diffusion can be obtainedby a study of the knee-kick or knee-jerk as it is more commonly reaction in question consists in a contraction of extensor muscles of theknee in consequence of a blow on the tendon just below the knee-pan. Asa result of this contraction, the leg is extended, and a kick of greater or lessextent is made from the knee joint. Very careful studies of the conditionscontrolling this response have been made by a number of Westphal,^ Lombard,^ Bowditch and Warren,^ Weir-Mitchell, 1 Archiv filr Psychiatrk, 1875.» Joumd of Physiology, 1890. 2 American Journal of Psychology, 1887.* Philadelphia Medical News, Feb., 1886. 650 AK AMERICAN TEXT-BOOK OF Fig. 170.—Record of the knee-kick of a tkineiitedpatient. The knee tapped at regular intervals offive seconds. While the patient was asleep and allabout was quiet, no response was obtained; after suchan irresponsive period the sound of some one walkingon the floor below caused at ^ a series of kicks whichgradually diminished; the same at B. At C two tapswith a pencil and a distant locomotive-whistle produceda longer series. The arrow indicates the direction inwhich the record is to be read (Noyes). Noyes.^ It is fouiul tlmt under given conditions, the variations in theextent of the kick can be referred to variations in the excitability of tliatportion of the spinal, cord from which the fibres controlling the muscles take their origin, namely, the second,third, and fourth lumbar seg-ments. In the same individual underconstant conditions and for shortperiods of time, the knee-kickmay be fairly constant in its ex-tent, but the normal extent for
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