The reflex action of vomiting is controlled by the Medulla.

The medulla is a part of the brainstem that controls many vital functions, including reflex actions such as vomiting. Vomiting, also known as emesis, is a complex process involving the coordinated contraction of various muscles to expel the contents of the stomach through the mouth.

Function of the Medulla:
The medulla oblongata is responsible for regulating several autonomic functions, including respiration, heart rate, and blood pressure. It also plays a crucial role in coordinating and controlling various reflex actions in the body, including vomiting.

Medullary Vomiting Center:
The medulla contains a specific region called the medullary vomiting center, which is responsible for coordinating the vomiting reflex. This center receives input from several sensory receptors located throughout the body, including the gastrointestinal tract, inner ear, and chemoreceptor trigger zone in the brain.

Triggering the Vomiting Reflex:
When the body detects something harmful or toxic, such as spoiled food or a noxious odor, sensory signals are sent to the medullary vomiting center. These signals are processed, and a series of coordinated responses are initiated to expel the contents of the stomach.

Coordination of Muscles:
The medulla sends signals to various muscles involved in the vomiting reflex, including the diaphragm, abdominal muscles, and muscles of the throat. The diaphragm contracts forcefully, causing a sudden increase in intra-abdominal pressure. At the same time, the muscles of the abdomen contract, and the lower esophageal sphincter relaxes, allowing the contents of the stomach to move upward. The muscles of the throat also contract, closing off the airway and preventing the entry of vomit into the lungs.

Conclusion:
In conclusion, the reflex action of vomiting is controlled by the medulla. This region of the brainstem coordinates the various muscles involved in the vomiting reflex to expel the contents of the stomach. The medullary vomiting center receives input from sensory receptors located throughout the body and triggers the appropriate responses to protect the body from harmful substances.