Paired postanal lateral chemoreceptor sensory organs. A chemoreceptor present on the aortic arch. This activates 5-HT3 receptors in the chemoreceptor trigger zone that stimulate vomiting. In this way, transduction in peripheral chemoreceptor cells is relatively unique. It may have effects directly on the vestibular system and on the chemoreceptor trigger zone. It has approximately 280 functional chemoreceptor genes. In front of the ocelli is an additional organ that probably functions as a chemoreceptor. The carotid body is a small cluster of chemoreceptor cells, and supporting sustentacular cells. There are two main classes of chemoreceptor&colon; direct and distance. These medications are thought to stimulate the chemoreceptor trigger zone (CTZ). At very high doses, piribedil has an emetic action on the chemoreceptor trigger zone (CTZ). The chemoreceptor cells taste the water and are sensitive to touch. However, even photoreceptor cells may have evolved more than once from molecularly similar chemoreceptor cells.