A smiling muscle is the risorius muscle, a muscle of facial expression that contributes to smiling.
While it's often referred to as the smiling muscle, it's important to note that the zygomaticus major is actually the primary muscle responsible for drawing the corners of your mouth upwards when you smile. The risorius assists in creating a broader, sometimes more forced-looking smile.
Risorius Muscle Details:
- Function: The risorius muscle retracts the corner of the mouth laterally (sideways), contributing to the widening of the smile. It's more active in wider or forced smiles.
- Variability: The risorius muscle is not present in everyone. Its presence and size can vary significantly among individuals.
- Location: It originates from the fascia over the masseter muscle (cheek) and inserts into the skin at the corner of the mouth.
- Nerve Supply: It is innervated by the buccal branch of the facial nerve (cranial nerve VII).
Other Muscles Involved in Smiling:
Besides the risorius, other muscles contribute to smiling, including:
- Zygomaticus Major: The main smiling muscle, responsible for pulling the corners of the mouth up and outwards.
- Zygomaticus Minor: Helps elevate the upper lip.
- Orbicularis Oculi: Contracts around the eyes, producing "crow's feet" and contributing to a genuine or Duchenne smile.
- Levator Labii Superioris: Elevates the upper lip and can contribute to a slight sneer, depending on the context.
In summary, while the risorius is called the smiling muscle, it works in conjunction with several other muscles to create a range of smiles. Its contribution can vary from person to person, and it may not even be present in everyone.
