When Simmons shows Coulson the "brain cells", they clearly lack axons/dendrites, which are branchings from the cell walls that make neurons easily identifiable. Brain cells normally use these branches to produce tiny electrical impulses. The cells shown look like red blood cells.
After examining a fried brain, Simmons says it's been hit by 2,000 mega Joules of electricity, and notes that is almost double the power of a lightning bolt. Albeit there is no real minimum or maximum power for a lightning bolt. All lightning bolts vary wildly in power so the concept of double the power of a lightning bolt makes no sense.