On the Innervation of the Membrana Tympani of Man

Abstract

Since the epidermis of the pars cutanea membranae tympani consists in a 3-4 rowed non-cornified flat epithelium, we may well expect to find intraepithelial fibres formed in it, though no papillae are found in formation beneath the epidermis. The mucous part consists of a single-rowed cubic epithelium and a thin propria in the largest part, but in its periphery, the epithelium turns into a 2-3 rowed cylindrical or ciliated one. As the mucous part represents an extension of the mucous membrane of the tympanic cavity, it is equally easy to guess that this part is also supplied with sensory nerves. Between these two parts, we find a connective tissue layer connecting them. This layer contains a well-developed outer radial sublayer and a far worse-developed inner circular sublayer.A surprisingly large number of nerve fibres are found diffused in the tympanic membrane, forming frequently unexpectedly stout nerve bundles. All these nerve bundles run out of the anulus fibrosus surrounding the tympanic membrane into the membrane and comprise some chiefly formed of thick sensory fibres and others chiefly formed of thin vegetative fibres. The former mostly come from the n. auriculotemporalis and the latter from the plexus tympanicus. Naturally, perivascular plexus of vegetative nature are also found along the blood vessels. The nerve bundles send out small branches gradually as they go from the periphery toward the center of the tympanic membrane. The upper half of the tympanic membrane is richer in nerve supply than its lower half.The chiefly sensory nerve bundles originating in the n. auriculotemporalis enter through the radial fibre layer into the corium of the cutaneous part and run therein distally toward the center of the membrane, and their branch fibres further toward the epidermis, but no such complex branched terminations or corpuscular terminations as have been mentioned in some past reports could be found in this part. Subepidermal endings were not observed either. I found that these branch fibres end mostly in sharp points closely beneath the epidermis or running further up into the epidermis as short intraepidermal fibres. Only rarely I found branched terminations formed by very thick fibres, but for these were found in a tympanic membrane taken from a senile subject, they may be assumed to have represented more or less pathological formations.The nerve bundles chiefly of fine vegetative fibres coming from the plexus tympanicus form their own plexus by ramification and mutual anastomosis, mostly in the peripheral part of the tympanic membrane. Anastomosis occurs also between these fibres and the perivascular plexus. Such plexus formation abruptly falls off as the tympanic membrane is entered, that is, the formation follows the development of the blood vessels. The vegetative fibres from these plexus, including the perivascular plexus, finally pass over into STOHR's terminal reticula, which spread out in contact with blood vessels, the connective tissue and in particular, the fibrocytes which they often penetrate right through, but they never seem to enter any smooth muscle fibre. No such periterminal net-work, as so-called by BOEKE, could be demonstrated.Sensory fibres are also found in the mucous part of the tympanic membrane. Those found in the peripheral part thereof are derived from the glossopharyngeus coming via plexus tympanicus. These sensory fibres in some cases form their terminations subepithelially, but in most cases within the epithelium here too. Beside unbranched terminations, branched terminations are often enough found in this part. The intraepithelial fibres here are somewhat different from those in the cutaneous part in that they often run peculiarly winding and rather long courses before ending.The sensory fibres found at the center of the tympanic membrane usually originate in the n. auriculotemporalis.