How Physical Exercise effects the brian?

I read in the texts that exercise have an impact on age-related memory performance.I say that if a person exercise or not this effects when assessing memory abilities in later adulthood. It is also said that people who exercise maintain mental health scores . I am so interested in this topic because I want to know all that I can about how to keep my memory , Because I worked with patients with memory lost and that is not a good situation to be in.