Can someone please dumb this down for me in layman terms

[connieblue]

I'm taking the intro psychology clep and want to make sure i have the biological questions grasped before I take it.

I provided a link and even though the link is made specifically for dummies on the subject, I'm still having a hard time understanding it.

LINK -https://www.dummies.com/education/scienc...-impulses/

If anyone could explain the link in simpler terms in the response to this thread, I would be extremely grateful.

Thanks Connie.