INNERVATION OF THE SMOOTH MUSCLE IN THE CERVICAL TRACHEA

Abstract

The efferent pathway of reflexive change of tracheal muscular tonus seen on stimulation of the nasal and laryngeal mucosa was investigated in the cervical trachea of the dog.A sort of mechanical plethysmography described by Kahn (1907) and Nadel et al. (1962) was used in order to record the response of the tracheal muscle.Thirteen dogs were examined under chloralose and urethane anesthesia with muscle relaxant and artificial respiration.The cervical trachea was detached from the larynx and the lower trachea preserving the vessels and the nerves including the inner branch of the superior laryngeal nerve (S.L.N.), the inferior laryngeal nerve (I.L.N.) and the anastomosing branch of Gallen.This tracheal segment was made airtight. The change of tracheal volume by contraction or dilatation of the tracheal muscle was recorded on the Visicorder through the pressure transducer (Statham PM 15) and the amplifier.The degree of dilatation and contraction of the trachea by sectioning and electrically stimulating the branches of S.L.N. and LL.N. were measured and compared.The effect of sectioning individual efferent nerves on reflexive contraction of the tracheal muscle seen by electrically stimulating the cut proximal end of the inner branch of the S.L.N. was measured.The present experiment revealed the following findings.1. The efferent pathway to the cervical tracheal muscle runs through the anastomosing branch of Gallen.This consists of descending nerve fibers passing through the posterior branch of the inner branch of the S.L.N. and the ascending nerve fibers passing through the posterior branch of the I.L.N. The decending nerve fibers innervate the upper 1/2-1/3 of the cervical tracheal muscle. On the other hand the ascending nerve fibers innervate its inferior 1/2-1/3.2. The most remarkable contraction of the cervical trachea in most dogs was observed with stimulation of the right posterior branch of the I.L.N. In 23% of the the dogs, however, the stimulation of the inner branch of the right S.L.N. caused the most remarkable contraction of the trachea. This was consistent with dilatation of the trachea and decrease of reflexive contraction of the I.L.N. noted by sectioning the efferent nerve. The anterior branch of I.L.N. does not contain motor fibers to the cervical tracheal muscle.3. The difference of innervation in the cervical trachea between the right and left efferent nerves was apparent, with marked predominance of the right efferent nerves.