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Quick Question

What makes us faint?


So a couple of weeks back, I attended my first DR (dissection room) session with some second year med students. Now, I’m not particularly squeamish so I didn’t really give it a second thought. But here I am, desperately trying not to faint in front of these people. It got me thinking: what is it that makes us faint?

The basic answer is quite simple. Fainting, medically known as syncope, is caused by a restriction of oxygen to the brain and can cause cerebral hypoxia or hypotension. If you are at high altitude (where the air is thinner and the oxygen level lower) or restricted in any way (like with a corset), the body reacts by activating the central ischaemic response. This increases the supply of oxygen to the brain, away from the body. Muscles cannot function without oxygen, leading to falling over. The blacking out is essentially not necessary as you are increasing oxygen to the brain; but by the time the body has started to react, your brain has already perceived the lack of oxygen and reacted.

What I found more interesting was why we faint when there is no physical reason for it. In embarrassing, scary or uneasy situations – like in an operating theatre – it seems quite common to faint. Obviously the heat and extreme light in such rooms does not help the situation. What happens is essentially an anti-adrenaline burst. When in such situations, fainting is called vasovagal syncope as it involves the vagus nerve. Impressively, the vagus nerve is responsible for the innervation of the pharynx (throat), larynx (voice box), trachea (windpipe), lungs, heart, oesophagus, and the intestinal tract as far as the transverse portion of the colon. It also supplies sensory information back to the brain from the ear, tongue, pharynx, and larynx. When caught in a trying position, the vagus nerve gets overstimulated and causes the blood vessels to dilate and the heart to slow down. The lack of blood (and oxygen) causes the black out. So I’ll do my best to control my vagus nerve next time!

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About me

Hi! My name is Natacha - I'm a research scientist and a lover of all things science! I love finding out interesting facts about all aspects of life, whether it's how genetic engineering works or what the difference between crimped and straight hair is. There's a bit of science behind every mystery and the Science Informant will help find the clues for everyone to enjoy and understand the amazing world of science!
Member Button linking to the Association of British Science Writers (ABSW) - an association of science writers, journalists, broadcasters and science-based communications professionals - many of whom are available for freelance work

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