Then there are those few unlucky people with glass jaws . . . .
If you follow your jaw back to where it joins the skull, the mandibular joint, you will see that it joins the head near the base of the ears (well, kinda near). If you place your fingers below the joint, you should be able to feel your pulse quite strongly.
Your fingers are directly over the carotid arteries. The carotids are the main arteries into the head, though you also have vertebral arteries going up your spine. But the carotids are the ones that are really interesting.
One carotid goes up each side, and branches near where your fingers are located into the inferior and superior carotid. At the junction, there is a physiologically important area that contains a large quantity of nerve endings.
These nerve endings sense some critical information about the blood before it goes gushing into your skull. It senses the oxygen content, possibly carbon dioxide content, and definitely blood pressure.
The receptors that check blood pressure at this branching point are called the carotid baroreceptors, and they are responsible for making sure you get plenty of the vino vitae into your brain. If blood pressure drops, they signal for an increase in heart rate and contractility, if the blood pressure rises, they signal the heart to slow down.
It just so happens that they really don’t measure just blood pressure, but pressure on the notch. If you jab your finger right on top of this sensor, you can fool the sensor into thinking that it is your blood pressure that went through the roof, not that you’re just pushing on the sensor itself. Then the body compensates by dropping blood pressure, which happens fairly rapidly.
Heart output drops, and you pass out from the pressure reduction in the brain.
Go ahead. Try it. Push real hard.
It is believed that a glass jawed person has a loose mandibular joint that allows a good solid thwack to cause a pressure wave that sets off the baroreceptor, lowering blood pressure, and down they go.
Grabbing the baroreceptor is also a common trick that the military and police use to subdue the proles. Punch a thumb into that area, and you’ll put them to sleep right fast.
But . . .
There is a critical nerve that runs right next to this branching point of the carotid. This nerve, called the vagus nerve, is important for controlling heart rate and damn near everything else that happens below your neck. If this nerve is damaged, the immediate damage can cause the nerve to stop the heart, and if the nerve is permanantly damamged, you’ll never shit right again, if ever.
Just thought you ought to know that before the teeming millions start thumb punching each other in the neck.