A long while back, one of the finest teachers I have ever encountered described life as "an inexorable march to the junk heap."

He was referring specifically to the physical and economic tenure of material things, noting that their lives couldn't be extended forever, but could be lengthened by attention to proper maintenance.

At the same time, and with a knowing wink, he applied that principle to human existence.

While his observation was then worth little more than a classroom cackle, I now see, from the vantage point of my present vintage, an abundance of evidence that the comparison was valid, profound and prophetic.

While we are all destined to kick the bucket with undeniable certainty, many of the zigs and zags between cradle and grave are manageable with proper attention, planning and discipline.

The six-pack abs of my Marine Corps youth now exist solely in fading photographs, but the one-sack sag which has replaced them might have been avoided in large part by not defecting to the Corps of Couch Potatoes later in life.

The inflexible rule of muscledom is "use 'em or lose 'em," and our national adoption of the latter option is evidenced by the decline of so much of America to a nation of human dough balls.

Happily, it is also the potential of muscles to rise from a zombie-like state to their former firmness through exercise and dietary sagacity.

Our focus here is on the most powerful of our muscles, although it is seldom thought of in that category.

The human brain will not move itself a single inch in a lifetime and cannot, unaided, lift a fallen hair. Yet it is the principal source of our strengths and weaknesses, as well as the control center of our very existence.

Consider these facts: That rather unattractive blob encased between our ears comprises less than two percent of our body weight, but contains a hundred billion very active neurons in the silent universe of our subconscious, intercommunicating at a reported rate of more than 4,000 messages per second, or an incredible 15 million "conversations" every hour - 24/7. (Like, WOW?)

While we busy ourselves with the relatively simple business of conscious activities, it automatically controls such critical matters as our heartbeat, breathing and other bodily functions, simultaneously monitoring the myriad memories, perceptions, prejudices, opinions, reactions, attitudes, wishes, goals, fears and other "stuff" stored there during previous experiences.

If you doubt its importance, just time yourself while putting on a jacket; then do the same, leading with your opposite arm - or just change hands while manipulating a mouse.

The brain is, in a very real sense, a mighty muscle, subject to atrophy if not used, but capable of restoration regardless of advanced age and/or protracted neglect.

There is no longer any doubt about the physical benefits of exercise at any life stage. Senior sedentarians who walk briskly a mere 20 minutes each day cut their risk of stroke by an astonishing 57 percent, among a bunch of other benefits, including the conversion of baggy blubber to solid muscle mass.

Perhaps even more significant is that exercise sends oxygen-rich blood rushing to those ancient brains, recharging and rejuvenating millions of sleepy cells. Also sent thither are endorphins, which effectively combat the emotional blahs that accompany one's approach to the Gulag of Geezerland.

In addition to the stimulation provided by physical activity, you can jazz up your gray matter with mental gymnastics as simple and readily available as engaging in board and card games, doing crossword puzzles, participating in new activities, pursuing hobbies, socializing in unfamiliar spheres, reading books (both fiction and non-fiction) and expanding your vocabulary.

A deadly enemy of self-betterment is the inactive lifestyle now so pervasive in America at all ages, characterized by our addiction to the boob tube and other passive pursuits.

Just as physical activity slows one's "inexorable march to the junk heap," mental exercise mitigates the impact of oldtimers' diseases, including such major inconveniences as failing memory and crushing boredom.

Neither form of activity is likely to result in your candidacy for a centerfold or transform your emotional backyard into a Garden of Eden, but if there really is a chicken soup for the soul, these are two essential ingredients.

As to the brain exercise prescription, there's no need to ask your doctor if it's right for you!

If the truth be known, it probably wouldn't do him or her any harm, either!