Actually, all they really are is a little cluster of neurons.

It involved sending signals of extreme pain from every nerve cell in his body

They're divided into 2 groups:

is caused by deterioration of the cerebellum,

In the human brain there are about 140 billion neurons and

10 times more cells, which give orders to those neurons.

It's a neurodegenerative disease of unknown origins. Nerve cells begin to break down, eventually completely disappearing.