what is the definition on smile and how they work?

Answer 1

Just like your avatar. Just open your mouth wide.

Answer 2

I've been hearing this for years. Supposedly it takes fewer muscles to smile than to frown; ergo, you should smile. Happiness, it seems, is the lazy person's emotion. Time to put this platitude to rest. I arrived at the following detailed accounting of the relevant muscles with the aid of David H. Song, MD, FACS, plastic surgeon and assistant professor at the University of Chicago Hospitals. Song, among other things, reconstructs faces--in short, he ought to know. My apologies if this list seems obsessive, but we're going to settle this once and for all. Caveat: Deciding which of the 53 facial muscles are important in smiling or frowning is a bit arbitrary--many make only minor contributions, and depending on the intensity of the expression may not be involved at all. I've listed here the ones Song feels are important, as corroborated by other sources.

Muscles involved in a "zygomatic" (i.e., genuine) smile:

Zygomaticus major and minor. These muscles pull up the corners of the mouth. They're bilateral (one set on either side of the face). Total number of muscles: 4.

Orbicularis oculi. One of these muscles encircles each eye and causes crinkling. Total: 2.

Levator labii superioris. Pulls up corner of lip and nose. Bilateral. Total: 2.

Levator anguli oris. Also helps elevate angle of mouth. Bilateral. Total: 2.

Risorius. Pulls corner of mouth to the side. Bilateral. Total: 2. Grand total for smiling: 12.

Principal muscles involved in a frown:

Orbicularis oculi (again). Total: 2.

Platysma. Pulls down lips and wrinkles skin of lower face. Bilateral (though joined at midline). Total: 2.

Corrugator supercilii (bilateral) and procerus (unilateral). Furrow brow. Total: 3.

Orbicularis oris. Encircles mouth; purses lips. Unilateral. Total: 1.

Mentalis. Depresses lower lip. Unilateral. Total: 1.

Depressor anguli oris. Pulls corner of mouth down. Bilateral. Total: 2. Grand total for frowning: 11.

Despite the fact that smiling uses more muscles, Song believes it takes less effort than frowning--people tend to smile more frequently, so the relevant muscles are in better shape. You may feel this conclusion assumes a rosier view of the human condition than the facts warrant, but I defer to the doctor. Incidentally, a superficial, homecoming-queen smile requires little more than the two risorius muscles. So if your goal in expressing emotion is really to minimize effort, go for insincere.

The use of several muscles that form a facial expression that people consider happy. and there is how it works have a good one.

Answer 3

If you ask definition.
smile (sml)
n.
1. A facial expression characterized by an upward curving of the corners of the mouth and indicating pleasure, amusement, or derision.
2. A pleasant or favorable disposition or aspect

If you ask how they work?
It's because your face muscle.

if you ask "how could a single smile could make someone's life brighter?"
That's what world should say "MAGIC".
Or Psychologists would say, that's the effect of psychology