Why do some of us feel dizzy/faint after thinking about or seeing blood?
In: Biology
Vasovogal response or vasovogal syncope.
Vagus nerve is the longest nerve in the body that goes from close to the groin area to your brain area. It is parasympathetic in nature. This means that it works in tandem with the sympathetic system. Parasympathetic system gets triggered when one encounters emotionally disturbing vision, sound or thought, which in short may be called the emotional stress. Since the vagus nerve is a part of the parasympathetic system, it gets stimulated, in fact over stimulated, when faced with emotional stress. When overstimulated, the things and functions it controls go into a tizzy.
So, what really does the vagus nerve control?
It controls sweating, gag reflex, some and many muscles. One such muscle is the heart. When the vagus nerve is stimulated, it slows down the heart. That means the blood is not pumped as well as it needs to. The lower body is not affected by it so much, since the gravity helps in drawing blood to the lower extremities. However, since the brain sits at the top of your body and the flow of blood has to struggle against the gravity even in normal circumstances, when the blood pressure level drops, brain receives far lesser quantity of blood than necessary.
This affects the normal functioning of your ears. You start hearing echoes and voices sound muffled. Your eyes start to lose vision because of the lack of blood. The skin becomes tingly. Speech slurs. And you faint. Since the groin area is also affected by the vagus nerve, people going through emotional stress and overstimulated vagus nerve may pee their pants (happens with children who are being yelled at, for example).
It is an offshoot of the fight, flight, or freeze response. Some people’s nervous system reacts to the sight of blood as if it was a life or death emergency. When that happens, your blood pressure can drop which can reduce blood flow (and therefore oxygen) to your brain. Then you faint.
Latest Answers