Nervous control of the cat nictitating membrane

¹ Department of Physiology, University of Illinois, Urbana, Illinois

The nonstriated muscle fibers of the nictitating membrane respond to a single volley of nerve impulses with a slow twitch and three potentials: two independent waves followed by slow oscillations. On repetitive stimulation, the potentials overlap and sum algebraically. Pressure electrodes record only extracellular potentials. The first wave is elicited by nerve fibers which have a higher average threshold than the fibers which elicit the second wave. Eserine potentiates and hyoscine antagonizes the first wave. Dibenzyline, piperoxan, and reserpine antagonize the second wave. The nictitating membrane has functional adrenergic and cholinergic innervations; both cause retraction. Facilitation and summation can be either spatial, through the double innervation of each cell, or temporal, by diffusion of the transmitters from one cell to another. The cholinergic response is not maximal when the adrenergic response is maximal. The second wave is not potentiated by eserine at the same time as or before the potentiation of the first wave. Thus cholinergic innervation of adrenergic stores cannot explain the two electrical waves.