The paratympanic organ (PTO) is a sensory organ located in the medial wall of the tympanic cavity of birds. The organ looks like a small tapering vesicle, and is equipped with a sensory epithelium formed by supporting cells (SCs) and Type II hair cells (Type II-HCs). The function of the PTO has not yet been precisely defined. The prevailing current hypothesis is that the PTO assesses the air pressure exerted on the external surface of the tympanic membrane. The PTO could may thus function as a barometer and, in flying birds, also as an altimeter. The afferent synapses of the PTO of chicken were described in detail in a previous paper. Reciprocal synapses between efferent nerve endings (ENEs) and the HCs were also observed, suggesting the existence of local microcircuits. The aim of this work was to provide a more detailed ultrastructural description of these microcircuits in the PTO of chicken. We observed for the first time: (1) reciprocal synapses between the HCs and the afferent nerve endings (ANEs); (2) presence of two distinct types of ENEs; (3) reciprocal synapses between the HCs and both types of ENEs. Overall, these results indicate that a complex processing of the incoming sensory signals may occur in the PTO. This thus suggests that the PTO may perform more complex functions than those supposed until now. We hypothesize that the PTO could have a role in the low-frequency sound perception.

中文翻译：

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鸡鼓膜旁器官感觉上皮中神经微电路的超微结构研究。

鼓膜旁器官（PTO）是位于鸟类鼓膜腔内壁的感觉器官。该器官看起来像一个逐渐变细的小囊泡，并配有由支持细胞（SCs）和II型毛细胞（II-HCs型）形成的感觉上皮。PTO的功能尚未精确定义。当前流行的假设是，PTO评估施加在鼓膜外表面的气压。因此，PTO可以用作气压计，在飞鸟中也可以用作高度计。鸡的PTO的传入突触在先前的论文中有详细描述。还观察到传出神经末梢（ENE）和HC之间的相互突触，表明存在局部微电路。这项工作的目的是为鸡的PTO中的这些微电路提供更详细的超微结构描述。我们首次观察到：（1）HCs与传入神经末梢（ANEs）之间存在相互的突触；（2）存在两种不同类型的ENE；（3）HC和这两种ENE之间的相互突触。总体而言，这些结果表明，在PTO中可能会对传入的感觉信号进行复杂的处理。因此，这暗示着PTO可能会执行比目前设想的功能更为复杂的功能。我们假设PTO可能在低频声音感知中起作用。（3）HC和这两种ENE之间的相互突触。总体而言，这些结果表明，在PTO中可能会对传入的感觉信号进行复杂的处理。因此，这暗示着PTO可能会执行比目前设想的功能更为复杂的功能。我们假设PTO可能在低频声音感知中起作用。（3）HC与这两种ENE之间的相互突触。总体而言，这些结果表明，在PTO中可能会对传入的感觉信号进行复杂的处理。因此，这暗示着PTO可能会执行比目前设想的功能更为复杂的功能。我们假设PTO可能在低频声音感知中起作用。