Zusammenfassung
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1.
Ein neuer Typ von Mechanorezeptoren bei Crustaceen wird beschrieben. Die bi- oder tripolaren Zellkörper dieser Rezeptoren liegen in den proximalen Abschnitten der ersten und zweiten Nervenstämme eines jeden Schwanzsegmentes des Krebses. Die Dendriten erstrecken sich bis in die Hypodermis der weichen Bauchhaut, insbesondere im Bereich der Insertion der tonischen Beugemuskeln, und in die Basalglieder der Körperanhänge.
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2.
Elektrophysiologische Ableitungen und Vitalfärbungen zeigen, daß die sich reich verzweigenden Dendriten oft in weit voneinander getrennte Areale der Haut ausstrahlen. Die dendritischen Endigungen in den sensitiven Hautbereichen weisen spindelförmige Auftreibungen auf.
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3.
An einer bestimmten Endstruktur ausgelöste Impulse wandern in alle übrigen Verzweigungen ein. Die Refraktärzeit der Endstrukturen ist 6–7 ms. Das kürzestmögliche Interval, mit dem zwei Endstrukturen erfolgreich nacheinander (zeitliche Folge in beiden Richtungen) gereizt werden können, läßt Rückschlüsse auf die Form der Verzweigung dieser Dendriten zu.
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4.
Die über die ganze Dendritenlänge gemittelte Leitgeschwindigkeit ist mindestens 0,6–0,8 m/s. Der dicke proximale Teil des Dendriten entspricht in seiner Leitgeschwindigkeit (ca. 1,5 m/s) dem Axon.
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5.
Die Afferenz dieser Rezeptoren verursacht eine reflektorische Hemmung der Entladungsrate der zu den tonischen Beugemuskeln und Pleopodenmuskeln führenden Motoneurone. Natürliche Reizung der sensiblen Hautbereiche oder elektrische Reizung kleiner Nervenäste, die Dendriten der Rezeptoren enthalten, können diesen Reflex auslösen.
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6.
Eine Gruppe einzeln identifizierbarer Interneurone im Bauchmark wird durch die mechanorezeptorischen Afferenzen aus verschiedenen Segmenten aktiviert und verursacht ebenfalls in verschiedenen Segmenten Änderungen der Entladungsrate von Motoneuronen.
Summary
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1.
A new class of crustacean mechanoreceptors is described. Their bipolar or tripolar somata are located in the proximal region of the first and second ganglionic roots in each abdominal segment of the crayfish. These cells send dendrites into the hypodermis of the soft cuticle associated with the insertions of the superficial flexor muscles and the bases of the appendages.
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2.
Both electrical recording and supravital staining indicates that the dendrites of these cells branch extensively, and innervate several areas of cuticle that are often widely separated. Sensory areas are rich in dendritic terminals that bear distal expansions.
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3.
Impulses initiated at a given terminal invade all others by axon reflex; the refractory time for the terminals is 6–7 msec. The minimal interval at which two terminals may be stimulated for both possible sequences may be used to infer the morphology of the branching pattern for those dendrites.
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4.
Average dendritic conduction velocity is 0.6–0.8 m/sec; the fine peripheral terminations undoubtedly conduct much more slowly, since this figure includes a thick proximal portion which conducts at a speed of 1.5 m/sec.
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5.
This class of mechanoreceptors produces reflex suppression of motor discharge to the postural flexor muscles and to the swimmerets. The reflex may be evoked by natural stimulation of the sensory area or by electrical stimulation of small nerve branches containing dendrites of the receptor neurons.
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6.
The central influence of this sensory system is spread by a class of individually identifiable interneurons, each of which collects input from several segments and also produces motor effects in several.
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Supported in part by grants (to D. K.) from the U.S. Air Force Office of Scientific Research (AFOSR-334-66) and from the U.S. Public Health Service (NB 02944). The authors gratefully acknowledge the technical assistance of Mrs. Philip Hanawalt.
Supported in part by a fellowship from the Volkswagen Foundation.
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Pabst, H., Kennedy, D. Cutaneous mechanoreceptors influencing motor output in the crayfish abdomen. Z. Vergl. Physiol. 57, 190–208 (1967). https://doi.org/10.1007/BF00303073
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DOI: https://doi.org/10.1007/BF00303073