A smile muscle is the risorius muscle which serves as the muscle of facial expression.
The risorius muscle's function is to aid in facial expression by pulling the corner of the mouth laterally via its contraction in an outward and upward motion.
In conjunction with other facial muscles, this helps to create a smile or a frown, and myriad other expressions in-between.
In a smile, the absence of movement in the outer part of the muscle that orbits the eye (orbicularis oculi pars lateralis, in Latin or AU 6 in FACS terms) distinguishes a fabricated smile from the genuine thing.
The muscle that is called the kissing muscle is the orbicularis oris muscle which is a muscle that surrounds the mouth and forms the lips.
The orbicularis oris muscle is often called the kissing muscle as it is what enables you to pucker.
Orbicularis oris muscle, also known as musculus orbicularis oris is a complex, multi-layered muscle which attaches through a thin, superficial musculoaponeurotic system to the dermis of the upper lip and lower lip and serves as an attachment site for many other facial muscles around the oral region.
In common language, the orbicularis oris is often referred to as 'the kissing muscle.
It allows for facial expression, and more specifically, it is responsible for puckering the lips.
While this action is a requirement for kissing, the puckering action is used in a number of other ways.
A sphincter muscle closes circumferentially.
Therefore, the orbicularis oculi muscle plays a vital role in facial expression and various ocular reflexes such as frowning, squinting, and eye closure.
There is a palpebral portion that can be contracted actively and passively.
Kissing can involve a variety of different facial muscles, with the orbicularis oris being the main skeletal muscle involved.
Simple kisses use as few as 2 muscles and burn only 2 to 3 calories, whereas passionate kissing can involve as many as 23 to 34 facial muscles and 112 postural muscles.
The orbicularis oris muscle is supplied by the buccal and mandibular branches of the facial nerve.