Studies of the optic nerve of the rhesus monkey: Nerve fiber spectrum and physiological properties

This report describes a combined study of the anatomy and physiology of the optic nerve of the rhesus monkey. An optic nerve was fixed in osmium tetroxide and embedded in epon for the histological study: 60,898 fibers were measured and tabulated according to outside diameter. The fiber spectrum was unimodal with a peak frequency at 1·2 μ and a range of 0·4-6 μ. The total number of fibers was 1,410,000. The compound action potentials of the entire optic nerve and of small fascicles of the optic nerve were recorded at the optic disk; conduction velocities, recovery cycles and afterpotentials were studied. These properties of the nerve fibers showed a continuous range of values which were associated with differences in fiber diameter. It is concluded that the fibers of the optic nerve form a homogeneous population; thus the anatomical and physiological findings are not in conflict. Differences between the properties of fibers in the optic nerve and in the retina are described and discussed in terms of the known ultrastructure of the retinal nerve fiber layer.