Rhythmical and non-rhythmical spontaneous activity recorded from the central cut end of the sinus nerve.

1. Two types of spontaneous nervous activities have been recorded from the central cut end of the carotid sinus nerve of the cat.2. One type was composed of nerve potentials that exhibited a respiratory or cardiac rhythm, whose rate of firing was depressed by the pressor response to adrenaline, and that were found to arise from post-ganglionic fibres of the superior cervical ganglion.3. The other type of activity consisted of non-rhythmical nerve potentials whose rate of discharge increased 10-30 sec after the injection of adrenaline. The activity of these fibres also increased when the arterial oxygen tension was lowered or when the arterial carbon dioxide tension was raised.4. It is conceivable that either of these two groups of fibres, rather than the chemoreceptor afferent fibres, could provide the source of the microvesicle-containing nerve endings on the type 1 cells of the carotid body.5. A nerve was also described coursing from the sinus nerve to the hypoglossal nerve; the activity in it was sympathetic in origin.