ACCOMMODATION AND AUTORHYTHMIC MECHANISM IN SINGLE SENSORY FIBRES

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Abstract
The repetitive discharge in response to slowly rising linear stimuli was recorded with the aid of micro-electrodes from cutaneous and muscular afferents. Single fibres could be isolated by placing the micro-electrode on the dorsal roots. Stimulus form and nerve response were pictured simultaneously with the aid of a double cathode ray oscillograph on the same film. By this method it was possible to measure the sensory accommodation curves directly and at the same time to correlate them with the properties of the iterative discharge. There is little if any accommodation in n. saphenous, representing cutaneous afferents (Hill''s constant [lambda] approaching infinity). For different muscular twigs of n. popliteus the values for X range from 150-200 msec. The autorhythmic discharge caused by the slowly rising stimuli consists of an initial phase during the time the stimulus rises and a later plateau-phase when the stimulus has reached a certain plateau level of strength. These 2 phases may be separated by a "silent period." "The plateau discharge is characterized by a frequency which increases with stimulus strength. The strength-frequency curve for single fibres is illustrated. It is independent of the accommodative resistance of the nerve. The total adaptation time (from first to last impulse) of the plateau discharge is a function of accommodation and of stimulus strength and decreases when the accommodative resistance increases or stimulus strength decreases. These relations are illustrated quantitatively for nerves of different accommodations. Strong stimuli continued on plateau height inhibit the discharge (Schiff-Werigo''s cathodal depression), provided that the nerves possess good accommodative resistance. It is suggested that the total adaptation time is largely detd. by this factor. The slowly rising stimulus sometimes causes a rhythmically grouped discharge instead of a continuous flow of impulses.

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