YES. Tap a bowl of jell-o. The bowl is your head; the jell-o, your brain. The brain continues after the head stops. And like a wave, back and forth. The delicate vessels between the two weaken or even eventually tear. Each future ''tap'' is added on. Without good blood flow, parts of your brain die. This is origin of ''punch-drunk''.Worse is parkinson-like symptoms-think muhammed ali.
Possibly. There is an entity called chronic traumatic encephalopathy which results from multiple head injuries like concussions or even the multiple hits like a lineman takes. It ususally shows up several years after the injury and presents with mood changes, impulsivity and memory loss, it usually progresses into a dementia. It is associated with tau protein deposition in the brain.
One episode. Of head trauma is not likely to cause dementia unless it is a very serious episode of trauma or multiple episodes of head trauma as in boxers. Rather, one episode of head trauma may cause some memory loss that is not progressive.