A concussion is defined as a mild traumatic brain injury (mTBI) resulting from a jolt or blow to the head or body that causes the brain to move rapidly within the skull. This sudden movement temporarily disrupts normal brain function, leading to symptoms like confusion, headache, and memory loss. While these symptoms are common, vomiting is an alarming sign, indicating a deeper physiological disturbance. Understanding this connection requires examining the brain’s specialized control center for this protective reflex.
The Brain’s Vomiting Control Center
The mechanism that controls vomiting is housed within the brainstem, the most primitive part of the brain responsible for regulating involuntary functions like breathing and heart rate. Deep within the brainstem’s medulla oblongata lies the core of this system, often referred to as the vomiting center. This center processes incoming signals that might trigger an emetic response.
A specialized area called the Chemoreceptor Trigger Zone (CTZ) plays an important role in this process. The CTZ is uniquely situated outside the protective blood-brain barrier, allowing it to “sample” the chemical composition of the blood and cerebrospinal fluid. Its function is to detect circulating toxins, drugs, or chemical imbalances, acting as an early warning system. If the CTZ detects a problematic substance, it signals the main vomiting center, initiating the muscular contractions that result in vomiting.
Two Primary Ways Concussions Trigger Nausea
A concussion can activate the sensitive CTZ and the vomiting center through two pathways: mechanical pressure and chemical disruption. The physical impact can lead to swelling or bleeding inside the skull, which takes up space within the rigid cranial vault. This increase in volume elevates the intracranial pressure (ICP), causing direct compression of the brainstem where the vomiting center is located.
This physical pressure on the medulla oblongata is a potent stimulus that can override other signals, triggering the vomiting reflex. Vomiting caused by ICP is often forceful and may not be preceded by nausea, reflecting the severity of the pressure on the brain’s regulatory centers. The second mechanism involves a widespread chemical imbalance within the brain caused by the sudden jarring of the injury.
The traumatic forces disrupt the normal firing of neurons, causing an excessive or erratic release of various neurotransmitters, such as dopamine and serotonin. Since the CTZ is exposed to the bloodstream and is rich in receptors, the sudden influx of imbalanced neurotransmitters acts like a toxin. This chemical stimulation directly activates the CTZ, which signals the vomiting center, creating the sensation of nausea and subsequent vomiting.
When Vomiting Requires Immediate Medical Attention
While a single episode of vomiting can occur with a mild concussion due to sudden chemical or pressure changes, persistent or forceful vomiting is considered a serious medical sign. The symptom’s significance shifts from a sign of concussion to a potential indicator of a more severe traumatic brain injury (TBI), such as an intracranial hemorrhage or brain swelling. Medical professionals pay close attention to the pattern and timing of this symptom.
Immediate emergency care is necessary if vomiting is repeated (two or more episodes) or if it is accompanied by other worsening symptoms. These signs include a headache that becomes progressively worse, increasing confusion, slurred speech, or difficulty being roused from sleep. The danger of persistent vomiting is twofold: it can rapidly lead to dehydration, and it suggests that the underlying intracranial pressure is dangerously high and continuing to rise.
A patient experiencing these combined symptoms requires urgent neuroimaging, such as a CT scan, to check for life-threatening structural issues like blood clots or severe swelling. Ignoring repeated vomiting risks allowing a more severe injury to progress, potentially leading to permanent brain damage or death. Even if the initial injury seemed minor, persistent vomiting hours later warrants an immediate visit to the emergency department.