Chemoreceptor trigger zone

The chemoreceptor trigger zone is an area in the medulla oblongata that detects blood-borne and cerebrospinal-fluid substances and can activate neural circuits responsible for vomiting.

Area postrema: A circumventricular structure in the medulla that monitors blood and cerebrospinal fluid for chemical signals. It is the principal anatomical site associated with the chemoreceptor trigger zone.
Dopamine antagonist: A drug that reduces signaling at dopamine receptors. Many antiemetics act at dopamine receptors in or near the trigger zone.
Medulla oblongata: The lower part of the brainstem, connecting the pons with the spinal cord and supporting vital autonomic functions. The trigger zone lies in this brainstem region.
Vestibular system: The sensory system that detects head motion and orientation through structures of the inner ear and their neural pathways. Motion sickness begins with vestibular signals rather than primarily with blood-borne chemicals.
Blood–brain barrier: A selective interface that regulates movement of substances between the bloodstream and central nervous system. The area postrema’s weak barrier protection lets circulating chemicals reach its sensory cells.
Ondansetron: An antiemetic medication that blocks serotonin 5-HT3 receptors. It suppresses vomiting by interrupting serotonin signaling in emetic pathways that include the trigger zone.
Circumventricular organ: A brain structure with specialized blood access that permits monitoring of circulating signals. The area postrema is a circumventricular organ, a structural basis for blood-borne chemical sensing.
Motion sickness: Nausea and related symptoms caused by conflicting or unusual motion signals. It illustrates a route to vomiting that does not depend on chemical detection by the trigger zone.
Vomiting center: A distributed brainstem network that coordinates the motor and autonomic actions of vomiting. The trigger zone can relay chemical alerts to this network to initiate emesis.
Metoclopramide: A medication with dopamine D2-blocking and gastrointestinal prokinetic effects. Its D2 blockade can reduce trigger-zone signaling, while its gut effects address additional nausea pathways.

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