While applying solutions of 5 mm QHCl, 2 M NaCl and HCl at pH 2.0 to three different ipsilateral portions, root, middle and tip of the tongue surface of the frog, reflex discharges were recorded from three main branches of the hypoglossal nerve. Reflex discharges in the hyoglossal branch were elicited mainly when the caudal two-thirds of the tongue was stimulated with the chemicals, whereas those in the genioglossal branch occurred predominantly when the rostral two-thirds of the tongue was stimulated. The intrinsic branch responded reflexly to stimulation of any portion of the tongue. The hyoglossal branch was also highly sensitive to mechanical stimulation of the tip of the tongue.
Action potentials reflexly elicited by electrical stimulation of medial and lateral branches of the glossopharyngeal nerve were recorded from the following two of the three efferent branches simultaneously. Then it was revealed that the activity of the hyoglossal branch was induced by sensory inputs from low threshold fibers in the medial branch, whereas that of the genioglossal branch was mainly by the lateral branch.
Latencies between the electrical stimulation of the afferent branches and the action potential of the efferent branches were measured. The onset of the potential in the hyoglossal branch produced by stimulation of the medial branch had the shortest latency. This reflex arc may functionally play a role in retracting the tongue quickly after capturing a prey at the tip of the frog tongue.