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)?
Answer
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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