Which muscle contracts during smiling?

The zygomaticus muscle is the key muscle involved in the action of smiling. This muscle is primarily responsible for elevating the corners of the mouth, allowing for the expression of joy or happiness. When it contracts, it pulls the corners of the lips upward and outward, facilitating a smile.

Understanding the role of the zygomaticus muscle places it in direct context with facial expressions and emotional signaling, which are crucial components of non-verbal communication. In contrast, the other muscles listed do not contribute to the action of smiling; for example, the masseter is primarily associated with chewing and jaw movement, the deltoid plays a critical role in shoulder movement, and the sartorius is mainly involved in hip and knee flexion.