The primary part of the brain implicated in triggering vomiting, particularly in response to certain substances in the blood, is the area postrema (AP).
Understanding the Area Postrema
For over 40 years, the area postrema has been recognized as a crucial region for initiating vomiting. It serves as a key part of the brain's complex system for detecting potentially harmful substances.
Location of the Area Postrema
Based on research, the area postrema is precisely located:
- On the dorsal surface of the medulla oblongata: This is a part of the brainstem, which connects the brain to the spinal cord.
- At the caudal end of the fourth ventricle: This is a cavity within the brain that is filled with cerebrospinal fluid.
Think of its location like this:
| Brain Region | Specific Location | Role in Vomiting |
|---|---|---|
| Medulla Oblongata | Dorsal surface, caudal end | Contains the Area Postrema and other reflex centers. |
| Fourth Ventricle | Bordering the Area Postrema | Adjacent brain structure. |
| Area Postrema | Within the medulla, near ventricle | Chemoreceptor trigger zone for vomiting. |
Role as a Chemoreceptor Trigger Zone
The area postrema is often called a "chemoreceptor trigger zone." This means it contains specialized receptors that can detect chemicals in the bloodstream. Unlike most of the brain, the area postrema is located outside the blood-brain barrier, allowing it direct access to circulating blood.
This unique position enables it to sense various substances that might induce vomiting, such as:
- Certain toxins or drugs
- Chemotherapy agents
- Some hormones
When the area postrema detects these substances above a certain threshold, it sends signals to other parts of the brainstem that control the physical act of vomiting, initiating the emetic reflex.
While the area postrema is the primary trigger zone for chemical stimuli, the vomiting reflex is complex and involves coordination from several brain regions, including the vomiting center itself (also in the medulla oblongata) and pathways from the gastrointestinal tract and other sensory systems. However, the area postrema is indispensable for triggering vomiting in response to blood-borne emetics.
