Nerve trunk excitability and excitability of individual nodes of Ranvier in frog nerve fibers.

It has been found that the duration of the absolute and relative refractory phases at individual nodes of Ranvier in myelinated nerve fibers is longer (by 39 and 33%, respectively) than in the nerve as a whole. In addition, at individual nodes of Ranvier in isolated nerve fibers the phases of facilitation and prolonged subnormality are absent. If, however, one prepares single nerve fibers taking precautions against stretching the node of Ranvier (preparations with "closed" and "sheltered" nodes), one may observe in them both facilitation and prolongation of the subnormal phase. It has been concluded that the procedure for preparing single nerve fibers leads to substantial changes in the functional properties of the excitable membrane at the node of Ranvier and disturbs the integrity of the surrounding ionic barrier.