Consciousness is an electrical and chemical interaction in the brain, caused by neurons firing and chemical interactions. How does a mechanical "force" cause this to stop working?

i.e. How does a mechanical action (such as a punch to the head) cause this electrical/chemical system to stop working (leading to unconsciousness)?

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    $\begingroup$ One basic point I can offer is that any proteinaceous structure is force-sensitive. Neurons are soft matter and they're intrinsically sensitive to mechanical forces, right down to the chemical level. So if you picture what an ion channel is, a gate that can be opened or shut through thermal energy, it's easy to see how a density fluctuation (like a sound wave) could flip it between states. $\endgroup$
    – Ryan
    Commented Sep 12, 2013 at 23:27

3 Answers 3


Mechanical force can compress neurons and cause action potentials as you probably experienced in the form of hitting the funny bone. Strong enough acceleration of the brain tissue may be causing massive excitation of neurons as indicated by animal EEG study. It suggests that the loss of consciousness is due to generalized epileptic seizure. However, it is not fully agreed upon: quoting wikipedia entry on Concussion:

It is not known whether the brain in concussion is structurally damaged or whether there is mainly a loss of function with only physiological changes.[14][needs update] Cellular damage has reportedly been found in concussed brains, but it may have been due to artifacts from the studies.[15] It is now thought that structural and neuropsychiatric factors may both be responsible for the effects of concussion.[16]

And following quote is from this

The brief loss of consciousness that characterizes concussion appears to be the result of rotational forces exerted at the junction of the upper midbrain and thalamus that cause transient disruption of the functioning of the reticular neurons that maintain alertness. (Allan H. Ropper, M.D., and Kenneth C. Gorson, M.D.; N Engl J Med 2007; 356:166-172 January 11, 2007)

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    $\begingroup$ so are you saying that the process is not actually well understood? There seems to be alot of unknown about the process? $\endgroup$
    – Laurence
    Commented Sep 14, 2013 at 13:14
  • $\begingroup$ @TheShiftExchange Unfortunately, that seems to be the case. $\endgroup$
    – Memming
    Commented Sep 14, 2013 at 13:34

Loss of consciousness, or syncope, can be caused by a number of factors, almost all of which relate to lack of proper blood flow: high G-forces, low blood pressure, low blood sugar, cardiac arrhythmia, and vasovagal responses, such as when I give blood. These all make sense and are moderately well understood. The mechanism of loss of consciousness due to mechanical trauma, however, is less well understood, in part because it can be tricky to study. It almost definitely has to do with lowered blood flow as well, and in particular direct trauma to the brain stem, which regulates consciousness.

Basically, you need to rattle the brain inside its cage, slamming it against the skull. The easiest way to get knocked out from a punch is usually to the chin; the rotational force is much harder for the brain to cushion against, and is a very sharp force. The displacement of the brain from such a force can compress blood vessels, cutting off blood flow to the brain. There's also some evidence that the higher brain and the brain stem can twist around each other, which certainly worsens things. There's even a theory that consciousness is rooted in the neurological structure, which might support the idea that unconsciousness is caused by parts of the brain inhibiting each other.

ETA This isn't exactly a reliable source, but the guy writing this piece for Deadspin is board-certified in internal medicine, and had this (uncited) to say:

Researchers have examined the brain waves of recently concussed animals and determined that their brains resemble that of an animal suffering an epileptic seizure. This comes as a bit of a surprise, because the brain waves (measured by an electroencephalogram) show hyperactivity, which implies that when a fighter is glassy-eyed and unable to answer the referee's questions appropriately, his neurons might actually be overactive, not underactive.

But a hyperactive brain is not the only problem. When the head is hit at high speed, shearing movements within the skull can cause micro-hemorrhages of the blood vessels within the brain tissue. If the shearing force is large enough, or if the head is it hard enough, a large bleed can occur. This becomes a medical emergency because the skull is fixed, enclosed space. As blood accumulates, usually in the form of a subdural hematoma, it can squish the brain and potentially compromise critical neural functions like breathing; death becomes imminent.


A hit can break blood vessels, produce inflammation and exert pressure in the brain tissue. Pressure in fact can alter the composition and distribution of the cerebrospinal fluid. Since the nervous cells are very sensible to oxygen deficit and the composition of their surroundings, phisical damage can lead to loss of brain function. Moreover, while it's true that cerebral activity is due to chemical reactions, it's also true that this activity must be focused in very specific points (synapses), wich may be damaged by an strong hit.


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