This quick motion of causes trauma to the brain that knocks the recipient out leaving him unconscious. Points on the jaw that are especially vulnerable to knockouts are the sides of the chin, and where the jaw is attaches to the skull. When the jaw is punched, the head quickly accelerates around.
After a fraction of a second, it quickly decelerates as muscles, tendons, and bones prevent the head from spinning any further. The brain inside the skull is floating in fluid 2. It accelerates slower than the rest of the head. This forces it to crash into the inside of the skull when the head stops. When the brain slams into the inside of the skull, it suffers trauma. It then bounces off the inside of the skull and slams into the opposite side.
This causes even more trauma. Several markers have been used, including horseradish peroxidase HRP with a radius of 3 nm 28 , 30 , 3, Da dextran-tetramethylrhodamine TRITC-dextran with a radius of approximately 1 nm 31 , 32 , and Lucifer Yellow with a radius of 0. At least a subset of the pores would thus have to have a radius of at least 3 nm, although some may be larger, and if the pore size distribution is wide, the majority of pores may be smaller.
While influx of molecular marker can be used to estimate the size of the pores, it does, however, not provide any information about the shape of the pores or the orientation of the phospholipids at the edge of the pores. Since it relies on the diffusion of labeled molecules, it can also only give a rough estimate of the kinetics of pore formation and resealing.
Recent computer modeling has, however, demonstrate that pores can form in a fraction of a second following cell membrane stretching, although the kinetics of pore closure has not been evaluated 34 , Computer modeling also indicates that pore formation within the cerebral cortex inhibits action potential generation 36 , consistent with the loss of consciousness without seizures that is typically observed in boxing knockouts. Whether the seizure-like activity that sometimes is observed following knockout can be explained by mechanoporation is, on the other hand, still an open question.
However, passageways through the cell membrane are normally stabilized by proteins, such as aquaporins or ion channels, to avoid exposing the hydrophobic phospholipid tails to water molecules. This makes it important to consider how pores without a protein component are stabilized and for how long they can remain open. While existing mechanoporation studies do not address these issues, there is an independent line of research that does, namely electroporation 36 , In the experimental electroporation method, an electrical current is passed through a cell suspension, which induces cell membrane pores that stay open long enough to allow genetic material to diffuse into the cells.
According to current theories in this field, the pores can either be hydrophobic or hydrophilic 38 , depending on the orientation of the phospholipids within the membrane Figure 2. Based on what is known from kinetic studies, hydrophobic pores are inherently unstable and closes in a fraction of a second while hydrophilic pores does so in a timeframe of seconds to minutes 39 , Possible arrangement of phospholipids in a pore created by mechanoporation.
A Preinjury cell membrane, where the circles indicate the hydrophilic phospholipid head groups and the lines indicate the hydrophobic phospholipid tails. B Phospholipid configuration in a hydrophobic membrane pore, where the hydrophobic tails face the edge of the pore. This type of pore is thought to be highly unstable and close in a fraction of a second.
C Phospholipid configuration in a hydrophilic pore. Here, the polar head groups face the edge of the pore which prevents the pore from immediately collapsing. The crowding of the fatty acid tails at the edges does, however, causes instability and will, within minutes, lead to the closure of the pore.
It can be argued that once a pore has been formed, the kinetics of resealing should be independent of the nature of the forces that lead to its creation. If this is true then porated neurons in a knocked-out boxer would be resealed within minutes, leading to the return of consciousness.
Thus, the timeframe for both the formation and the spontaneous closure of the pores are a good match for the observed symptoms. The experimental evidence for mechanoporation is, however, so far indirect and relies on influx of marker substances in animal models and in silico modeling.
More direct evidence, such as visualization of actual pores, is still not available and more work remains before mechanoporation can be considered fully verified.
It may be that seeing a person being knocked out, and then rapidly regaining consciousness, is so common that it is taken for granted. But from the above description, it should be clear that this sequence of events is difficult to explain on a cellular and molecular level.
Compared with concussion in general, the patient characteristic and mechanical forces in the boxing knockout are very homogeneous and may therefore serve as a suitable starting point. Admittedly, the timescale of the primary injury precludes any medical intervention and future therapeutics would therefore have to target secondary injury processes. A fully verified and detailed description of the primary injury in boxing knockouts, and concussion in general, would be very useful though.
It could potentially make it possible to define a safe level of mechanical strain on brain tissue, which would aid in the design of protective equipment and the regulation of sports.
An increased understanding of the pathophysiological mechanism would also increase the chances of finding better treatments for patients with postconcussive syndrome, chronic traumatic encephalopathy, and diffuse axonal injury. And perhaps a better understanding of how consciousness is lost may be a first step toward understanding consciousness itself. AH drafted the original manuscript. ER contributed novel ideas, insights, and knowledge to the final manuscript. Both authors contributed to the article and approved the submitted version.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Thanks to professor Per Enblad for valuable comments on this manuscript and to Tim Howells for careful proofreading. National Center for Biotechnology Information , U. Journal List Front Neurol v. Front Neurol. Published online Oct Author information Article notes Copyright and License information Disclaimer.
Reviewed by: David F. Giglio, Italy. This article was submitted to Neurotrauma, a section of the journal Frontiers in Neurology. Received Jun 8; Accepted Sep The use, distribution or reproduction in other forums is permitted, provided the original author s and the copyright owner s are credited and that the original publication in this journal is cited, in accordance with accepted academic practice.
No use, distribution or reproduction is permitted which does not comply with these terms. Abstract Several hypotheses have been put forth over time to explain how consciousness can be so rapidly lost, and then spontaneously regained, following mechanical head trauma.
Keywords: traumatic brain injury, concussion, boxing, mechanoporation, mechanosensitive MS ion channel. A History of Knockouts The proportions of the human hand differ from other primates, which tend to have longer fingers. Symptoms of a Punch A strike to the head which does not lead to unconsciousness may still induce a state characterized by reduced reaction speed and confusion.
The Biomechanics of a Knockout For a punch to damage the brain, the force from the impact must somehow be transferred through the skull and into the brain tissue. Open in a separate window. Figure 1. The Convulsive Hypothesis According to this hypothesis, the mechanical forces of the impact trigger a depolarization of the neuronal cell membrane, which leads to uncontrolled release of action potentials.
Vascular Hypotheses When a knockout is fatal, a CT scan typically reveals extensive cerebral hemorrhage, which makes it reasonable to assume that tearing of blood vessels is the main form of primary injury in this case. Microtubule Breakage Normal body movements lead to stretching of axons in the peripheral nervous system which can readily adjust their length without damage in this case Mechanosensitive Ion Channels Mechanosensitive ion channels are found in several parts of the body, for example, the heart, urine bladder, and inner ear, where they are required for normal physiology.
The Mechanoporation Hypothesis Pore formation in a cell membrane induced by mechanical forces is referred to as mechanoporation, which primarily has been investigated by using molecular markers to evaluate cell membrane permeability following experimental brain trauma 28 , Figure 2. Benefits of Understanding Knockouts It may be that seeing a person being knocked out, and then rapidly regaining consciousness, is so common that it is taken for granted.
Author Contributions AH drafted the original manuscript. Conflict of Interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Acknowledgments Thanks to professor Per Enblad for valuable comments on this manuscript and to Tim Howells for careful proofreading. Footnotes Funding. References 1. Protective buttressing of the human fist and the evolution of hominin hands. J Exp Biol. Concussion: the history of clinical and pathophysiological concepts and misconceptions.
Concussion is confusing us all. Pract Neurol. Martland HS. Punch drunk. Experimental concussion. Proc R Soc Med. Cournoyer J, Hoshizaki TB. Head dynamic response and brain tissue deformation for boxing punches with and without loss of consciousness. Clin Biomech. The same blow to the chin or side of the jaw area is a different matter. Tibi is a science journalist and co-founder of ZME Science. He writes mainly about emerging tech, physics, climate, and space.
In his spare time, Tibi likes to make weird music on his computer and groom felines. February 22, Reading Time: 4 mins read.
Credit: Pixabay J ab, jab, right hook. Get more science news like this Tags: Blacking out brain Punches Unconscious. Share Tweet Share.
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