[Studies on total nerve fivers of chorda tympani nerve in man]

An analysis of nerve fibers of the chorda tympani taken from six patients with otitis media cholesteatoma in whom the nerve could not be spared during tympanoplasty was performed. This study was designed to measure the diameter and the number of nerve fibers by making a full reconstruction of human chorda tympani in order to clarify the composition of myelinated and unmyelinated fibers, and to estimate the total number of fibers based on the results of the compartment measuring method. The following results were obtained: 1) The area of cross-section of the nerve ranged from 0.059mm2 to 0.110mm2, mean 0.081mm2. The sectional area was related to the patients age. 2) The total number of myelinated nerve fibers ranged from 3,305 to 4,668, with a mean of 3,829. The distribution of diameters of myelinated fibers had a peak at 2 to 3 microns and fibers of 1 to 4 microns accounted for 93.4% of the total. The number of myelinated fibers reduced with an increase in the patients age. 3) The total number of unmyelinated nerve fibers ranged from 2,044 to 4,334, with a mean of 3,306. The number of Schwann cell units was distributed between 791 and 1,937, with a mean of 1,386. The number of unmyelinated fibers per one Schwann cell unit ranged between 1 and 5 in 93.6% of cases. There was no age-related reduction in the number of fibers. 4) Comparing the actual measurements and the result of the compartment measuring method, the distribution of the diameter of myelinated fibers could be approximated by sampling three compartments, which area was 0.0048mm2. The total number of nerve fibers could be estimated by sampling three compartments for myelinated fibers and four compartments, one of which contained unmyelinated fibers, for unmyelinated fibers. 5) The measurement of the number of nerve fibers by the compartment measuring method and the microscopic observation indicated the locality of unmyelinated fibers. These localized fibers were speculated to be secretory fibers to hypoglossal and submandibular glands.