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For a time, when I was younger, I believed I had the power to inflict terrible injury using just my finger and thumb. The Vulcan nerve pinch on Star Trek had become conflated in my mind with the karate chop used to such apparently fatal effect in other TV shows. It was clear to me that – of all the regions of the body – the side of the neck was particularly vulnerable. I worried that I was going to kill someone by accident. How would I handle this mighty power?

There are lots of vital structures in the neck, including the major vessels supplying the brain: the carotid arteries. The great hosepipe of the ascending aorta leaves the heart and rises for a few centimetres before arching over and travelling down the length of the spine. The right and left common carotids arise from the arched section, making them full of freshly oxygenated blood. From the chest they continue up into the neck: if you roll your fingers into the trough at the side of your windpipe, you can feel your carotid pulsing.

Just above the Adam’s apple the common carotids branch to become the internal and external carotids. The external carotid remains nearer the surface to supply the tissues of the face and neck. There is an ancient surgical tradition of making students recite all of its branches, a nightmare never better described than in Samuel Shem’s 1978 novel House of God. “Running through my mind, over and over like Muzak, was a mnemonic for the branches of the external carotid artery: As She Lay Extended Olaf’s Potato Slipped In. And even there, the only one I could remember was Olaf’s, which stood for Occipital. And what the hell use was that?”

The internal carotid dives deeper and eventually supplies the brain. It is one of the most vulnerable structures in the neck, but the threat is from atherosclerosis rather than Dr Spock. Any artery can become “furred up” or stenosed by atherosclerotic disease: as fat-filled plaques are deposited on its walls, the blood vessel narrows. In severe stenosis, the internal carotid, which is ordinarily as roomy as a McDonald’s milkshake straw, becomes more than 70 per cent occluded. This tiny tube, more like the little straw attached to a carton of apple juice, still has to carry the blood supply for a substantial part of your brain. Atherosclerotic plaques can also erode or rupture: when this happens, the body tries to patch the damaged areas with clotted blood, which only makes the artery narrower still (and leads to potential disaster if the clots break off and are carried up into the brain).

You can sometimes hear the disruption that carotid stenosis causes to the flow of blood, which is why a doctor might place a stethoscope on the side of your neck (“There’s no lungs up there, love!” a patient advised me). If there is significant stenosis, the blood squeezing through the channel churns and bounces off the walls, causing a rumbling sound called a bruit, which gets louder as the vessel becomes more and more occluded (before tapering off altogether if the obstruction exceeds 90 per cent).

A severe carotid stenosis may eventually deprive part of the brain of its blood supply. If the blood flow is then restored, you will only suffer a transient ischaemic attack, or “mini-stroke”, a temporary derangement of your neurology. But a TIA should never be ignored, as it suggests something may be seriously amiss with your carotid arteries. If the interruption to the blood flow is more prolonged, the brain tissue will die, causing a stroke. No karate chop was ever as devastating.

Sophie Harrison is a hospital doctor in South Yorkshire

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