1. Everybody is different and thus affected differently.
2. The brain floats and when it hits the skull like in some whiplashing clinch techniques it causes what is known as "flash" or "flash over" when u see a flash and are dazed. Usually happens when you get rocked but not KO'd.
3. TMJ (temporomandibular joint)... The movement of the lower jaw or "Mandible" back and upward causing the KO also known as getting hit on the "button" - see also: Dan Henderson vs Mike Bisping for reference.
Neck strength could help to keep from getting flashed in the clinch but it wont help the TMJ