Some Pacemaker Aspects of Rhythmic Activity in the Nervous System

A physiological pacemaker is usually regarded as a region of an organ or tissue from which arises rhythmic activity without the intervention of an external stimulating agent. Thus the sinoauricular node is spoken of as the pacemaker of the vertebrate heart. The physicochemical nature of pacemaker determinations of rhythms is of considerable importance. Pacemaker conditions may be established experimentally in excitable tissues. The application of a drop of chloroform to a Nitella cell may, by locally reducing the resting potential, set up local circuits between the normal and treated tissue which start waves of action currents along the cell. These waves may be rhythmically repeated as soon as the tissue recovers from the refractory state set up by the previous impulse (40). In like manner a drop of 0.05M KC1, by locally reversing the resting potential of Nitella, acts to produce a pacemaker locus. The ends of certain cut...