Elsevier

Experimental Neurology

Volume 1, Issue 4, October 1959, Pages 334-359
Experimental Neurology

Sensory nerves of the cornea and cutaneous sensibility

https://doi.org/10.1016/0014-4886(59)90025-1Get rights and content

Abstract

Action potentials evoked in the afferent nerves by application of mechanical and thermal stimuli to the cat's cornea were studied to determine if the nerve terminals in the cornea are physiologically specialized. The intensities of stimuli used were such that, when applied to the human cornea, reports of touch, warmth, cold, and pain were evoked. Each of the long ciliary nerves contains approximately five hundred fibers of which about forty are 6 μ or more in diameter, five or six supplying the cornea. In the cornea, smaller fibers are distributed over larger areas than the larger fibers. Areas of distribution of long ciliary nerves overlap one another. No action potentials are recorded from these nerve fibers unless the cornea is being stimulated, irrespective of the temperature (25° to 45°C) at which the preparation has been stabilized. Both mechanical and thermal stimuli evcke activity in the long ciliary nerve when applied within the area of its distribution. The frequency and temporal distribution of the activity is related to the stimulus applied. Mechanical stimuli applied to the cornea evoke an immediate high frequency outburst in 3 to 6 units which ceases abruptly on withdrawal of the stimulus. In response to thermal stimulation—both positive and negative—the activity starts after a short delay which varies inversely with the strength of the stimulus. The frequency of impulse discharge and the duration of activity vary directly with the stimulus strength. The same units that respond to mechanical stimulation become active on thermal stimulation. Some units discharge impulses more readily to negative thermal stimuli and others to positive, but the majority, equally well to either. Electrical depolarization of terminals in the active zone of cornea causes all the fibers in that zone to discharge impulses. The maximum number of units in a long ciliary nerve thrown into activity by depolarization corresponds to that discharging in response to mechanical and thermal stimuli.

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    2

    Dr. Lele's present address is: Medical Acoustics Research Group, Massachusetts General Hospital, Boston, Massachusetts.

    1

    Our thanks are due to Dr. Ludwig von Sallmann and Dr. W. Ross Adey for much helpful advice; and Miss Patricia Grimes for assistance in the preparation of the manuscript. This investigation was supported by a grant to one of us (G. W.) from the Rockefeller Foundation.

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