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The pathophysiology behind the "knockout punch", though generally thought to be a simple concept of shutting down the brain because of a suddent impact of energy, is in reality, a complicated one. Knowledge of the anatomy and physiology of the brain, though helpful in understanding this, is way beyond the scope and ambition of this article. But one quote, from a neurologist experienced with post traumatic brain injuries, puts the overall concept of the brain into perspective. FYI, axons are the nerve cells that, by numbers of millions and millions, all interact and interconnect to form the almost gelatinous mass of the brain. The brainstem is the area between the brain, which lies in the skull, and the spinal cord, which transmits the information down to the rest of the body.

The first time I was up close to a "living brain" was about 20 years ago during surgery in a young man with intractable epilepsy. I was amazed when I touched its surface with my finger-so soft! I don't know why I was surprised, but somehow I expected something so important to be more substantial than what looked and felt like a big chunk of pulsating, grey Jello.

I think that memory of the brain's velvet vulnerability motivated me to write about boxing and other contact sports. When observing a roundhouse blow, I imagine that precious glob of tissue shuddering in its pool of cerebrospinal fluid, veins and arteries stretched to the point of tearing, axons shearing, and just a bit of a twist on the brainstem, maybe enough for a knockout. While boxing may have other merits, protecting the brain isn't one of them. (The high speed collision of two NFL helmets also makes me wince.)  Andrew Wilmer MD

There appear to be at least 3 different mechanisms for a knockout:

1. Stimulation of the trigeminal nerve, vagus nerve, or carotid sinus causes a reflex drop in heart rate, cerebral blood vessel constriction, and peripheral blood vessel dilatation, a "neurovascular knockout." This knockout occurs because of a neural reflex drop in cerebral perfusion, either because of localized blood vessel constriction, or a drop in cardiac output because of a slower heart rate (bradycardia) or a drop in blood flow return to the heart because of dilation of neurally induced dilation of blood vessels throughout the body.

2. Strikes to the side of the head or the angle of the jaw from a punch known as a "hook" result in rotational forces that can disrupt brain function by one of four hypothetical mechanisms: a) twisting of the brainstem with disturbance of the reticular activating system, b) stimulation of the trigeminal nerve, c) activation of the carotid sinus, and d) diffuse axonal injury. The reticular activating system is a small area in the brainstem which controls "wakefulness" and the sleep wake cycle.

3. The "pummeling knockout," which occurs without loss of consciousness, but with dissociation and confusion. This type of knockout is believed to be caused by traumatic disruption of neuronal activity. Traumatic disruption includes shearing of axonal connections, localized edema which inhibits neural functioning, and disruption of neural cell membrane function which effectively shuts down function of brain nerve cells.

Of course knockouts may present concomittantly with cerebral contusions, subdural hematomas, epidural hematomas, intracerebral hematomas and concussions. These are discussed elsewhere. Let us continue with an evaluation of a analysis of the damage suffered by amateur boxers who are subject to non-knockout blows to the head.