耳石器と頸部深部受容器

To understand better the correlation between the cervical proprioceptors and the otolith, in the development of eye nystagmus of cervical origin, the following two series of experiments were carried out using rabbits.<br>Experiment A: Rabbits with healthy ears were placed in the following five postures and eye deviation and/or eye nystagmus induced in these postures were recorded from the right eye using electronystagmograph (ENG) and the electromyographs (EMG's) of the bilateral deep neck muscles were also recorded. The 1st posture: a piece of cloth is wrapped around the trunk of a rabbit to suspended it in the air so that its four limbs do not touch the ground. The 2nd posture: the animal's head is in the normal position and the trunk and limbs are rotated 90 degrees counterclockwise around the longitudinal axis of the body. The 3rd posture: the animal's trunk and limbs are in the normal position and the head is then rotated 90 degrees clockwise around the longitudinal axis of the body. The 4th posture: the animal's whole body is laid down on the left side. The 5th posture: the animal's head is in the normal position and the trunk and limbs are then rotated above 90 degrees counterclockwise around the longitudinal axis of the body. In experiment A, the following facts were noted.<br>(1) In the 1st posture, neither asymmetry in the activity of the bilateral deep neck muscles nor eye movement was observed.<br>(2) In the 2nd posture, only eye deviation was induced together with increased activity of the unilateral deep neck muscles, whereas in the 5th posture, eye nystagmus was elicited.<br>(3) In the 4th posture, deviation of the eyes, i. e., compensatory eye deviation of otolithic origin developed together with increased activity of the unilateral deep neck muscles.<br>(4) In the 3rd posture, development of eye nystagmus was the most conspicuous, together with a marked increase in the activity of the unilateral deep neck muscles.<br>From these results, we conclude the following.<br>First, the cervical proprioceptors can induce nystagmic responses, whereas the otolith induces only eye deviation. Second, the otolith can play a major role in the enhancement of nystagmus of cervical proprioceptive origin.<br>Experiment B: Rabbits with healthy ears are placed in the following four postures and eye deviation and/or eye nystagmus induced in these postures are recorded from the right eye using ENG. The four postures referred to herein are as follows. The 1st posture: the same posture as the 1st posture described in experiment A. The 2nd posture, the animal's whole body is rotated counterclockwise on the sagittal plane with its nose up. The 3rd posture, the animal's head is in the normal position and the trunk and limbs are then rotated clockwise on the sagittal plane with its tail up. The 4th posture, the animal's trunk and limbs are in the normal position and the head is then rotated counterclockwise on the sagittal plane.<br>In experiment B, the following facts were noted.<br>(1) In the 2nd posture, deviation of the eyes, i. e., compensatory eye deviation of otolithic origin developed around the bitemporal axis of the body.<br>(2) In the 3rd posture, rotatory eye nystagmus developed around the bitemporal axis of the body. The nystagmus thus induced was small in amplitude and low in frequency.<br>(3) In the 4th posture, rotatory eye nystagmus developed around the bitemporal axis of the body. The nystagmus thus induced became larger in amplitude and frequency when compared to that of the 3rd posture.<br>On the basis of these results, we conclude that the otolith does play an important role in the enhancement of nystagmic responses of cervical proprioceptive origin.